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Over what distance are plant volatiles bioactive? Estimating the spatial dimensions of attraction in an arthropod assemblage
Abstract
As studies demonstrating attraction of natural enemies to synthetic herbivore‐induced plant volatiles (HIPVs) accumulate, it is becoming increasingly important to investigate how deployment of these compounds influences arthropod behavior and distribution in the field. There is currently an unexplained dichotomy in the literature regarding the distance over which HIPVs are thought to be effective. It is assumed that these compounds increase recruitment of natural enemies into fields, whereas experiments have found the effects of attraction to dissipate as little as 1.5 m from lures. Through the use of the common HIPV phenylethyl alcohol in soybean [Glycine max (L.) Merr (Fabaceae)] fields, we used replicated mini plots to test the spatial scale and consequences of attraction by analyzing the response of a complex arthropod community to HIPVs along a distance gradient from the HIPV source. Although repellent effects were more common than attractive ones, we found that insect responses to HIPVs are generally consistent out to a range of 8 m, corroborating the idea that volatiles can influence a wide area and are capable of increasing arthropod recruitment at a field scale. Evidence of redistribution (i.e., depletion of patches surrounding HIPV‐augmented plots) was found for a single taxon, braconid wasps, for which augmentation occurred around the lure, but with a reciprocal decline in abundance at greater distances from the emission site. These results are both encouraging and cautionary. Although broad‐scale diffusion of HIPVs appears to be common, redistribution of key predators and/or parasitoids may complicate natural enemy management on a landscape scale by aggravating pest outbreaks in areas robbed of their normal carnivore assemblage.
... source is disturbed by air turbulence, the odour plume will consist of different filaments that follow the direction of the wind (Sabelis & Schippers, 1984;Geier et al., 1999), and it will become mixed with more and other volatiles from the environment (Myrick et al., 2009;Aartsma et al., 2017). Nonetheless, if the air turbulence and wind speed are high, the qualitative composition of the odour blend and ratios of various volatile compounds may remain conserved (Vickers, 2000), which may induce insect responses over longer distances (Glinwood et al., 1998;Langhof et al., 2005;Braasch & Kaplan, 2012). Whether or not air turbulence may have played a significant role in our study remains unknown, although air turbulence is expected to be low in greenhouse environments if ventilators are not operational or windows are closed, as was the case in our study. ...
... These results align with a previous study showing that aphid parasitoids like Aphidius and Praon could be attracted by the aphid pheromone nepetalactone over a distance of at least 1 and 3 m, respectively (Glinwood et al., 1998). Likewise, insects, such as those belonging to the family Psilidae, could be attracted to the common HIPV phenylethyl alcohol over a distance of 8 m (Braasch & Kaplan, 2012). Similar results have been reported for methyl salicylate-based lures, which have been found to be attractive over a distance of at least 5-10 m depending on the insect species (Lee, 2010). ...
... Currently, it is unknown whether the presence of the styrene-benzaldehyde blend would prevent parasitoid attraction towards HIPVs, the main cue to locate hosts. Previous studies, however, have found more predators and parasitoids in fields with both HIPVs and synthetic lures to attract the natural enemies than in fields with only HIPVs or host volatiles (Braasch & Kaplan, 2012;Kelly et al., 2014). Further research is needed to find out whether our styrene-benzaldehyde blend, possibly combined with a reward, would not only attract aphid parasitoids but also enhance their biocontrol efficacy. ...
Manipulation of insect foraging may provide the basis for effective insect pest control strategies. Recent laboratory and small-scale greenhouse experiments have shown that a blend of styrene and benzaldehyde is attractive to some Aphidius parasitoids, making it a good candidate for attracting and retaining these natural enemies in cropping systems. However, an appropriate dispenser type and appropriate dose for field application and its attraction range have yet to be identified. In this study, we performed experiments to determine an appropriate dispenser type – Omnilure® vs. low-density polyethylene (LDPE) bags – and the most suitable dose to attract Aphidius colemani Viereck (Hymenoptera: Braconidae) under commercial greenhouse conditions and to determine the maximum distance of attraction. A mixture of 10 mg styrene and 100 μg benzaldehyde was the most attractive dose for A. colemani when provided by the dispensers under greenhouse conditions. The highest percentage of parasitoids was attracted when insects were released at a distance of 0.5 m from the Omnilure dispensers. Nevertheless, compared to the solvent control the blend of styrene and benzaldehyde remained attractive over a distance of up to 5 m. The potential application of these results in novel augmentation biocontrol strategies is discussed.
... composition and quantity of blends, their emission and degradation), distances at which they are bioactive, physiological state of arthropods that are the putative volatile receivers, are all important biotic factors, and can interact with abiotic factors, such as wind speed and direction, to affect arthropod response. Moreover, these biotic and abiotic factors are constantly changing, and thus, arthropod responses are probably also dynamic (Braasch and Kaplan 2012;Kaplan 2012). Field odorscapes, i.e. the field-scale mixture of volatile plant-produced organic compounds, differ with plant species composition and time of day , and these plant volatiles appear to affect insect behaviour at the field scale Cornu et al. 2015). ...
... Field odorscapes, i.e. the field-scale mixture of volatile plant-produced organic compounds, differ with plant species composition and time of day , and these plant volatiles appear to affect insect behaviour at the field scale Cornu et al. 2015). Studies on the distances at which HIPVs are bioactive indicate that activity ranges using point-source lures or individually induced plants vary from <2 m (Mallinger et al. 2011;Rodriguez-Saona et al. 2011) to >8 m (Braasch and Kaplan 2012) to 10 m (Bernasconi Ockroy et al. 2001). Moreover, in a field study, Braasch and Kaplan (2012) reported redistribution of braconid wasps closer to HIPV lures and with reduced wasp abundance at greater distance from the lures. ...
... Studies on the distances at which HIPVs are bioactive indicate that activity ranges using point-source lures or individually induced plants vary from <2 m (Mallinger et al. 2011;Rodriguez-Saona et al. 2011) to >8 m (Braasch and Kaplan 2012) to 10 m (Bernasconi Ockroy et al. 2001). Moreover, in a field study, Braasch and Kaplan (2012) reported redistribution of braconid wasps closer to HIPV lures and with reduced wasp abundance at greater distance from the lures. These studies suggest that volatiles can influence arthropods at a field scale. ...
Natural or synthetic elicitors can affect plant physiology by stimulating direct and indirect defence responses to herbivores. For example, increased production of plant secondary metabolites, a direct response, can negatively affect herbivore survival, development and fecundity. Indirect responses include increased emission of plant volatiles that influence herbivore and natural enemy behaviour, and production of extrafloral nectar that serves as a food source for natural enemies after their arrival on induced plants. Therefore, the use of elicitors has potential for the study of basic aspects of tritrophic interactions, as well as application in biorational pest control, i.e. an ‘attract and reward’ strategy. We conducted a field study to investigate the effects of methyl jasmonate, an elicitor of plant defence responses, on three trophic levels: the plant, herbivores and natural enemies. We made exogenous applications of methyl jasmonate to transgenic cotton and measured volatile emission, extrafloral nectar production and plant performance (yield). We also assessed insect abundance, insect performance, and parasitism and predation of brown stink bug, Euschistus servus, eggs in methyl jasmonate-treated and untreated control plots. Application of methyl jasmonate increased emission of volatiles, in particular, (+)-limonene and (3E)-4,8-dimethyl-1,3,7-nonatriene, and production of extrafloral nectar, but not yield, compared with the control treatment. Despite increased volatile and extrafloral nectar production, methyl jasmonate application did not affect plant bug performance, or mortality of E. servus egg masses, and only marginally influenced insect abundance. Mortality of E. servus eggs varied over the course of the study. Overall, methyl jasmonate treatment affected cotton plant-induced responses, but not the insects that inhabit the plants. Our results were probably influenced by reduced natural enemy colonization of cotton from adjacent non-crop habitats, and subsequent low within-field population recruitment. Much remains to be learned about the effects of exogenous application of plant-produced ‘enhancers’ on the behaviour of natural enemies before crop physiology can be manipulated to enhance pest control.
... trophic level) up to at least 8 m away, both positively (by attraction) and negatively (by repellence) in soybean fields (Braasch & Kaplan, 2012). By contrast, Mallinger et al. (2011) found that such effects were more localised and ceased at 1.5 m from the source. ...
... Crops with enhanced HIPV emission levels may reduce natural enemy populations in neighbouring crops (Braasch & Kaplan, 2012). Indeed, parasitoid redistribution on a local scale (8 m) was observed after volatile lures were used, resulting in increased braconid parasitoid densities near the lure, but lower densities in plots further away from the lure (Braasch & Kaplan, 2012). ...
... Crops with enhanced HIPV emission levels may reduce natural enemy populations in neighbouring crops (Braasch & Kaplan, 2012). Indeed, parasitoid redistribution on a local scale (8 m) was observed after volatile lures were used, resulting in increased braconid parasitoid densities near the lure, but lower densities in plots further away from the lure (Braasch & Kaplan, 2012). Other arthropod taxa, however, did not show such natural enemy depletion responses, and it is unclear what the consequences will be at larger spatial scales. ...
Herbivore-induced plant volatiles (HIPVs) are an important cue used in herbivore location by carnivorous arthropods such as parasitoids. The effects of plant volatiles on parasitoids have been well characterised at small spatial scales, but little research has been done on their effects at larger spatial scales. The spatial matrix of volatiles ('volatile mosaic') within which parasitoids locate their hosts is dynamic and heterogeneous. It is shaped by the spatial pattern of HIPV-emitting plants, the concentration, chemical composition and breakdown of the emitted HIPV blends, and by environmental factors such as wind, turbulence and vegetation that affect transport and mixing of odour plumes. The volatile mosaic may be exploited differentially by different parasitoid species, in relation to species traits such as sensory ability to perceive volatiles and the physical ability to move towards the source. Understanding how HIPVs influence parasitoids at larger spatial scales is crucial for our understanding of tritrophic interactions and sustainable pest management in agriculture. However, there is a large gap in our knowledge on how volatiles influence the process of host location by parasitoids at the landscape scale. Future studies should bridge the gap between the chemical and behavioural ecology of tritrophic interactions and landscape ecology.
... Temporal and spatial relationships between pests and natural enemies are important to consider when developing volatile lures to support biological control programs (Braasch and Kaplan 2012). In our system, the two key pests co-occur and congregate on asparagus field edges, post-harvest, while natural enemies are primarily found in the field margins, ~10 m outside the field Szendrei 2013, Ingrao et al. 2017). ...
... While the bioactive range of plant volatile lures is variable (Mallinger et al. 2011, Rodriguez-Saona et al. 2011, Braasch and Kaplan 2012, our findings indicate that the concentration of volatiles emitted by lures against the natural background of plant volatiles can have an impact on the abundance of natural enemies (Dicke et al. 2003, Schröder and. In our study, the low-density deployment of the ocimene lure was more attractive for parasitoids than when we doubled the number of lures on the field edge, suggesting that otherwise attractive plant volatiles can become repellent for insects at high concentrations (Whitman and Eller 1992, Hilker and McNeil 2008, Kaplan 2012). ...
Natural enemies can be important regulators of pests in agroecosystems, and they often rely on volatile chemical cues to find hosts. Herbivore-induced plant volatiles (HIPVs) have been a focal point in many studies that seek to increase the efficacy of biological control programs by increasing recruitment and retention of natural enemies. Our research sought to explore the role of HIPVs in asparagus agroecosystems to answer the following questions: 1) What is the composition of HIPV produced by asparagus ferns following feeding by a chewing herbivore? 2) Do field deployed lures baited with synthetic asparagus HIPVs attract natural enemies? and 3) Can HIPV lures increase biological control of asparagus pests? Volatiles were field collected from the headspace of healthy asparagus ferns, mechanically damaged ferns, and ferns fed upon by asparagus beetle larvae (Crioceris asparagi L.) (Coleoptera: Chrysomelidae). We found that asparagus beetle damaged asparagus had significantly higher concentrations of (E)-β-ocimene, (E,E)-α-farnesene, and (1)-tetradecanol than healthy or mechanically damaged ferns. Field experiments demonstrated that lures baited with isolates of ocimene and farnesene attracted parasitoids without attracting pests, but had no impact on predator recruitment. Finally, we determined that overall parasitism rates were not increased by synthetic HIPV lures but found evidence that lures may increase parasitism of asparagus miner (Ophiomyia simplex Loew) (Diptera: Agromyzidae) by pteromalids.
... Flying insects can detect and track (Beyaert & Hilker, 2014) within a certain attraction radius (Braasch & Kaplan, 2012) influenced by plant architecture (Verdeny-Vilalta, Aluja, & Casas, 2015). ...
... A synthetic herbivore-induced VOC in soybean fields attracted (or repelled) arthropods in a radius of c. 8 m (Braasch & Kaplan, 2012), while pheromone traps attracted the rice borer, Eoreuma loftini, from 50 to 100 m (Wilson, Beuzelin, Allison, & Reagan, 2016). This spatial scale of attraction, at 10's of metres, represents a realistic graininess in the odour landscape for foraging mammalian herbivores to exploit. ...
Searching for food is the first critical stage of foraging, and search efficiency is enhanced when foragers use cues from foods they seek. Yet we know little about food cues used by one major group of mammals, the herbivores, a highly interactive component of most ecosystems. How herbivores forage and what disrupts this process, both have significant ecological and evolutionary consequences beyond the animals themselves.
Our aim was to investigate how free‐ranging mammalian herbivores exploit leaf odour cues to find food plants amongst a natural and complex vegetation community. Our study system comprised the native “deer equivalent” of eastern Australian forests, the swamp wallaby Wallabia bicolor , and seedlings of Eucalyptus , the foundation tree genus in these ecosystems. We quantified how foraging wallabies responded to odour cues from plants manipulated in several ways: varying the quantity of visually concealed leaves, comparing damaged vs. undamaged leaves, and whole plants vs. those with suppressed cues.
The rate of discovery of leaves by wallabies increased with odour cue magnitude, yet animals were extremely sensitive to even a tiny odour source of just a few leaves. Whole seedlings were discovered faster if their leaves were damaged. Wallabies found whole seedlings and those with suppressed visual cues equally rapidly, day and night. Seedlings with very little odour were discovered mainly by day, as nocturnal foraging success was severely disrupted.
This study shows how leaf odour attracts mammalian herbivores to food plants, enabling non‐random search for even tiny odour sources. As damaged leaves enhanced discovery, we suggest that the benefit of attracting natural enemies to invertebrate herbivores feeding on plants (potential “cry for help”) may be offset by a cost—increased browsing by mammalian herbivores. This cost should be incorporated into multi‐trophic plant–animal studies. Finally, the breakdown in capacity to find plants at night suggests substantial but unrecognized foraging costs to herbivores when abiotic factors, such as cold temperatures or pollution, reduce or degrade plant odour cues. We predict that an increasingly polluted world will alter the foraging success of mammalian herbivores, with significant ecological ramifications given that browsing can shape ecosystems.
... Because such induced VOCs frequently indicate the presence of a herbivore, they are utilized by many carnivores as cues to find their prey, a behavior that can reduce herbivore loads and thus cause 'indirect' defense of the plants [35]. Studies searching for beneficial effects of VOCs have reported multiple promising observations (Table 1 ), including enhanced recruitment of predators , parasitoids, or entomopathogenic nematodes to VOC-releasing plants [30,31,353637, enhanced parasitization rates in caterpillars that were reared close to VOC-emitting plants [38], the successful use of intercropping with plant neighbors that mimic the emission of herbivoreinduced VOCs [39] or with repellent crops to 'push' pests out of maize fields and 'pull' them into surrounding trap plants [20,40] (Figure 1), and enhanced density of parasitoids close to dispensers emitting, for example, the VOC methyl salicylate (MeSA) [24,41424344. In addition to VOCs, plants commonly attract and maintain carnivores by offering shelter (such as domatia in the form of cavities or trichome tufts for ants and mites) or food rewards [such as pollen, floral nectar (FN), extrafloral nectar (EFN), and plant sap] [18]. ...
... The discovery of the above-mentioned VOCs seemed to open new possibilities for biological control [42] . These 'semiochemicals' or 'infochemicals' can be used by carnivores as hostfinding cues [18,32], and can be released artificially [41,42,44,73], or crops can be bred or transformed for their enhanced emission [27,28,747576, to attract beneficial organisms from wild populations, maintain commercially released biocontrol agents in an agricultural field, or simply repel herbivores from the target crop. However, VOC-based indirect resistance to herbivores has not been adopted in traditional plant breeding [1,27] and, despite the above-mentioned examples of successful biocontrol via plant VOCs, there are also examples of the opposite: VOCs can be used by herbivores to localize their host plants [77,78], a situation which can lead to highly counterproductive effects [26,77,79,80]. ...
Volatile compounds and extrafloral nectar are common defenses of wild plants; however, in crops they bear an as-yet underused potential for biological control of pests and diseases. Odor emission and nectar secretion are multigene traits in wild plants, and thus form difficult targets for breeding. Furthermore, domestication has changed the capacity of crops to express these traits. We propose that breeding crops for an enhanced capacity for tritrophic interactions and volatile-mediated direct resistance to herbivores and pathogens can contribute to environmentally-friendly and sustainable agriculture. Natural plant volatiles with antifungal or repellent properties can serve as direct resistance agents. In addition, volatiles mediating tritrophic interactions can be combined with nectar-based food rewards for carnivores to boost indirect plant defense.
... Plant-plant signalling has been shown to enhance the resistance of the receivers in the field at distances ranging from 60 cm to 1 m for sagebrush, lima bean and alder (Dolch & Tscharntke, 2000;Karban et al., 2006;Heil & Adame-Alvarez, 2010), although one study has reported stable recruitment of braconid wasps to phenylethyl alcohol from up to 8 m in experimental fields of soybean (Glycine max) (Braasch & Kaplan, 2012). In this context, the question arises: how long do VOCs remain stable in the atmosphere? ...
... We should also think more about the direct effects of HI-VOCs on pests and pathogens, rather than focusing completely on indirect effects. Indeed, repellence has been an important component in cases where HI-VOCs have been successfully used in agricultural setups (Hassanali et al., 2008;Braasch & Kaplan, 2012;Xiao et al., 2012) and the anti-microbial properties of HI-VOCs certainly require more attention. Wild plants do not rely on one isolated defence strategy and biocontrol should follow their example. ...
Plants respond to mechanical wounding, herbivore feeding or infection by pathogens with the release of volatiles. Small C6 molecules termed green-leaf volatiles form a general element in most of these blends; however, the overall composition is usually sufficiently specific that other organisms are able to determine the nature of the attacker. Receivers of herbivore-induced volatile organic compounds (HI-VOCs) comprise distant parts of the same plant (‘within-plant signalling’), neighbouring plants (‘plant–plant signalling’), herbivores, and multiple carnivores that respond to the ‘plant's cry for help’, such as parasitoids and hyperparasitoids, entomopathogenic nematodes, and predatory mites, beetles, bugs and birds. In spite of intensive research efforts, many central questions still remain. How do plants perceive volatiles? What is the relative impact of each of the interactions with different receivers of HI-VOCs on the fitness of the emitting plant and that of the interacting organisms? How long can these compounds remain stable in the atmosphere? Why are VOC-mediated effects on herbivores and beneficial organisms not used as a common tool in sustainable agriculture? Here, I briefly summarize the ecological effects of HI-VOC perception and discuss the most pertinent questions raised by participants at the 32ndNew Phytologist Symposium in Buenos Aires.
... HIPVs are a part of the inducible defense system of plants which are released from damaged plants to the environment. These VOCs communicate that the plant is attacked by herbivores to surrounding tissue, neighboring plants, and natural enemies from a distance (Heil and Ton, 2008;Braasch and Kaplan, 2012;Ninkovic et al., 2016). Natural enemies use these signals to find good places for feeding or for their offspring. ...
Conservation biological control (CBC) is a sustainable measure for ecological intensification in agriculture to establish and maintain robust natural enemy populations. CBC is contributing to integrated pest management with reduced use of pesticides and support of native biodiversity in agroecosystems. Despite rapidly expanding research on CBC during the last decades, its application in pest management at the farm level is very limited. Here, we tested a CBC strategy in a 5-year on-farm study at three locations in East Norway. This CBC strategy combined two tools to increase biological control of aphids in spring barley; 1-ATTRACT, the application of a volatile organic compound (VOC) attractant that increases lacewing egg laying, and 2-HABITAT, the maintenance of natural border vegetation. We found that the VOC attractants recruited natural enemies and guided them to the right place at the right time from the border vegetation into the cropping area to control the aphid population efficiently and reliably. The results also showed that the VOC attractants combined with periodical maintained natural border vegetation provided a higher lacewing activity and aphid suppression than with annual sown floral buffer strips. We found that maintained natural border vegetation supported by VOC attractants provided lacewing populations that controlled aphids up to 100 m into the cropping area. Without VOC attractants we recorded lacewing activity up to 50 m from the border into the cropping area if natural border vegetation was available, and up to 25 m if no border vegetation existed. The overall results demonstrated the feasibility of this CBC approach under Norwegian farming conditions leading to the successful adoption of this CBC-strategy by the farming community.
... The hunting processes of natural enemies may be divided into long-and short-distance hunting. Among them, host plant volatiles mainly help in locating herbivore-infested plants from long distances [45]. Herbivore pheromones, or body surface info-chemicals, are key chemical clues for natural enemies to target their prey at close ranges [46]. ...
Aphidius gifuensis is the dominant parasitic natural enemy of aphids. Elucidating the molecular mechanism of host recognition of A. gifuensis would improve its biological control effect. Chemosensory proteins (CSPs) play a crucial role in insect olfactory systems and are mainly involved in host localization. In this study, a total of nine CSPs of A. gifuensis with complete open reading frames were identified based on antennal transcriptome data. Phylogenetic analysis revealed that AgifCSPs were mainly clustered into three subgroups (AgifCSP1/2/7/8, AgifCSP3/9, and AgifCSP4/5/6). AgifCSP2/5 showed high expression in the antennae of both sexes. Moreover, AgifCSP5 was found to be specifically expressed in the antennae. In addition, fluorescent binding assays revealed that AifCSP5 had greater affinities for 7 of 32 volatile odor molecules from various sources. Molecular docking and site-directed mutagenesis results revealed that the residue at which AgifCSP5 binds to these seven plant volatiles is Tyr75. Behavior tests further confirmed that trans-2-nonenal, one of the seven active volatiles in the ligand binding test, significantly attracted female adults at a relatively low concentration of 10 mg/mL. In conclusion, AgifCSP5 may be involved in locating aphid-infested crops from long distances by detecting and binding trans-2-nonenal. These findings provide a theoretical foundation for further understanding the olfactory recognition mechanisms and indirect aphid localization behavior of A. gifuensis from long distances by first identifying the host plant of aphids.
... Any changes to plant phenotype by herbivore induced responses may alter the plant interaction with other community members and thereby affect the plant fitness outcome of the induced response (Kessler and Baldwin 2004;McArt et al. 2013). The induced response may even include a spatial component allowing plants to communicate with and enhance performance of other plant individuals (Braasch and Kaplan 2012). ...
In response to herbivory, most plant species adjust their chemical and morphological phenotype to acquire induced resistance to the attacking herbivore. Induced resistance may be an optimal defence strategy that allows plants to reduce metabolic costs of resistance in the absence of herbivores, allocate resistance to the most valuable plant tissues and tailor its response to the pattern of attack by multiple herbivore species. Moreover, plasticity in resistance decreases the potential that herbivores adapt to specific plant resistance traits and need to deal with a moving target of variable plant quality. Induced resistance additionally allows plants to provide information to other community members to attract natural enemies of its herbivore attacker or inform related neighbouring plants of pending herbivore attack. Despite the clear evolutionary benefits of induced resistance in plants, crop protection strategies to herbivore pests have not exploited the full potential of induced resistance for agriculture. Here, we present evidence that induced resistance offers strong potential to enhance resistance and resilience of crops to (multi-) herbivore attack. Specifically, induced resistance promotes plant plasticity to cope with multiple herbivore species by plasticity in growth and resistance, maximizes biological control by attracting natural enemies and, enhances associational resistance of the plant stand in favour of yield. Induced resistance may be further harnessed by soil quality, microbial communities and associational resistance offered by crop mixtures. In the transition to more sustainable ecology-based cropping systems that have strongly reduced pesticide and fertilizer input, induced resistance may prove to be an invaluable trait in breeding for crop resilience.
... We moved the experimental saplings to the study site after their leaves fully developed (28th April 2020). At the study site, the experimental saplings were arranged in 10 rows of 6 saplings with a minimum distance of 5 m between them, to avoid the MeJA contamination of control trees (Sam et al. in prep;Braasch and Kaplan 2012). Half of all saplings of both species were assigned to be MeJA-sprayed, while the second half served as a control. ...
Plant-animal interactions and the plant chemical defence systems are a keystone of ecology and of particular interest because they fundamentally shape ecosystem functioning. Despite that, the factors and mechanisms driving the interactions between insectivorous predators and plants, via herbivore-induced plant volatiles—HIPVs remains to be fully understood. Insectivorous birds and arthropods can use chemical cues provided by herbivore-damaged plants, yet the specific chemical defensive traits that are involved in the interactions with predators remain unknown for many plant species. In our experiments, we compared plant volatiles of English oak (Quercus robur) and Sessile oak (Quercus petraea) saplings treated with methyl jasmonate (MeJA). We studied how the MeJA-induced plant volatiles differ between these two closely related plant species, and how it influences higher trophic taxa (e.g., predation, associated arthropod communities). Using plasticine caterpillars, we assessed attractiveness of MeJA-treated oaks (vs. control untreated oaks) for predators. Overall, in both plant species, attack attempts were significantly higher on MeJA-treated saplings compared to control saplings. Birds were responsible for the majority of attack attempts, followed by ants and other arthropods. The mean total amount of volatiles emitted by MeJA-induced saplings differed among the experimental oak species over time and repeated applications of MeJA. MeJA application had no significant effect on the abundance of arthropods. However, the mean body size of individuals of different feeding guilds was affected by MeJA treatment both negatively and positively, depending on the specific feeding guild. Overall, our study concludes that (1) the application of MeJA led to increased attractiveness of oak saplings for insectivorous predators, including invertebrates and birds; (2) MeJA-treated oak saplings emitted eight specific compounds that were not detected in control saplings and two additional compounds that were emitted at 100-fold higher levels in MeJA-treated saplings compared to control saplings; and (3) the predation rate on artificial caterpillars did not significantly differ between oak species.
... Up-, down-and cross-wind flights might also help locating patchily distributed host plants. In insects, successful olfactory location of host plant patches is known to depend, among other factors, on patch size and distance between patches, i.e. parameters that determine plant volatile quantities and the spatial dimension over which information by plant volatiles can be conveyed (Bukovinszky et al., 2005;Braasch & Kaplan, 2012;Andersson et al., 2013 and references therein). ...
Plants provide chemical cues that are specific for species, plant organs and the (a)biotic environmental conditions. Insects exploit these cues for various purposes, such as habitat and host plant location, host quality assessment, aggregation, mate finding and location of herbivorous prey. The process of sensing plant infochemicals may be described as multi‐stage filtering that starts at the surface and pores of the sensory organs, continues in the sensillum lumen, with its aqueous phase containing carrier molecules, and molecular receptors in the dendritic membranes of the actual sensory cells. This chemosensory input elicits behavioural responses to plant odour that depend on chemical background information, on habitat features determining how chemical cues travel through space, and on the physiological, as well as motivational, state of the insect. Hence, insect olfactory orientation by plant odours is mediated by a fine‐tuneable olfactory system that is continuously adjusted to the actual needs of the insect.
... V težnji po razvoju učinkovite biološke strategije pri varstvu rastlin, bo potrebno razširiti perspektivo, kjer bi lahko več pozornosti namenili neposrednim učinkom HOS na škodljivce in patogene. Repelentnost je ena izmed pomembnejših komponent v primerih, kjer so bili HOS uspešno uporabljeni pri kmetijskih poskus (Hassanali et al., 2008;Braasch & Kaplan, 2012;Xiao et al., 2012) vsekakor pa je več pozornosti potrebno nameniti tudi anti-mikrobnemu delovanju HOS. Divje rastline se pri obrambi pred škodljivimi organizmi ne zanašajo samo na eno obrambno strategijo, zato bi tudi biološko varstvo rastlin moralo slediti njihovemu vzorcu. ...
V kmetijskih ekosistemih lahko talni škodljivci
povzročijo veliko gospodarsko škodo. Za njihovo zatiranje
se največkrat uporabi kemična fitofarmacevtska sredstva, ki
pa imajo lahko tudi negativne vplive na okolje. Raziskovalci
zato preučujejo druge možnosti zatiranja tako nadzemskih
kot tudi talnih škodljivih organizmov v kmetijstvu. Gibanje
organizmov je povezano z zaznavanjem kemičnih dražljajev
iz okolja. Študije so v zadnjih letih pokazale, da se proti
kemičnim dražljajem lahko gibajo tudi naravni sovražniki
škodljivcev (entomopatogene ogorčice). Govorimo o t.i. neposredni
obrambi rastlin pred škodljivimi organizmi. Rastlina,
ki jo je napadel herbivor, začne v okolico sproščati
kemične signale, ki na naravne sovražnike povzročitelja delujejo
privabilno. Doslej je bilo identificiranih le nekaj
ključnih spojin, ki so odgovorne za posredovanje v tako imenovanih
multitrofičnih interakcijah in le nekaj genov ter
biokemičnih poti, ki so odgovorne za proizvodnjo hlapljivih
organskih snovi (HOS). Mnoge spojine ostajajo še vedno
neznane, toda identifikacija le-teh ima velik potencial za
uporabo pri varstvu rastlin. Napredki v razumevanju rastlinskih
emisij in njihove vloge pri signaliziranju predstavljajo
enega izmed novih načinov manipulacije rastlinskih
eksudatov, s katerimi bi izboljšali naravne obrambne lastnosti
rastlin.
... The endeavours to develop an efficient biological strategy for the plant protection will have to adopt a broader perspective, paying more attention to the direct effects of the VOCs on the harmful organisms and pathogens. Repulsion was an important property when VOCs were successfully used in agricultural experiments (Hassanali et al. 2008;Braasch & Kaplan 2012;Xiao et al. 2012), but the antimicrobial properties of VOCs should be given more attention. In the defence against harmful organisms, wild plants do not rely solely on one defence strategy; consequently, the biological control strategies should also follow suit. ...
Plants under herbivore attack emit mixtures of volatiles that can attract the natural enemies of the herbivores. Entomopathogenic nematodes (EPNs) are organisms that can be used in the biological control of insect pests. Recent studies have shown that the movement of EPNs is associated with the detection of chemical stimuli from the environment. To date, several compounds that are responsible for the mediation in below ground multitrophic interactions have been identified. In the review, we discuss the use of EPNs in agriculture, the role of belowground volatiles and their use in plant protection programmes.
... A faster induction at the individual plant level may be achieved through the atmosphere, especially in large plants such as trees. HIPVs additionally allow the releasing plant to communicate with other trophic levels, attracting predators and parasitoids [10]. As the emission of HIPVs occurs exclusively upon herbivory, they provide an honest cue to both specific and generalist third trophic level arthropods. ...
Upon herbivory, plants release herbivore-induced plant volatiles (HIPVs), which induce chemical defenses in the plant as well as recruit natural enemies. However, whether synthetic HIPVs can be employed to enhance biological control in a cultivated crop in the field is yet to be explored. Here we show that a biodegradable formulation loaded with induced and food-signaling volatiles can selectively recruit the common green lacewing, Chrysoperla carnea, and reduce pest population under field conditions. In apple orchards, the new formulation attracted lacewing adults over a 4-week period, which correlated well with independent assessments of the longevity of the slow-release matrix measured through chemical analyses. In barley, lacewing eggs and larvae were significantly more abundant in treated plots, whereas a significant reduction of two aphid species was measured (98.9% and 93.6% of population reduction, for Sitobion avenae and Rhopalosiphum padi, respectively). Results show the potential for semiochemical-based targeted recruitment of lacewings to enhance biological control of aphids in a field setting. Further research should enhance selective recruitment by rewarding attracted natural enemies and by optimizing the application technique.
... Hymenopteran parasitoids are key biological control agents that help to mitigate economically important pests in agricultural ecosystems (Giunti et al., 2015). As foraging for hosts is strongly correlated with reproductive performance, natural selection on this behaviour is predicted to be severe in Braasch & Kaplan, 2012;Colazza & Wajnberg, 2013;Aartsma et al., 2018). Among them, herbivore-induced plant volatiles (HIPVs) provide both reliable and detectable information for successful location of the host (Vet & Dicke, 1992;Aartsma et al., 2017). ...
1. Parasitoid females foraging for hosts rely on cues derived from the insect host, the host plant and/or their interaction, and all of these can be learned during the immature and adult stages.
2. The present study investigated the importance of rearing history on foraging behaviour of Diaeretiella rapae, an endoparasitoid often associated with aphids feeding on brassicaceous plant species.
3. Parasitoids were reared on one of the four possible combinations, comprising two brassicaceous host plant species, Brassica nigra or Raphanus sativus, and two aphid species Brevicoryne brassicae or Myzus persicae. These parasitoids were tested in a Y‐tube olfactometer and given the choice between volatiles emitted by an aphid‐infested plant (25 or 100 aphids per plant) and an uninfested control plant. The parasitoid's responses were compared when offered: (i) the same plant–aphid combination as the one on which it had been reared; (ii) the same host plant infested with the alternative aphid species; or (iii) an alternative plant with the alternative aphid species.
4. Aphid density did affect the behavioural responses to the various odour sources, but rearing history did not. Diaeretiella rapae only preferred aphid‐induced to non‐induced plant volatiles at low aphid infestation level, whereas they did not discriminate between volatiles at high aphid infestation level.
5. It is concluded that aphid‐induced volatiles of brassicaceous plants play an important role during host habitat location, but seem less important for parasitoids to locate the aphid host itself. The data are discussed in the light of manipulation of host plant defences by aphids.
... This may also apply to intraspecific variation in volatile-emission rates in plants, although we are not aware of any field electroantennogram (EAG) studies using plants as odour source. Applying vials with phenylethyl alcohol (as a synthetic volatile) led to both repellent and attractant effects on the abundance of insects from distances of at least 8 m (Braasch and Kaplan 2012). However, these studies did not assess whether a change in odour concentration influences the distance from which insects are recruited. ...
Chemical information influences the behaviour of many animals, thus affecting species interactions. Many animals forage for resources that are heterogeneously distributed in space and time, and have evolved foraging behaviour that utilizes information related to these resources. Herbivore‐induced plant volatiles (HIPVs), emitted by plants upon herbivore attack, provide information on herbivory to various animal species, including parasitoids. Little is known about the spatial scale at which plants attract parasitoids via HIPVs under field conditions and how intraspecific variation in HIPV emission affects this spatial scale. Here, we investigated the spatial scale of parasitoid attraction to two cabbage accessions that differ in relative preference of the parasitoid Cotesia glomerata when plants were damaged by Pieris brassicae caterpillars. Parasitoids were released in a field experiment with plants at distances of up to 60 m from the release site using intervals between plants of 10 or 20 m to assess parasitism rates over time and distance. Additionally, we observed host‐location behaviour of parasitoids in detail in a semi‐field tent experiment with plant spacing up to 8 m. Plant accession strongly affected successful host location in field set‐ups with 10 or 20 m intervals between plants. In the semi‐field set‐up, plant finding success by parasitoids decreased with increasing plant spacing, differed between plant accessions, and was higher for host‐infested plants than for uninfested plants. We demonstrate that parasitoids can be attracted to herbivore‐infested plants over large distances (10 m or 20 m) in the field, and that stronger plant attractiveness via HIPVs increases this distance (up to at least 20 m). Our study indicates that variation in plant traits can affect attraction distance, movement patterns of parasitoids, and ultimately spatial patterns of plant–insect interactions. It is therefore important to consider plant‐trait variation in HIPVs when studying animal foraging behaviour and multi‐trophic interactions in a spatial context.
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... Herbivoure-induced plant volatiles [29] were detected from long distances by parasitoids more efficiently than were hostderived kairomones [30] and the parasitoids preferred HIPVs produced by host plants, showing comparatively lower preference to blends of chemicals produced by genotypes of the same species [31e36]. Such preferences may be learned [37] from experience gained from previous visits to host plants and host insects for oviposition [38e40]. ...
The infestation level of two destructive lepidopteran pests, [Earias vittella (Fab.) and Helicoverpa armigera (Hübner)] and the abundance of entomophages, Trichogramma chilonis Ishii and Chrysoperla zastrowi sillemi (Esben-Peterson) were studied on 10 germplasm and 16 cultivars/hybrids of Abelmoschus esculentus (L.) under field condition. High populations of the host insects on susceptible genotypes of A. esculentus increased the foraging activities of natural enemies. Among 26 genotypes, the hybrid No. 55 was noted as highly susceptible to E. vittella and H. armigera, with mean counts per 10 plants of 16.66 and 15.40 larvae, respectively. In addition 3.00 eggs/grub of C. zastrowi sillemi were recorded and 9.33% field recovery of T. chilonis. The resistant germplasm, AE 9 was less hospitable to host insects and their entomophages. Choice test experiments were conducted in the laboratory to consider kairomonic activity of acetone extracts of various parts of highly susceptible (No. 55), susceptible (Arka Anamika) and resistant (AE 9) genotypes of A. esculentus. The tests indicated that No. 55 contained kairomone substances which enhanced the percentage parasitization by T. chilonis from 6.67 to 55.33% (1% of flower extract of No. 55) and percentage predation by C. zastrowi sillemi from 10.67 to 58.22% (1% of flower extract of No. 55) on eggs of E. vittella. Similarly, on eggs of H. armigera, the percentage of parasitism by T. chilonis and percentage of predation by C. zastrowi sillemi were enhanced from 10.67 to 65.33 and 10.67 to 68.67%, respectively. The maximum abundance of herbivoures and their entomophages in the susceptible genotype (No. 55) of A. esculentus might be due to the abundance of secondary metabolites which are favourable to the enhanced foraging activities of entomophages. A systematic isolation, identification and the synthesis of these chemical cues may lead to the development of kairomone formulations that enhance the foraging efficiency of the entomophages in A. esculentus for the successful bio-suppression of E. vittella and H. armigera.
... Herbivoure-induced plant volatiles [29] were detected from long distances by parasitoids more efficiently than were hostderived kairomones [30] and the parasitoids preferred HIPVs produced by host plants, showing comparatively lower preference to blends of chemicals produced by genotypes of the same species [31e36]. Such preferences may be learned [37] from experience gained from previous visits to host plants and host insects for oviposition [38e40]. ...
... From the plant's perspective, producing odours that attract the enemies of its herbivores has often been considered advantageous (Hare, 2011;Turlings et al., 1995). In general, plant-produced odours, such as those that are attractive from relatively large distances (Braasch & Kaplan, 2012;De Boer & Dicke, 2006;Geervliet, Ariens, Dicke, & Vet, 1998) are more easily detectable for foraging wasps than odours directly emitted by a potential host, which have evolved to be cryptic. Plant-derived odours are, on the other hand, less reliable and, as hosts may feed from more than one plant species, more variable than cues produced directly by the host. ...
Populations of herbivorous insects are naturally consumed by other predacious or predatory insect species. These entomophagous insects are thus plant-dwelling organisms that use the plant for several vital functions and are affected by plant traits at the evolutionary, organism and population levels. Many entomophagous species are used for the biological control of insect pests worldwide. The aim of this chapter is to provide an exhaustive review of mechanisms underlying the interactions between plants and entomophagous insects, including those governing life history traits at the individual level, as well as those acting on population and community structure and dynamics. We detail how properties of host-infested plants determine parasitism behaviour, development (in the case of parasitoids) and nectar consumption by adult entomophagous insects. We detail how plants respond to and benefit from natural enemies attacking insect herbivores. We also illustrate how plant architecture, the vegetation communities and their climatic correlates can influence predator and parasitoid behaviour and populations. This chapter considers the biology and ecology of the interactions and mentions some implications for the biological control of plant pests.
... In addition, natural enemy behaviour in the field is only poorly understood as our current knowledge mainly relies on laboratory studies with the application of manipulation of volatile emissions under field conditions being scarce. 97,98 However, the increasing demand for reduced pesticide usage has re-ignited interest in this field. We see several opportunities for integrating natural plant resistances in crop breeding and IPM programmes. ...
Biological control is an important ecosystem service delivered by natural enemies. Together with breeding for plant defence, it constitutes one of the most promising alternatives to pesticides for controlling herbivores in sustainable crop production. Especially induced plant defences may be promising targets in plant breeding for resistance against arthropod pests. Because they are activated upon herbivore damage, costs only incur when defence is needed. Moreover, they can be more specific than constitutive defences. Nevertheless, inducible defence traits that are harming plant pest organisms may interfere with biological control agents, such as predators and parasitoids. Despite the vast fundamental knowledge on plant defence mechanisms and their effects on natural enemies, our understanding on the feasibility of combining biological control with induced plant defence in practice is relatively poor. In this review, we focus on arthropod pest control and present the most important features of biological control with natural enemies and of induced plant defence. Furthermore, we show potential synergies and conflicts among them and finally, identify gaps and list opportunities for their combined use in crop protection. We suggest that breeders should focus on inducible resistance traits that are compatible with the natural enemies of arthropod pests, specifically traits that facilitate communities of natural enemies to build-up.
... Plant volatile kairomones are generally thought to have sampling ranges of perhaps 5-10 m [28][29][30]. Given this fact, and the argument that short-range lures have a higher probability of estimating S:W ratios near the site a wild insect is caught, AA-PE lures should offer greater chances than pheromone lures of measuring localised S:W ratios and correlating codling moth trap catches with damage in localised areas. ...
Studies were conducted in commercial apple orchards in British Columbia, Canada, to determine whether lures combining ethyl-(E,Z)-2,4-decadienoate, pear ester (PE), with either acetic acid (AA) or sex pheromone, (E,E)-8,10-dodecadien-1-ol (codlemone), might improve monitoring of codling moth, Cydia pomonella (L.), in an area-wide programme integrating sterile insect technology (SIT) and mating disruption (MD). Catches of sterile and wild codling moths were compared in apple orchards receiving weekly delivery of sterile moths (1:1 sex ratio) using white delta traps baited with either AA or PE alone, and in combination. Sterile and wild codling moths responded similarly to these kairomone lures. For each moth sex and type (sterile and wild), AA-PE lures were significantly more attractive than AA or PE alone. Bisexual catches with AA-PE lures were compared with those of commercial bisexual lures containing 3 mg of codlemone plus 3 mg of PE (Pherocon CM-DA Combo lure, Trécé Inc., Adair, OK, USA), and to catches of males with standard codlemone-loaded septa used in SIT (1 mg) and MD (10 mg) programmes, respectively. CM-DA lures caught the greatest number of sterile and wild male moths in orchards managed with SIT alone, or combined with MD, whereas AA-PE lures caught 2–3_ more females than CM-DA lures under both management systems. Sterile to wild (S:W) ratios for male versus female moths in catches with AA-PE lures were equivalent, whereas in the same orchards, male S:W ratios were significantly greater than female S:W ratios when measured with CM-DA lures. Male S:W ratios measured with CM-DA lures were similar to those with codlemone lures. CM-DA and codlemone lures appear to overestimate S:W ratios as measured by AA-PE lures, probably by attracting relatively more sterile males from long range. Using AA-PE lures to monitor codling moths in an SIT programme removes fewer functional sterile males and reduces the need for trap maintenance compared with using codlemone lures. AA-PE lures allow detection of wild female moths that may measure damage potential more accurately than detection of wild males. The short-range activity of AA-PE lures compared with that of codlemone-based lures appears to improve the ability to measure S:W ratios and the impact of SIT on population control near the site where wild moths are trapped.
... From the plant's perspective, producing odours that attract the enemies of its herbivores has often been considered advantageous (Hare, 2011;Turlings et al., 1995). In general, plant-produced odours, such as those that are attractive from relatively large distances (Braasch & Kaplan, 2012;De Boer & Dicke, 2006;Geervliet, Ariens, Dicke, & Vet, 1998) are more easily detectable for foraging wasps than odours directly emitted by a potential host, which have evolved to be cryptic. Plant-derived odours are, on the other hand, less reliable and, as hosts may feed from more than one plant species, more variable than cues produced directly by the host. ...
Populations of herbivorous insects are naturally consumed by other predacious or predatory insect species. These entomophagous insects are thus plant-dwelling organisms that use the plant for several vital functions and are affected by plant traits at the evolutionary, organism and population levels. Many entomophagous species are used for the biological control of insect pests worldwide. The aim of this chapter is to provide an exhaustive review of mechanisms underlying the interactions between plants and entomophagous insects, including those governing life history traits at the individual level, as well as those acting on population and community structure and dynamics. We detail how properties of host-infested plants determine parasitism behaviour, development (in the case of parasitoids) and nectar consumption by adult entomophagous insects. We detail how plants respond to and benefit from natural enemies attacking insect herbivores. We also illustrate how plant architecture, the vegetation communities and their climatic correlates can influence predator and parasitoid behaviour and populations. This chapter considers the biology and ecology of the interactions and mentions some implications for the biological control of plant pests.
... In addition, the distance that adult apple maggot fly respond to spheres with the five-component fruit volatile blend is still uncertain. While some research has suggested that the effective radius of attraction for a pheromone or volatile stimulus can be quite small (0.04 m; depending on release rate of device, concentration of pheromone, and identity of stimulus: e.g., Byers et al. 1989, Byers 2008, other studies have suggested that the distance of attraction can be up to 8 m away (Braasch and Kaplan 2012). This highlights the need to better understand the distance of response by adult flies to more precisely elucidate the proper spacing of attracticidal spheres in an orchard with this highly specific volatile blend. ...
Investigating the chemical ecology of agricultural systems continues to be a salient part of integrated pest management programs. Apple maggot fly, a key pest of apple in eastern North America, is a visual specialist with attraction to host fruit-mimicking cues. These cues have been incorporated into red spherical traps used for both monitoring and behaviorally based management. Incorporating generalist or specialist olfactory cues can potentially increase the overall success of this management system. The primary aim of this study was to evaluate the attractiveness of a generalist olfactory cue, ammonium carbonate, and the specialist olfactory cue, a five-component apple volatile blend, when included as a component of a red attracticidal sphere system.
Secondly, we assessed how critical it was to maintain minimal deviation from the optimal, full-round specialist visual stimulus provided by red spheres. Finally, attracticidal spheres were deployed with specialist olfactory cues in commercial apple orchards to evaluate their potential for effective management of apple maggot. Ammonium carbonate did not increase residency, feeding time, or mortality in the laboratory-based trials. Field deployment of specialist olfactory cues increased apple maggot captures on red spheres, while the generalist cue did not. Apple maggot tolerated some deviation from the optimal visual stimulus without reducing captures on red spheres. Attracticidal spheres hung in perimeter trees in orchards resulted in acceptable and statistically identical levels of control compared with standard insecticide programs used by growers. Overall, our study contributes valuable information for developing a reliable attract-and-kill system for apple maggot.
... The use of synthetic HIPV for pest control in agroecosystems is not without risk. A field study showed that application of one single HIPV common in soybean managed to repel and/or attract several arthropod species in a range of up to 8 m from the source [86]. However, the authors observed that braconids were lured from surrounding fields, resulting in a depletion of braconid communities in neighbouring fields-possibly increasing the risk of herbivore outbreaks there. ...
In contrast to constitutively emitted plant volatiles (PV), herbivore-induced plant volatiles (HIPV) are specifically emitted by plants when afflicted with herbivores. HIPV can be perceived by parasitoids and predators which parasitize or prey on the respective herbivores, including parasitic hymenoptera. HIPV act as signals and facilitate host/prey detection. They comprise a blend of compounds: main constituents are terpenoids and “green leaf volatiles.” Constitutive emission of PV is well known to be influenced by abiotic factors like temperature, light intensity, water, and nutrient availability. HIPV share biosynthetic pathways with constitutively emitted PV and might therefore likewise be affected by abiotic conditions. However, the effects of abiotic factors on HIPV-mediated biotic interactions have received only limited attention to date. HIPV being influenced by the plant’s growing conditions could have major implications for pest management. Quantitative and qualitative changes in HIPV blends may improve or impair biocontrol. Enhanced emission of HIPV may attract a larger number of natural enemies. Reduced emission rates or altered compositions, however, may render blends imperceptible to parasitoides and predators. Predicting the outcome of these changes is highly important for food production and for ecosystems affected by global climate change.
... DMNT (E)-4,8-dimethyl-1,3,7-nonatriene, MDL method detection limit between the temporal and spatial patterns of plant volatiles and the dynamic changes of insect populations in the field. To date, some reports have suggested that plant volatiles may affect the spatial distribution patterns of insects [46,47], but there is currently little knowledge and no data on the temporal and spatial patterns of plant volatiles in field ambient air. Therefore, our current work provides an opportunity to investigate potential correlations between plant volatiles in field ambient air and insect populations. ...
Determination of volatile plant compounds in field ambient air is important to understand chemical communication between plants and insects and will aid the development of semiochemicals from plants for pest control. In this study, a thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method was developed to measure ultra-trace levels of volatile plant compounds in field ambient air. The desorption parameters of TD, including sorbent tube material, tube desorption temperature, desorption time, and cold trap temperature, were selected and optimized. In GC-MS analysis, the selected ion monitoring mode was used for enhanced sensitivity and selectivity. This method was sufficiently sensitive to detect part-per-trillion levels of volatile plant compounds in field ambient air. Laboratory and field evaluation revealed that the method presented high precision and accuracy. Field studies indicated that the background odor of tea plantations contained some common volatile plant compounds, such as (Z)-3-hexenol, methyl salicylate, and (E)-ocimene, at concentrations ranging from 1 to 3400 ng m(-3). In addition, the background odor in summer was more abundant in quality and quantity than in autumn. Relative to previous methods, the TD-GC-MS method is more sensitive, permitting accurate qualitative and quantitative measurements of volatile plant compounds in field ambient air.
... Factors that influence long-distance searching and orientation of insect herbivores are not well documented, although it has been demonstrated that visual cues such as color, shape, and size play an important role (Prokopy, 1983;Renwick & Chew, 1994). At close ranges (Braasch & Kaplan, 2012), volatile cues can be used by both herbivores and their natural enemies for food and host/prey location (Vet & Dicke, 1992;Bruce et al., 2005;Dicke & Baldwin, 2010). Domestication can alter the quantity and quality of volatile organic compound emissions (Gouinguen e et al., 2001;Gols et al., 2011), and changes in the composition of herbivore-induced plant volatile (HIPV) emissions among plant varieties could affect parasitism rates (Degen et al., 2012). ...
Crop domestication is the process of artificially selecting plants to increase their suitability to human tastes and cultivated growing conditions. There is increasing evidence that crop domestication can profoundly alter interactions among plants, herbivores, and their natural enemies. However, there are few generalizable predictions on how insect herbivores and natural enemies should respond to artificial selection of specific plant traits. We reviewed the literature to determine how different insect herbivore feeding guilds and natural enemy groups (parasitoids and predators) respond to existing variation in wild and cultivated plant populations for plant traits typically targeted by domestication. Our goal was to look for broad patterns in tritrophic interactions to generate support for a range of potential outcomes from human-mediated selection. Overall, we found that herbivores benefit from directional selection on traits that have been targeted by domestication, but the effects on natural enemies were less studied and less consistent. In general, herbivores appear to mirror human preferences for higher nutritional content and larger plant structures. In contrast, the general effect of lowered plant secondary metabolites did not always influence herbivores consistently. Given that crop domestication appears to be a transformative process that fundamentally alters insect–plant interactions , we believe that a more detailed understanding of the community-wide effects of crop domesti-cation is needed to simultaneously stimulate both biological control and plant breeding efforts to enhance sustainable pest control.
... The stability and functional distance of associational resistance is another puzzling issue also when considering airborne plant volatiles in field conditions [21,31]. Because insect olfaction is believed to be remarkably sensitive [6], small changes in volatile signals may reveal or disguise a great deal of information, making volatilebased defences vulnerable to interference [19]. ...
Associational herbivore resistance is potentiated by neighbouring heterogenic plant species that impact a focal plant's attraction to herbivores or the damage that they cause. One mechanism to confer associational resistance is believed to be exposure to neighbour-emitted volatiles, the receivers of which range from intra- and interspecific neighbour plants to higher-trophic-level insects. In previous studies the passive adsorption of neighbour-emitted semivolatiles has been reported, but little is known regarding the mechanisms and ecological consequences on the receiver plant and its associated biota. To utilize volatile-based associational resistance for agricultural applications, it is imperative to know its effectiveness under varying diurnal temperatures and whether herbivore natural enemies, providing biological control, are impacted. Mimicking varying diurnal temperatures in a laboratory set-up, we assessed how the tritrophic model system Brassica oleracea var. italica (broccoli)-Plutella xylostella (crucifer specialist herbivore)-Cotesia vestalis (endoparasitoid of P. xylostella) is influenced by exposure to the natural semivolatile emitter plant Rhododendron tomentosum Harmaja.
Rhododendron tomentosum-exposed B. oleracea was less susceptible to P. xylostella oviposition at both night-time (12°C) and day-time (22°C) temperatures and less favoured and damaged by P. xylostella larvae at 12°C. Exposure did not interfere with indirect defence, i.e. attraction of the natural enemy C. vestalis on host-damaged, R. tomentosum-exposed B. oleracea under 22°C, while there was a reduction in attraction (marginal preference towards host-damaged B. oleracea) under 12°C.
The ability of R. tomentosum exposure to render associational resistance against an agriculturally important Brassica herbivore P. xylostella without severely compromising the specialist parasitoid C. vestalis host location encourages further studies on the potential of using this naturally abundant plant for biocontrol. The generality of our finding on temperature as a potential regulating mechanism for the efficacy of semivolatile emitter-based associational resistance towards specialist pest larval damage should be further studied in natural and agricultural associations. Our study emphasizes the need to develop techniques to compare volatiles at the leaf versus air interface and associate their appearance and ecological role with times of activity and level of specialisation of herbivores and their natural enemies.
... Upon damage by herbivores, plants increase their volatile production and change their odour blend composition, resulting in the emission of socalled herbivore-induced plant volatiles (HIPVs) (McCormick et al. 2012;Vet and Dicke 1992). Although less reliable than host-derived cues, HIPVs are more easily detectable (Vet et al. 1991) and can attract parasitoids from larger distances (Braasch and Kaplan 2012;Geervliet et al. 1998a). Parasitoids innately respond to the HIPVs of their hosts' food plants, and may prefer blends of certain hostinfested plant species Geervliet et al. 1996;Gols et al. 2009Gols et al. , 2011 or plant genotypes (Hoballah et al. 2002;Poelman et al. 2009) over others. ...
It is well known that many parasitic wasps use herbivore-induced plant odours (HIPVs) to locate their inconspicuous host insects, and are often able to distinguish between slight differences in plant odour composition. However, few studies have examined parasitoid foraging behaviour under (semi-)field conditions. In nature, food plants of parasitoid hosts are often embedded in non-host-plant assemblages that confer both structural and chemical complexity. By releasing both naïve and experienced Cotesia glomerata females in outdoor tents, we studied how natural vegetation surrounding Pieris brassicae-infested Sinapis arvensis and Barbarea vulgaris plants influences their foraging efficiency as well as their ability to specifically orient towards the HIPVs of the host plant species on which they previously had a positive oviposition experience. Natural background vegetation reduced the host-encounter rate of naïve C. glomerata females by 47 %. While associative learning of host plant HIPVs 1 day prior to foraging caused a 28 % increase in the overall foraging efficiency of C. glomerata, it did not reduce the negative influence of natural background vegetation. At the same time, however, females foraging in natural vegetation attacked more host patches on host-plant species on which they previously had a positive oviposition experience. We conclude that, even though the presence of natural vegetation reduces the foraging efficiency of C. glomerata, it does not prevent experienced female wasps from specifically orienting towards the host-plant species from which they had learned the HIPVs.
... However, we currently have only limited understanding of how such factors influence HIPV signaling in specific settings, although somewhat more work has explored the implications of local atmospheric conditions and habitat structure on the transmission of insect pheromones [37,39]. Furthermore, we also know relatively little about the concentrations of HIPV emissions to which receiving plants and insects are exposed in nature [26 ] or the typical and maximal distances over which HIPV mediated signaling interactions occur under field conditions [40]. We can, however, certainly infer that receivers of HIPV cues that are highly mobile, including many insect species, will benefit from the perception of such cues over greater distances than more sedentary receivers such as plants (particularly where HIPV function mainly as within-plant signals). ...
... Communication distances, like atmospheric pheromone concentration studied in mating disruption, will vary as a function of wind speed, vertical leaf area density, canopy form and other factors, 41 but recent evidence suggests that plant volatiles can operate over attraction distances as great as 8 m, as in the case of a range of arthropod taxa in soybeans. 42 Several authors have considered adequate separation to avoid interference between such plant volatile treatments to be between 10 and 35 m. 43 speeds, using 6 × 6 grids of traps, which showed lower catches in the centre of the array. 46 In another study with a forest system, effects were seen at even greater distances. ...
The identification of new attractants can present opportunities for developing mass trapping, but standard screening methods are needed to expedite this. We have developed a simple approach based on quantifying trap interference in 4 × 4 trap arrays with different spacings. We discuss results from sex pheromones in Lepidoptera (lightbrown apple moth, Epiphyas postvittana), Diptera (apple leafcurling midge, Dasineura mali), and Homoptera (citrophilous mealybug, Pseudococcus calceolariae), compared with a kairomone for New Zealand flower thrips (Thrips obscuratus).
The 25:1 ratio of catch in corner to centre traps observed at 750 D. mali traps/ha was still evident as ~5:1 at 16 traps/ha, suggesting trap interference even at such low trap densities. Trap competition for sex pheromone lures at close spacing (<5 m) was evident in 16 trap arrays of the Pseudococcus calceolariae, but less so for Epiphyas postvittana. No trap competition was observed at 4 m spacings with the kairomone for T. obscuratus.
The ratio of catch in traps in the corner : centre of a 16 trap array at different spacings offers a rapid preliminary assessment method for determining potential for mass trapping. Additional knowledge of vital rates and dispersal is needed for predicting population suppression. Our approach should have value in mass trapping development.
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... Factors that influence long-distance searching and orientation of insect herbivores are not well documented, although it has been demonstrated that visual cues such as color, shape, and size play an important role (Prokopy, 1983;Renwick & Chew, 1994). At close ranges (Braasch & Kaplan, 2012), volatile cues can be used by both herbivores and their natural enemies for food and host/prey location (Vet & Dicke, 1992;Bruce et al., 2005;Dicke & Baldwin, 2010). Domestication can alter the quantity and quality of volatile organic compound emissions (Gouinguen e et al., 2001;Gols et al., 2011), and changes in the composition of herbivore-induced plant volatile (HIPV) emissions among plant varieties could affect parasitism rates (Degen et al., 2012). ...
Crop domestication is the process of artificially selecting plants to increase their suitability to human tastes and cultivated growing conditions. There is growing evidence that crop domestication can profoundly alter interactions among plants, herbivores, and their natural enemies. However, there are relatively few predictions on how insect herbivores and natural enemies may respond to the trait variation caused by crop domestication. We reviewed the literature to determine how insect behavior and growth responds to variation of traits commonly altered by domestication. Our goal was to build a qualitative model on how insect herbivores and natural enemies respond to selection, as the first step towards guiding how to breed during the domestication process to retain traits that promote natural enemy activity. Although individual species can vary considerably in their behavior and life history strategies, this framework can provide insight on how domestication can affect species behavior and responses. Overall, we find that more studies are needed in order to accurately predict how selection on morphological and resistance traits during domestication may affect species interactions across multiple scales in agroecosystems.
... Up-, down-and cross-wind flights might also help locating patchily distributed host plants. In insects, successful olfactory location of host plant patches is known to depend, among other factors, on patch size and distance between patches, i.e. parameters that determine plant volatile quantities and the spatial dimension over which information by plant volatiles can be conveyed (Bukovinszky et al., 2005;Braasch & Kaplan, 2012;Andersson et al., 2013 and references therein). ...
Plants provide chemical cues that are specific for species, plant organs and the (a)biotic environmental conditions. Insects exploit these cues for various purposes, such as habitat and host plant location, host quality assessment, aggregation, mate finding and location of herbivorous prey. The process of sensing plant infochemicals may be described as multi-stage filtering that starts at the surface and pores of the sensory organs, continues in the sensillum lumen, with its aqueous phase containing carrier molecules, and molecular receptors in the dendritic membranes of the actual sensory cells. This chemosensory input elicits behavioural responses to plant odour that depend on chemical background information, on habitat features determining how chemical cues travel through space, and on the physiological, as well as motivational, state of the insect. Hence, insect olfactory orientation by plant odours is mediated by a fine-tuneable olfactory system that is continuously adjusted to the actual needs of the insect.
... Arrows indicate direction of influence of the respective volatiles denoted by RI (Table 2; data from Smith and Beck, 2013). distances that plant volatiles may travel (Braasch and Kaplan, 2012) and if the insect of interest is flying or walking (Webster, 2012), spatial-and landscape-level variances (Kaplan, 2012), and genetic variability of some invasive plants and thus resultant differences of volatile emissions (Mendes et al., 2011). ...
Introduction:
The technology for the collection and analysis of plant-emitted volatiles for understanding chemical cues of plant-plant, plant-insect or plant-microbe interactions has increased over the years. Consequently, the in situ collection, analysis and identification of volatiles are considered integral to elucidation of complex plant communications. Due to the complexity and range of emissions the conditions for consistent emission of volatiles are difficult to standardise.
Objective:
To discuss: evaluation of emitted volatile metabolites as a means of screening potential target- and non-target weeds/plants for insect biological control agents; plant volatile metabolomics to analyse resultant data; importance of considering volatiles from damaged plants; and use of a database for reporting experimental conditions and results.
Method:
Recent literature relating to plant volatiles and plant volatile metabolomics are summarised to provide a basic understanding of how metabolomics can be applied to the study of plant volatiles.
Results:
An overview of plant secondary metabolites, plant volatile metabolomics, analysis of plant volatile metabolomics data and the subsequent input into a database, the roles of plant volatiles, volatile emission as a function of treatment, and the application of plant volatile metabolomics to biological control of invasive weeds.
Conclusion:
It is recommended that in addition to a non-damaged treatment, plants be damaged prior to collecting volatiles to provide the greatest diversity of odours. For the model system provided, optimal volatile emission occurred when the leaf was punctured with a needle. Results stored in a database should include basic environmental conditions or treatments.
Benzenoids/phenylpropanoids, the second most diverse group of plant volatiles, exhibit significant structural diversity and play crucial roles in attracting pollinators and protecting against pathogens, insects, and herbivores. This review summarizes their complex biosynthetic pathways and regulatory mechanisms, highlighting their links to plant growth, development, hormone levels, circadian rhythms, and flower coloration. External factors like light, humidity, and temperature also influence their biosynthesis. Their ecological value is discussed, offering insights for enhancing floral scent, pollinator attraction, pest resistance, and metabolic engineering through genetic modification.
The European earwig Forficula auricularia (L.) (Dermaptera: Forficulidae) is an omnivorous insect that is considered a minor pest of stone fruit and a key predator of pests in pome fruit orchards. In many pome fruit orchards, earwigs are absent or in low abundance due to broad-spectrum spray programs and the slow recolonization rate of earwigs. Orchards in transition to organic or “selective” conventional programs often struggle to achieve effective levels of biological control, and thus, may benefit from inoculating earwigs to expedite their re-establishment. In a two-year study, we evaluated the potential for mass trapping earwigs from stone fruit using rolled cardboard traps to reduce fruit damage and provide earwigs for augmentation in pome fruit. We also tested whether a single mass release or five releases (on alternating weeks) of the same total number of earwigs in apples and pears reduced pests relative to plots where no releases occurred. Mass trapping did not decrease earwig abundance or substantially reduce fruit damage in stone fruit orchards. However, trapping was an efficient method for providing earwigs for augmentation. Earwig abundances were only increased in orchards where earwigs were previously low or absent; however, multiple orchards with varying prior levels of earwigs exhibited reductions in key pests (woolly apple aphid and pear psylla). For some other pests evaluated, plots with mass releases of earwigs had a slight trend in overall lower pest density when compared with control plots. A strategy for moving earwigs out of stone fruit orchards and into pome fruit orchards could be an effective method for augmenting orchard predator populations.
Male Cydia pomonella (L.) (Lepidoptera: Tortricidae) dispersion has largely been studied in nonmating disrupted orchards due to synthetic pheromone interference with capture in monitoring traps. Little is known about female dispersion. This study aimed to characterize male and female dispersion in mating disrupted commercial apple orchards. Sterile C. pomonella recapture data from single-trap multiple-release experiments using PHEROCON CM-DA COMBO + AA Lure-baited orange Pherocon VI delta traps was interpreted to determine pheromone-kairomone lure-baited trap effective area, trap deployment density for effective monitoring, and absolute male and female C. pomonella density in mating disrupted Washington commercial apple orchards. The maximum plume reach of the pheromone-kairomone lure in mating disrupted orchards was <5 m from the baited trap for both sexes. Maximum dispersive distances for 95% of the released C. pomonella in mating disrupted orchards were 106 and 135 m for males and females, yielding trapping areas of 3.87 and 6.16 ha, respectively. Estimates were consistent across 3 growing seasons and represent the first records of male and female dispersal distance and monitoring trap efficacy from commercial C. pomonella mating disrupted apple orchards. With relevance to commercial monitoring programs and economic thresholds in mating disrupted orchards, traps should be deployed at a density of 1 per 3-6 ha. Capture of a single male or female C. pomonella corresponds to at least 82-104 C. pomonella within the 3-6 ha trapping area. This refined C. pomonella capture interpretation in pheromone-kairomone baited traps in mating disrupted commercial apple orchards yields more precise damage estimates and assists in insecticide-use decision making.
Ornamental plant production in eastern Virginia nurseries have been greatly impacted by Systena frontalis (F.), also known as the red-headed flea beetle. With the advent of S. frontalis as a prevalent pest in the past 2 decades, baseline phenology and behavior are currently understudied within Virginia nurseries. This pest is costly to control due to insecticide expenses and loss of saleable plants. In 2021 and 2022, populations of this insect were monitored at 2 commercial nurseries in eastern Virginia in order to better understand their temporal and spatial population dynamics. Patterns that emerged indicated S. frontalis could have up to 3 generations in eastern Virginia, with peaks of adult abundance in June, late July, and late August to early September. Phenylethyl alcohol was tested as an adult attractant lure, but it was found to be ineffective under nursery conditions. Diel monitoring demonstrated these adults were most active from 1100 to 1500 h. Severity of defoliation at the leaf level increased linearly with increased density of adults, where 5 individuals defoliated up to 4% of any Hydrangea paniculata cv. 'Limelight' leaf in 1 wk under greenhouse conditions. Timing of scouting and insecticide sprays according to the adult activity peaks of the day and across the season may allow reduction in overall insecticide usage.
Herbivorous insects are predicted to have higher densities in larger patches, while their natural enemies will be more affected by the edge of these patches. In this paper, we investigate the effect of the relationship between brassica horticultural plot shape and the adjacent land use on the abundance of P. xylostella and its chances to be parasitised. Samples were collected from brassica plots during spring. Landscape metrics of the study area were estimated using Landsat images. We found a negative relationship between the pest abundance and the perimeter-to-area ratio of the brassica plot, and a positive relationship with land cover estimated from Landsat images. The proportion of parasitised immatures showed opposite relationship with the same variables. Implications of these findings are discussed.
Kairomones are chemical signals that mediate interspecific interactions beneficial to organisms that detect the cues. These attractants can be individual compounds or mixtures of herbivore-induced plant volatiles (HIPVs) or herbivore chemicals such as pheromones, i.e., chemicals mediating intraspecific communication between herbivores. Natural enemies eavesdrop on kairomones during their foraging behaviour, i.e., location of oviposition sites and feeding resources in nature. Kairomone mixtures are likely to elicit stronger olfactory responses in natural enemies than single kairomones. Kairomone-based lures are used to enhance biological control strategies via the attraction and retention of natural enemies to reduce insect pest populations and crop damage in an environmentally friendly way. In this review, we focus on ways to improve the efficiency of kairomone use in crop fields. First, we highlight kairomone sources in tri-trophic systems and discuss how these attractants are used by natural enemies searching for hosts or prey. Then we summarise examples of field application of kairomones (pheromones vs. HIPVs) in recruiting natural enemies. We highlight the need for future field studies to focus on the application of kairomone blends rather than single kairomones which currently dominate the literature on field attractants for natural enemies. We further discuss ways for improving kairomone use through attract and reward technique, olfactory associative learning, and optimisation of kairomone lure formulations. Finally, we discuss why the effectiveness of kairomone use for enhancing biological control strategies should move from demonstration of increase in the number of attracted natural enemies, to reducing pest populations and crop damage below economic threshold levels and increasing crop yield.
The glasshouse whitefly (Trialeurodes vaporariorum Westwood) is a polyphagous arthropod pest that is of particular detriment to glasshouse grown tomato (Solanum lycopersicum) across temperate regions of the world. Control of whiteflies with synthetic pesticides has resulted in the evolution of resistant genotypes and a reduction in natural enemies, thus highlighting the need for environmentally sound control strategies. Volatile organic compounds (VOCs) offer an environmentally benign alternative to synthetic chemical sprays and this study explored the use of VOCs as insect repellents and plant defence elicitors to control whiteflies on tomato in a commercial glasshouse setting. Limonene in the form of a volatile dispenser system was found to successfully repel whitefly from the target crop and increased fruit yield by 32% during a heavy whitefly infestation. Analysis of tomato herbivore induced plant volatiles (HIPVs) led us to select methyl salicylate (MeSA) as the plant elicitor and application of MeSA to un-infested tomato plants was found to successfully reduce whitefly population development and increase yield by 11%, although this difference was marginally statistically significant. Combination of these two methods was also effective but whitefly abundance in combined plots was similar to the standalone limonene treatment across the course of the experiment. All of the VOC based control methods we used had a negative impact on whitefly performance, with more pronounced effects during the first few weeks of infestation. In subsequent laboratory experiments, we found elevated peroxidase (POD) activity and a significant increase in TPX1 and PR1 transcripts in MeSA treated plants. This led us to deduce that MeSA immediately induced plant defences, rather than priming them. We did however see evidence for residual priming, as plants treated with MeSA and infested with whiteflies produced significantly higher levels of POD activity than whitefly infestation alone. Despite the fact that our treatments failed to synergise, our methods can be optimised further, and the effectiveness of the standalone treatments is promising for future studies. In particular, our repellent limonene dispensers were extremely effective at deterring whiteflies and offer a low economic cost and easy to implement whitefly control option. The methods we have used here could be incorporated into current integrated pest management (IPM) systems, a sustainable approach to pest control which will be central to our efforts to manage whitefly populations under glass in the future.
In Brazil, implementation of integrated pest management in the mid-1970s until the mid-1990s allowed to develop one of the most robust tropical agriculture systems in the world. However, at the beginning of this century, the intensification of the no-tillage cultivation system combined with multiple crops cultivated in a rotation system provided food and hosts for insects throughout the year. These two factors have been responsible for provoking pest outbreaks. In order to overcome these pest outbreaks, farmers started applying huge amounts of pesticides to arable crops. The excess of pesticides, climate changes and more restrictive laws concerning insecticide use combining with the high costs of developing new synthetic molecules, and taking into account the increase in the world’s population, have put pressure on all food production sectors to develop more sustainable tools for controlling pests. In this aspect, in the last years, scientists have put effort to develop new technologies based on semiochemicals aiming to provide more sustainable, with less cost pest control methods to farmers. In this chapter, the principles of semiochemical use for monitoring and controlling pests as well as the way in which these natural molecules work are presented and discussed.
Research on insect–plant interactions has highlighted the intricacies of constitutive and induced plant defenses. Of particular interest has been the relationship of natural enemies (especially parasitic hymenoptera) to herbivore induced changes to plants, especially their responses to herbivore induced plant volatiles (HIPVs). In recent decades this has been a fertile area for research, with elegant experiments showing that HIPVs are important in attracting natural enemies to plants. We critically appraise the application of work on HIPVs in plant–insect–natural enemy interactions. The promise of applications to improve pest management has not been forthcoming. We attribute this to a failure to include the multifaceted aspects of natural enemy–prey interactions – attraction, location, subjugation and experience. Attraction in an olfactometer by naïve parasitoids has not been translated to methodologically sound field-based estimates of higher parasitism rates. We highlight what needs to be done to better understand the information that HIPVs convey, how this is utilized by parasitoids and how a greater understanding of these interactions might lead to the development of new strategies so that this knowledge can be effectively deployed for improved pest management.
Synthetic plant volatile lures attract natural enemies, but may have non-target effects due to the multifunctional nature of volatile signals. For example, methyl salicylate (MeSA) is used to attract predators, yet also serves as a signaling hormone involved in plant pathogen defense. We investigated the consequences of deploying MeSA lures to attract predators for tomato (Solanum lycopersicum) defense against herbivores. To understand the spatial distribution of the lure's effect, we exposed tomatoes in the field to MeSA along a linear distance gradient and induced defenses by simulating feeding by hornworm caterpillars in a fully crossed factorial design (+/- MeSA, +/- herbivory). Subsequently, we analyzed activity of several defensive proteins (protease inhibitors, polyphenol oxidase, peroxidase), development of hornworm larvae (Manduca sexta), growth of fungal pathogens (Cladosporium and Alternaria), and attractiveness to herbivores and predators. Overall, MeSA-exposed plants were more resistant to both insects and pathogens. Secondary pathogen infection was reduced by 25% in MeSA exposed plants, possibly due to elevated polyphenol oxidase activity. Interestingly, we found that lures affected plant pathogen defenses equivalently across all distances (up to 4 m away) indicating that horizontal diffusion of a synthetic volatile may be greater than previously assumed. While thrips avoided colonizing hornworm- damaged tomato plants, this induced resistance was not observed upon pre-exposure to MeSA, suggesting that MeSA suppresses the repellant effect induced by herbivory. Thus, using MeSA lures in biological control may inadvertently protect crops from pathogens, but has mixed effects on plant resistance to insect herbivores.
This study reports on the attractiveness of volatile chemicals to green lacewings (Neuroptera: Chrysopidae) and flower flies (Diptera: Syrphidae) as measured by catch on yellow sticky traps within corn [Zea mays L. (Cyperales: Poaceae)] and soybean [Glycine max (L.) Merr. (Fabales: Fabaceae)] plots. Green lacewings were attracted to eugenol-baited traps in two tests in soybean plots. Follow-up testing in corn showed that catch of green lacewings was enhanced when traps were baited with eugenol, its structural analog isoeugenol, or 2-phenylethanol; trap catch of green lacewings was greater with these compounds than with structural analog, 4-alllylanisole. In a follow-up test in soybean, more green lacewings were caught on traps baited with isoeugenol than with 4-allylanisole. Catch did not differ among traps baited with eugenol, isoeugenol, or 2-phenylethanol or among those baited with eugenol, 2-phenylethanol, or the ethanol control. In a 6-wk experiment in soybean, green lacewings were attracted to eugenol-baited traps in 5 of 6 wks but to traps baited with structural analog methyl eugenol in only 1 wk. Flower flies were attracted to 2-phenylethanol in initial tests in corn and soybean plots. Subsequent testing in soybeans with 2-phenylethanol and structural analogs confirmed attraction to 2-phenylethanol and also showed attractancy of 2-phenylacetaldehyde but not benzylamine. A 6-wk test in soybean found that flower flies were also attracted to traps baited with either eugenol or methyl eugenol. This is the first report of green lacewing attraction to eugenol and isoeugenol and first report of flower fly attraction to eugenol. Structure-activity relationships among attractants and practical aspects of their use are discussed.
Plants provide chemical cues that are specific for species, plant organs, and the (a)biotic environmental conditions. Insects exploit these cues for various purposes such as habitat and host plant location, host quality assessment, aggregation, mate finding and location of herbivorous prey. The process of sensing plant infochemicals may be described as multi-stage filtering that starts at the surface and pores of the sensory organs, continues in the sensillum lumen with its aqueous phase containing carrier molecules and molecular receptors in the dendritic membranes of the actual sensory cells. This chemosensory input elicits behavioural responses to plant odour that depend on chemical background information, on habitat features determining how chemical cues travel through space, and on the physiological as well as motivational state of the insect. Hence, insect olfactory orientation by plant odours is mediated by a fine-tunable olfactory system that is continuously adjusted to the actual needs of an insect.
Podisus nigrispinus (Dallas, 1851) and Brontocoris tabidus (Signoret, 1863) (Heteroptera: Pentatomidae) bugs are predators that have been used for pest control agroforestry, including Thyrinteina arnobia (Stoll, 1782) (Lepidoptera: Geometridae). The joint use of several species of natural enemies for controlling insects is growing. However is necessary to know the effect this interaction in reproductive biology, survival and nymphal development of species, beyond knowing how these species interact to locate their prey. The objectives were to study the location of prey
Thyrinteina arnobia by P. nigrispinus and B. tabidus, the effect of the interaction between predators on nymphal development, the effect of increasing the density of P. nigrispinus on the reproductive biology of B. tabidus and vice versa, the interaction effect in survival, longevity, fecundity and life table of P. nigrispinus and B. tabaidus.For the location of the prey P. nigrispinus preferred plants infested with T. arnobia and B. tabidus. This only predator preferred plants infested with T. arnobia. The
interaction between nymphs of B. tabidus and P. nigrispinus increased nymphal period and decreased the weight of nymphs. The number of eggs, of eggs per posture, of nymphs and longevity of P. nigrispinus reduced by increasing the density female B. tabidus. The number of postures of P. nigrispinus increased with the density of B. tabidus and, even at low densities, this predator reduced the reproductive characteristics of B. tabidus. The presence of heterospecific predator affect the reproductive traits of predators. However, B. tabidus was more sensitive to
the presence of P. nigrispinus this, and the incubation of eggs and the number of nymphs per posture the only reproductive parameters not influenced. Life table parameters are influenced by the presence of heterospecific predator with the highest values for predators created by themselves. These predators interact to locate prey, with greatest benefit to P. nigrispinus. The interaction between species affect reproductive parameters, survival and nymphal development. But interaction is not able to eliminate any kind, because the nymphs reached phase adult and females only reduced oviposition. These species may be used together to control agroforestry first releasing B. tabidus and then P. nigrispinus.
Recent efforts in biological control have explored using the attractive qualities of herbivore-induced plant volatiles (HIPVs) to draw natural enemies to protect crops throughout the field. Methyl salicylate (MeSA) is a common HIPV used commercially to attract natural enemies, but is closely related to the signaling hormone salicylic acid (SA). SA is known to interfere with the jasmonic acid (JA) -signaling pathway, which is responsible for regulating defenses against chewing herbivores. We investigated the possible interaction of MeSA lures (PredaLure®) and herbivory to determine if MeSA positively or negatively affects tomato defense against herbivores. We exposed tomatoes in the field to PredaLure® for two days and then induced leaves with wounding and Manduca sexta regurgitant every 24 hours for three days. Subsequently, we measured herbivore-associated defenses, specifically proteinase inhibitors, polyphenol oxidase, and peroxidase protein activity within damaged leaves, and weight gain of Spodoptera exigua, a generalist lepidopteran. We also measured pathogen-associated defenses (SA-pathway): phenylalanine ammonia-lyase activity and growth of naturally occurring biotrophic fungal pathogens (Cladosporium and Alternaria). We found that MeSA decreased tomato resistance to chewing herbivory up to four meters downwind of the lure, but it increased resistance to pathogens, indicating cross-talk between the JA and SA pathways. We suggest that while MeSA lures may attract a broad suite of natural enemies, they decrease tomato resistance to chewing herbivores in the immediate area around the lure by interfering with the JA pathway.
Background
Herbivore-induced plant volatiles, or HIPVs, are increasingly considered as a biocontrol enhancement tool by constitutively emitting these carnivore attracting chemicals from agricultural fields. While ample data substantiate the olfactory preference of predators for HIPVs in laboratory environments, little is understood about the consequences of ‘turning crops on’ in the field. To explore the ramifications for arthropod pest management, we constructed a spatially explicit predator–prey population model that simulates a crop field releasing signals to recruit natural enemies from the surrounding landscape.ResultsField size had an overriding influence on model outcome, both isolated as a single factor and interactively shaping responses to other parameters (e.g., habituation, foraging efficiency). Predator recruitment exponentially declined with increasing field size from nearly double the baseline density in small fields (225 individuals m−2) to a mere 4% increase (130 individuals m−2) in large fields. Correspondingly, HIPVs enhanced pest consumption in small fields (ca. 50% fewer prey), while generating virtually no impact in large fields.Conclusion
Collectively, the model suggests that decreasing perimeter/core area ratio will ultimately constrain the utility of predator retention as a pest control tactic in commercial sized fields and illustrates potential consequences of the widespread commercialization of this technology in agriculture.
Augmentation biocontrol is a commercially viable pest management tactic in enclosed glasshouse environments, but is far less effective in open-field agriculture where newly released enemies rapidly disperse from release sites. We tested the potential for behavior-modifying semiochemicals to increase the retention of mass released predatory stink bugs, Podisus maculiventris Say (Hemiptera: Pentatomidae), for enhanced consumption of hornworm caterpillars, Manduca sexta L. (Lepidoptera: Sphingidae). To do so, we used controlled-release dispensers to emit the herbivore-induced plant volatile, methyl salicylate (MeSA), or P. maculiventris aggregation pheromone from tomato field plots. Overall, we recaptured ca. 17% of released individuals after 36. h. This rate, however, was significantly affected by weather (12% vs. 22% recapture in rainy vs. dry weeks, respectively) and semiochemical deployment, but only under optimal weather conditions (19% vs. 26% recapture in control vs. pheromone plots, respectively, during dry weeks). Further, we detected behavioral responses of wild P. maculiventris to semiochemical treatment with 94% of all captured adults (=84 of 89 total) found in pheromone plots. Only 24 of 567 (4%) captured stink bugs tested positive for immunomarking, suggesting that hornworm predation occurred but at a low frequency. Importantly, we documented that sentinel caterpillar prey were depleted by predators at a higher rate in stink bug augmented plots on tomato plants occurring near (<3. m from) the MeSA and pheromone lures. These data empirically demonstrate that both semiochemicals are capable of increasing pest consumption via attraction of P. maculiventris. Future work should focus on mechanisms of lure attraction and the long-term consequences of predator development in fields with elevated semiochemical emissions.
The robustness of quantitative measures of compositional dissimilarity between sites was evaluated using extensive computer simulations of species’ abundance patterns over one and two dimensional configurations of sample sites in ecological space. Robustness was equated with the strength, over a range of models, of the linear and monotonic (rank-order) relationship between the compositional dissimilarities and the corresponding Euclidean distances between sites measured in the ecological space. The range of models reflected different assumptions about species’ response curve shape, sampling pattern of sites, noise level of the data, species’ interactions, trends in total site abundance, and beta diversity of gradients.
The Kulczynski, Bray-Curtis and Relativized Manhattan measures were found to have not only a robust monotonic relationship with ecological distance, but also a robust linear (proportional) relationship until ecological distances became large. Less robust measures included Chord distance, Kendall’s coefficient, Chisquared distance, Manhattan distance, and Euclidean distance.
A new ordination method, hybrid multidimensional scaling (HMDS), is introduced that combines metric and nonmetric criteria, and so takes advantage of the particular properties of robust dissimilarity measures such as the Kulczynski measure.
The behavioral manipulation of natural enemies of pest insects has been a long standing dream among the biological control practitioners. Recent work concerning the behavior of some natural enemies of pest insects suggests that this dream may become a practical reality. Wright (1964, 1965) recognized the potential for pest management by the behavioral modification of insects through the use of non-toxic agents that modify the insects’ behavior. As stated by Wright (1965) these chemicals may effect control of a pest by inhibiting a correct response or eliciting an incorrect one. He coined the term “metarchon” for the introduced stimulus which includes chemical repellents and attractants as well as physical factors such as light and sound which interfere with the insects ability to communicate. While much effort is underway to develop methods of manipulating the pest insect, a different approach is needed for the manipulation of natural enemies. Instead of attempting to elicit an incorrect response or inhibit a correct one, the goal of entomophagous insect manipulation is to redirect or stimulate the response. The behavioral modification of certain arthropod enemies of insects through the use of chemicals has opened up new opportunities for the manipulation of these arthropods for the benefit of man. However, such an approach requires a working understanding of the behavior of entomophagous arthropods and the role played by chemicals in their behavioral patterns.
Plant volatiles provide herbivorous arthropods with information that allows them to discriminate between host and non-host plants. Volatiles may also indicate plant stress status, and natural enemies can use herbivore-induced plant volatiles as cues for prey location. Neighbouring plants may also make use of volatile cues to prepare for herbivore attack. Since both constitutive and inducible plant volatile emissions can be modified by plant breeding, the possibility exists to improve plant resistance against important pests both directly and indirectly via improved biological control. So far this approach has been tested only in the realm of research, predominantly using transgenic Arabidopsis with modified composition of terpenoids or C6 green leaf compounds. However several studies have shown that it is indeed possible both to reduce herbivory and enhance natural enemy attraction simultaneously. If such effects can be translated into increased and more stable yields in important crops, this strategy might be explored by the plant breeding industry and eventually become available to plant growers in the form of resistant cultivars. There are however ecological challenges associated with this approach, and the modified plant volatile composition should preferably be inducible specifically by the target pests, or by field application of specific elicitors based on forecasts of pest attack.
To understand the role of allelochemicals in predator-prey interactions it is not sufficient to study the behavioral responses of predator and prey. One should elucidate the origin of the allelochemicals and be aware that it may be located at another trophic level. These aspects are reviewed for predator-prey interactions in general and illustrated in detail for interactions between predatory mites and herbivorous mites. In the latter system there is behavioral and chemical evidence for the involvement of the host plant in production of volatile allelochemicals upon damage by the herbivores with the consequence of attracting predators. These volatiles not only influence predator behavior, but also prey behavior and even the attractiveness of nearby plants to predators. Herbivorous mites disperse away from places with high concentrations of the volatiles, and undamaged plants attract more predators when previously exposed to volatiles from infested conspecific plants rather than from uninfested plants. The latter phenomenon may well be an example of plant-to-plant communication. The involvement of the host plant is probably not unique to the predator-herbivore-plant system under study. It may well be widespread since it makes sense from an evolutionary point of view. If so, prospects for application in pest control are wide open. These are discussed, and it is concluded that crop protection in the future should include tactics whereby man becomes an ally to plants in their strategies to manipulate predator-prey interactions through allelochemicals.
Methyl salicylate and (-)-(1R,5S)-myrtenal stimulate specific olfactory cells in the primary rhinaria on the sixth and fifth antennal segments, respectively, of the black bean aphid.Aphis fabae. In behavioral studies employing a linear track olfactometer, both compounds were repellent toA. fabae and also inhibited attraction to volatiles from its host, broad bean (Vicia faba). Methyl salicylate is associated with secondary metabolite-based defense in plants, and the monoterpenoid (-)-(1R,5S)-myrtenal is metabolically related to (-)-(1S,5S)-α-pinene, an abundant component of defensive resins produced by gymnosperms. It is argued that these two compounds are employed byA. fabae as indicators of nutritionally unsuitable or nonhost plants.
The female parasitic waspCotesia kariyai discriminated between the volatiles of corn leaves infested by younger host larvaePseudaletia separata (first to fourth instar) and uninfested leaves in a Y-tube olfactometer; the wasps were attracted to the infested leaves. In contrast, when corn plants were infested by the later stages (fifth and sixth instar) of the armyworm, the wasps did not distinguish between infested corn leaves and uninfested corn leaves in the olfactometer. Mechanically damaged leaves were no more attractive than undamaged leaves, and host larvae or their feces were not attractive to the parasitoid. Through chemical analysis, the herbivore-induced plant volatiles were identified in the headspace of infested corn leaves. The herbivore-induced volatiles (HIVs) constituted a larger proportion of the headspace of corn leaves infested by early instar armyworms than of corn leaves infested by late instar armyworms. Application of third-instar larval regurgitant onto artificially damaged sites of leaves resulted in emission of parasitoid attractants from the leaf, whereas leaves treated with sixth-instar regurgitant did not. The function of this herbivore-stage related specificity of herbivore-induced synomones is discussed in a tritrophic context.
Evidence for field attraction by beneficial insects to synthetic herbivore-induced plant volatiles (HIPVs) is presented. Three synthetic HIPVs (methyl salicylate, (Z)-3-hexenyl acetate, (E)-4,8-dimethyl-1,3,7-nonatriene) were evaluated in a Washington state hop yard during April–October 2002 for attractiveness to beneficial insects. The predatory mirid, Deraeocoris brevis (Uhler), and the anthocorid, Orius tristicolor (White), were attracted to sticky cards baited with (E)-3-hexenyl acetate, while the geocorid, Geocoris pallens Stal., and hover flies (Syrphidae) were attracted to methyl salicylate-baited cards. The coccinellid, Stethorus punctum picipes (Casey), was attracted to both HIPVs in July and September. The (E)-4,8-dimethyl-1,3,7-nonatriene did not attract any beneficial insects. Lygus hesperus Knight, Leptothrips mali (Fitch), Anagrus spp., other Miridae, Coccinellidae, and parasitic Hymenoptera were not attracted to the three HIPVs tested. The possible exploitation of HIPVs in enhancing spring populations of beneficial insects and conservation biological control in cropping systems is discussed.
Herbivorous insects recognize and locate their hosts by detecting characteristic blends of volatile compounds these plants emit. The possibility that insects may use the same compounds in a different context as nonhost cues has received relatively little attention. Volatiles normally emitted by the host but encountered without other host volatiles could theoretically function as nonhost cues. We hypothesized that insects might show a positive response to host volatile compounds when encountered together in a blend but avoid the same volatiles when encountered individually. To test this we examined the behavioural responses of the black bean aphid, Aphis fabae, to physiologically relevant doses of volatile compounds emitted by its host, Vicia faba, which had been previously implicated in host recognition. Of 15 volatiles tested for behavioural activity, 10 caused aphids to respond negatively, suggesting they were repellent. We then made a blend comprising each of these compounds at the concentration at which they elicited the most negative behavioural response. The resultant blend elicited a positive response, suggesting it was attractive/arrestant. This demonstrated that the same volatile compounds can function as both host and nonhost cues, depending upon the context in which they are perceived. Thus, background odour context needs to be considered for successful use of behaviourally active volatile compounds in integrated pest management strategies. Furthermore, the finding that odorants are perceived differently when combined suggests that there is an emergent property of odour perception whereby discrimination of odour quality can occur according to blend properties
Thirty-two flowers of Aristolochia littoralis Parodi collected in Gainesville, FL, between 29 August and 29 September 1992 contained 349 phorid flies representing seven species of the genus Megaselia: M. scalaris (Loew), M. aurea (Aldrich), M. perdita (Malloch), and four unidentified species. Experimental evidence suggests that flies are attracted to flowers by an olfactory cue, although visual cues might be used at short range. Ninety-six percent of the flies (334) were males. The reason for this male-biased sex ratio is unknown, but it is possible that the attractive olfactory cue produced by the plant is sex-specific. At least some specimens of each Megaselia species carried clumps of pollen, suggesting that they were of an appropriate size to carry out pollination. Germination tests were conducted on seeds from 10 A. littoralis fruits. The mean germination rate for seeds from the 10 fruits was 56% (range, 4-92%).
The phorid fly, Pseudacteon tricuspis Borgmeier, has been released for biological control of red imported fire ant, Solenopis invicta Buren, in many parts of the southern United States. However, little is known about the nutritional ecology and the effects of environmental and physiological factors on lifespan of adult phorid flies under laboratory or field conditions. Here we report the effects of sugar feeding, temperature, gender, mating, and body size on longevity of P. tricuspis. Sugar availability and temperature were the two major factors influencing longevity. In general, sugar feeding increased lifespan by a factor of 2–3. Longevity of P. tricuspis was inversely related to temperature, and the greatest longevity (≈15 d) was recorded for sugar-fed flies kept at 20°C. Longevity declined from ≈15 d at 20°C to 4 d at 33°C for sugar-fed females and from 7 d at 20°C to 2 d at 33°C for sugar-starved females. Similar results were obtained for male P. tricuspis, and gender or mating did not significantly influence longevity. There was no significant difference in longevity between mated and unmated female and male flies, irrespective of diet and temperature. Gender, however, had a significant effect on wing length with females being larger than males. A positive correlation between wing length and longevity was recorded for sugar-starved female and male phorid flies kept at 20°C and for sugar-starved males kept at 28°C, but not for sugar-fed flies or flies exposed to high temperatures. These results suggest that provision of supplemental sugar sources and suitable microclimate near its release sites may enhance the success of P. tricuspis as a biological control agent.
We discuss the potential pros and cons of using importation biological control against the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae). Importation of exotic organisms for biological control is never completely risk-free, but the potential negative impacts of not achieving biological control of invasive pests may exceed the risks associated with a biological control introduction. The potential benefits of biological control include reduced insecticide use and a reduced ability of the invasive pest to impact native flora and fauna, and we outline what the scope of these benefits may be for the soybean aphid. The benefits are only accrued, however, if biological control is successful, so the likelihood of successful biological must also be assessed. Accordingly, we outline some issues relevant to predicting the success of importation biological control of the soybean aphid. We also outline the potential risks to nontarget organisms that would be associated with importation biological control of the soybean aphid. Currently, two parasitoid species, Aphelinus albipodus Hayat and Fatima (Hymenoptera: Aphelinidae) and Lipolexis gracilis Förster (Hymenoptera: Braconidae) have been imported from Asia and have passed through quarantine. We briefly review the biology and host range of these two species. A different strain of A. albipodus that was released against the Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), in the early 1990s was also found to attack the soybean aphid in the laboratory and has been redistributed from Wyoming to Minnesota and Wisconsin in field releases against the soybean aphid. We discuss our rationale for going forward with this redistribution.
1 In response to herbivore attack, maize plants (Zea mays L.) emit a specific blend of induced volatiles. Artificial damage and subsequent treatment of the damaged site with caterpillar regurgitant induces the same response. The induced volatile chemicals are known to be highly attractive to several parasitoids of herbivores in laboratory bioassays, but very limited information is available on how the plant odours affect entomophagous insects in the field.
2 Experiments were conducted to determine if induced maize volatiles attract parasitic and predatory insects under field conditions and whether they affect their spatial distribution.
3 In a preliminary field experiment with blue sticky traps near treated (damaged and treated with caterpillar regurgitant) and healthy plants, more entomophagous insects (total number of parasitic Hymenoptera, Anthocoridae and Syrphidae) were trapped near treated plants than near healthy plants.
4 In a second experiment, attraction to the induced volatiles was monitored with sticky traps placed next to treated and healthy maize plants in a regular maize field. No significant differences between the two treatments were found, but significantly more insects (parasitic wasps, thrips and anthocorid bugs) were trapped near to the top of plants than on traps placed near the mid-stem. Displacement of these insect groups within the field seemed to occur principally over the canopy, but under severe weather conditions they travelled lower in the canopy.
5 In a third experiment, the effect of induced maize odours on the spatial distribution of predators and parasitoids was investigated by placing sticky traps at different distances from healthy and treated plants. The higher catches of parasitoids near treated plants and the increased presence of these insects on the downwind side of treated plants support the notion that herbivore-induced maize odours attract natural enemies of maize pests in the field.
Changes in species composition of coral communities at South Pari and South Tikus Islands, Indonesia, were examined through six sampling occasions over the period 1981 to 1988. In addition to computation of standard univariate measures of species diversity, techniques developed for use with soft-sediment community data were applied. These included graphical descriptors (k-dominance curves) and multivariate ordinations (multidimensional scaling), together with associated non-parametric multivariate significance tests which allowed hypotheses about community change to be examined. Both univariate and graphical methods illustrated clearly the major community changes following the 1982–83 El Nio, though the multivariate techniques were more sensitive in monitoring the recovery stages in later years.
Summary. Feeding by Pieris brassicae or P. rapae caterpillars on Brussels sprouts plants induces the emission of synomones that attract natural enemies of the caterpillars, Cotesia glomerata, a generalist parasitoid, and C. rubecula, a specialist on P. rapae. Previous research on this tritrophic system has identified a large number of volatiles in the headspace of herbivore-damaged Brussels sprouts plants, and this paper addresses the question which of these volatiles are perceived by the two parasitoid species. Headspace odors from both P. brassicae- and P. rapae-damaged Brussels sprouts plants were analyzed by coupled gas chromatography electro- antennogram (GC-EAG) detection. Twenty volatiles evoked consistent EAG reactions in the antennae of both species and nineteen of these volatiles could be identified with GC-MS. One component that could not be identified due to its low concentration, evoked EAG responses in antennae of C. rubecula only. Possible consequences for searching behavior of the two parasitoid species are discussed.
The robustness of quantitative measures of compositional dissimilarity between sites was evaluated using extensive computer simulations of species' abundance patterns over one and two dimensional configurations of sample sites in ecological space. Robustness was equated with the strength over a range of models, of the linear and monotonic (rank-order) relationship between the compositional dissimilarities and the corresponding Euclidean distances between sites measured in the ecological space. The range of models reflected different assumptions about species' response curve shape, sampling pattern of sites, noise level of the data, species' interactions, trends in total site abundance, and beta diversity of gradients.The Kulczynski, Bray-Curtis and Relativized Manhattan measures were found to have not only a robust monotonic relationship with ecological distance, but also a robust linear (proportional) relationship until ecological distances became large. Less robust measures included Chord distance, Kendall's coefficient, Chisquared distance, Manhattan distance, and Euclidean distance.A new ordination method, hybrid multidimensional scaling (HMDS), is introduced that combines metric and nonmetric criteria, and so takes advantage of the particular properties of robust dissimilarity measures such as the Kulczynski measure.
Floral scent compounds of Ligustrum japonicum that affect the foraging behavior of Pieris rapae adults were examined by means of chemical analyses, electroantennogram (EAG) responses, and behavioral bioassays; the behavioral biossays consisted of two tests: reflex extension of proboscis (REP) in response to odor, and attraction to scented and unscented artificial flowers. More than 30 compounds, including 2-phenylethanol, benzyl alcohol, and methyl phenylacetate as the major components were identified from L. japonicum flowers. Of these, 22 compounds were tested for their effect on foraging behavior. Phenylacetaldehyde (PA), 2-phenylethanol (PE), and 6-methylhept-5-en-2-one (MHO) elicited the highest REP responses, and benzaldehyde (BA) and methyl phenylacetate (MPA) evoked intermediate REP responses. EAG responses were not necessarily correlated with REP activities; the three high-REP compounds gave only moderate EAG responses, whereas two other compounds (ethyl phenylacetate and 2-phenylethyl acetate) that released high EAG responses showed low REP activities. In two-choice behavioral bioassays, flower models scented with any one of these high-REP compounds attracted significantly more adults, while compounds with low REP activities exhibited weak or no appreciable attractiveness. This suggests that the REP responsiveness closely reflects the attractiveness of a compound and could be an effective measure in elucidating which chemical attractants are involved in flower-visiting. A synthetic blend of five floral chemicals (PA, PE, MHO, BA, and MPA) displayed an attractiveness that was comparable to that of the floral extract and was more effective in attractiveness than the compounds tested singly. Consequently, it is highly likely that the flower-visiting by P. rapae to L. japonicum is mediated largely by floral scent chemicals and that a synergistic effect of the five floral components would be most responsible for attraction of the butterfly to this flower. The present results also strongly suggest that specific floral volatiles may facilitate close-range flower location by P. rapae, could serve in part as a cue for recognizing food sources, and also be profoundly implicated in flower preference.
Electroantennograms (EAGs) were recorded from two predatory insect species, the twelve-spotted lady beetle, Coleomegilla maculata and the green lacewing, Chrysoperla carnea in response to semiochemicals emitted from one of their prey species, the pea aphid Acyrthosiphon pisum and their host plant. EAG responses were also recorded from C. maculata in response to extracts from individuals of the opposite sex and to extracts from an herbaceous plant, catnip Nepeta cataria. Extracts of catnip and two sex pheromone components of aphids, (4aS,7S,7aR)-nepetalactone and (1R,4aS,7S,7aR)-nepetalactol, elicited significant EAG responses from the antennae of both predatory species. Of 10 corn volatile compounds tested, C. carnea adults responded most strongly to 2-phenylethanol and (E)--farnesene. A significant difference in EAG response to extracts of corn leaf collections was observed between male and female C. carnea. In C. maculata, significant EAG responses were elicited by most of the tested corn volatile compounds, except -pinene and (E)-2-hexenal. The highest EAG responses were observed in response to (E)--farnesene, -terpineol, 2-phenylethanol, and -caryophyllene. Sexual differences in EAG responses of C. maculata were only found in response to 1-octen-3-ol. Male antennae of C. maculata produced significant EAG responses to extracts from conspecific females, but not to males, which indicates that some chemicals from females could be involved in sexual communication. A significant EAG response also was recorded in response to the extracts of fluids produced during reflex bleeding. Male and female antennae of both species exhibited similar dose–response curves to most of the selected compounds, although female C. maculata antennae exhibited higher thresholds in response to several compounds including -terpineol, (Z)-3-hexenol, and (4aS,7S,7aR)-nepetalactone. Field tests showed that 2-phenylethanol was highly attractive to both sexes of the two investigated species. Only C. maculata was attracted to traps baited with -terpineol.
Previous work showed that anthocorid predators aggregate around gauze cages containing Psylla-infested trees in a pear orchard. Because anthocorids responded to odor from Psylla-infested leaves in a laboratory test, it was hypothesized that these aggregative responses in the field were triggered by olfaction of compounds associated with Psylla injury. We present chemical analyses of volatiles from damaged and undamaged plants and studies on behavioral responses of anthocorid predators to compounds released by damaged plants. Leaf headspace volatiles from clean and Psylla-infested pear trees were collected on Tenax and identified by GC-MS after thermodesorption. Twelve volatiles were found exclusively in headspace samples from Psylla-infested leaves. Six were present in significantly higher quantities in samples from infested leaves: the monoterpene, (E,E)--farnesene, the phenolic, methyl salicylate, and the green leaf compounds, (Z)-3-hexen-1-yl acetate, (Z)-3-hexen-1-ol, 1-hexyl-acetate, and 1-penten-3-ol. These compounds are known to be produced by plants, and damage by pear psyllids seems to trigger their emission. Blend composition varied and was partly correlated with tree or leaf age and degree of Psylla infestation. To study whether compounds associated with leaf injury elicit olfactory responses in anthocorid predators, apple-extracted (E,E)--farnesene, synthetic methyl salicylate, and (Z)-3-hexen-1-yl acetate were offered in a Y-tube olfactometer to field-collected adult Anthocoris spp. Significant positive responses were found to both the monoterpene and the phenolic, but not to the green leaf volatile. The results lend support to the hypothesis that predator attraction to herbivore-infested pear trees is mediated by herbivory-induced plant volatiles.
In field trapping tests, the catch of Chrysoperla carnea sensu lato (Neuroptera: Chrysopidae) increased when acetic acid was added to lures with phenylacetaldehyde. The addition of methyl salicylate
to the binary mixture of phenylacetaldehyde plus acetic acid increased catches even further. The ternary blend proved to be
more attractive than β-caryophyllene, 2-phenylethanol, or 3-methyl eugenol (compounds previously described as attractants
for chrysopids) on their own, and no influence on catches was recorded when these compounds were added as fourth components
to the ternary blend. There were minimal changes in activity when (E)-cinnamaldehyde or methyl anthranylate (both evoking large responses from female or male antennae of C. carnea in this study) were added, although both compounds showed significant attraction on their own when compared to unbaited traps.
In subtractive field bioassays with the ternary mixture, it appeared that the presence of either phenylacetaldehyde or methyl
salicylate was important, whereas acetic acid was less so in the ternary mixture. The ternary blend attracted both female
and male lacewings at sites in southern, central, and northern Europe. Possible applications of a synthetic attractant for
lacewings are discussed.
We conducted three laboratory experiments to determine the effects of learning and physiological state on the foraging behavior of Microplitis croceipes (Cresson). When given a choice between host- and food-associated odors in a wind tunnel, hungry females that had experienced these two odors showed a preference for the latter whereas the well-fed females preferred the former. Intermediately fed females with ovipositional experience preferred a host-associated odor, whereas females without such experience preferred a food-associated odor. In the wind tunnel, when host- and food-plants were present, hungry females foraged for foods more than for hosts whereas well-fed females foraged for hosts. Host-searching efficiency of females decreased as they became hungry in the wind tunnel containing host plants. We conclude that M. croceipes can learn host- and food-associated odors, and respond to these odors based on their physiological state, such as hunger and ovipositional experience. The present study suggests that hunger and the availability of food are important factors affecting foraging behavior by parasitoids in nature.
Whether to invest in current or future reproduction is an important trade-off in life history evolution. For insect parasitoids, this trade-off is determined, among other factors, by the decision whether to search for hosts (immediate gain of fitness) or food (delayed fitness gains). Although host searching has been well studied, food sources, cues that parasitoids use to search for food and how insects modify their feeding behaviour have not. To address these questions, we investigated the food- and host-searching decisions made by the parasitoid Venturia canescens in both laboratory (olfactometer experiments) and field conditions (choice experiments). The wasps detected chemical cues associated with food, as well as those associated with hosts, and moved towards one or the other according to their nutritional state. Females used as food sources the same fruits that harboured hosts and detected the olfactory cues that would direct them to these fruits. Field results were consistent with those obtained in the laboratory. By integrating responses to infochemicals related to host and food, V. canescens might reduce the costs associated with food searching, so that more time and energy can be allocated to foraging for hosts. This behaviour should result in an adaptive advantage over parasitoids that incur additional costs by searching for hosts and food in different locations.
Elucidating the chemical ecology of natural enemies, herbivores and host plants is important in the development of effective and successful integrated pest management (IPM) strategies where abundance and distribution of natural enemies could be manipulated by semiochemicals for improved conservation biological control (CBC). In response to attack by herbivores, plants produce semiochemicals called Herbivore-Induced Plant Volatiles (HIPVs) which act to repel pests and attract their natural enemies. Damaged, and in some cases, intact plants may also produce volatile signals that warn other plants of impending attack. Some of these intact plants are used as intercrops in ‘push–pull’ strategies; cropping systems based on stimulo-deterrent principle, where the target crop is intercropped with herbivore repellent plants (push) while attractant plants (pull) are planted around this intercrop. The intercrop, in addition to repelling the herbivores, attracts and conserves natural enemies thereby ensuring continued suppression of the pests. This natural delivery of semiochemicals for CBC is currently being exploited by smallholder farmers in eastern Africa in the management of cereal stemborers in maize and sorghum. Synthetic HIPVs also have the potential to effectively recruit natural enemies, thereby improving CBC as has been demonstrated in a series of field experiments in vineyards and hop yards in the Pacific Northwest of the United States. Potentially, plants could be ‘turned on’ by synthetic HIPV signals, and therefore become sources of natural enemy-recruiting volatiles. With the rapid development of plant molecular biology, modification of secondary plant metabolism is also possible which could allow appropriate semiochemicals to be generated by plants at certain growth stages. By identifying the promoter sequences associated with external plant signals that induce biochemical pathways, plant defense genes could be ‘switched on’ prior to insect attack. We review recent research on ‘push–pull’ strategies and synthetic HIPVs in recruitment of beneficial arthropods and warding off pest attack.
The response of Cotesia rubecula (Hymenoptera: Braconidae) to olfactory and visual flower stimuli was tested. It was demonstrated that parasitoids can use both flower-odors and -colors during food foraging. The response of parasitoids to food-indicating stimuli depended on the hunger state of the individual. Given a choice in a Y-tube olfactometer between flower odors and odors from host-infested leaves, food-deprived individuals chose flower odors, while sugar-fed individuals preferred host associated odors. In flight chamber experiments, food-deprived parasitoids landed more often and spent more time searching on yellow targets, while sugar-fed individuals displayed a higher overall foraging activity, without reacting differentially to yellow.
Environmental monitoring and conservation evaluation in terrestrial habitats may be enhanced by the use of invertebrate inventories, but taxonomic and logistic constraints frequently encountered during conventional taxonomic treatment have greatly restricted their use. To overcome this problem we suggest that nonspecialists may be used to classify invertebrates to morphospecies without compromising scientific accuracy. To test this proposition, large pitfall and litter samples of ants, beetles, and spiders from four forest types were sorted to morphospecies by a nonspecialist and to species by specialists. These data were used to generate morphospecies and species inventories and to estimate richness (alpha diversity), and turnover (beta diversity), information frequently used in the above activities. Our results show that the estimates of richness of ants and spiders varied little between morphospecies and species inventories. Differences between estimates of beetle richness were largely influenced by errors of identification in two families, Curculionidae and Staphylinidae. But morphospecies and species inventories yielded identical ranking of forest type using richness. Turnover was assessed by sample ordination which revealed similar clusters regardless of the type of inventory. Analysis of similarities of assemblages of ants and beetles showed significant differences between all forest types. Spider assemblages showed a lower level of discrimination. The assessment of turnover was consistent among inventories but different between the major taxa. Our findings suggest that morphospecies may be used as surrogates for species in some environmental monitoring and conservation, in particular when decisions are guided by estimates of richness and the assessment of turnover.
Insect herbivory induces plant odors that attract herbivores' natural enemies. Assuming this attraction emerges from individual compounds, genetic control over odor emission of crops may provide a rationale for manipulating the distribution of predators used for pest control. However, studies on odor perception in vertebrates and invertebrates suggest that olfactory information processing of mixtures results in odor percepts that are a synthetic whole and not a set of components that could function as recognizable individual attractants. Here, we ask if predators respond to herbivore-induced attractants in odor mixtures or to odor mixture as a whole.
We studied a system consisting of Lima bean, the herbivorous mite Tetranychus urticae and the predatory mite Phytoseiulus persimilis. We found that four herbivore-induced bean volatiles are not attractive in pure form while a fifth, methyl salicylate (MeSA), is. Several reduced mixtures deficient in one component compared to the full spider-mite induced blend were not attractive despite the presence of MeSA indicating that the predators cannot detect this component in these odor mixtures. A mixture of all five HIPV is most attractive, when offered together with the non-induced odor of Lima bean. Odors that elicit no response in their pure form were essential components of the attractive mixture.
We conclude that the predatory mites perceive odors as a synthetic whole and that the hypothesis that predatory mites recognize attractive HIPV in odor mixtures is unsupported.
Volatiles from soybean leaves (Glycine max., var. Canton) were investigated to gain knowledge about these compounds for developing new methods to control phytophagous insects in soybean fields. To extract the volatiles, two methods based on analysis of the dynamic headspace were used: thermal desorption cold trap injector (TCTI) and purge and trap injector (PTI). The separation of the compounds was carried out by gas chromatography with mass spectroscopy (HRGC-MS) and Fourier-transform infrared spectroscopy (HRGC-FTIR). The most abundant compounds were represented by: (Z)-3-hexenyl-acetate, 1-hexanol, (Z)-3-hexen-1-ol and 1-octen-3-ol. The addition of an internal standard to the samples allowed semiquantitative data to be accumulated, Solid phase microextraction (SPME) was used to characterize the profile of the volatiles from homogenized soybean leaves. There were substantial differences in comparison to the profile obtained from intact leaves; this should be due to the chemical and enzymatic modifications occurring during homogenization.
1 Behavioural responses of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), to volatiles emitted from solanaceous host plants (potato and tomato), a non-host legume (soybean), and 13 synthetic blends or three individual chemicals emitted by potato plants were investigated in laboratory bioassays. 2 Both male and female CPB were attracted to volatiles emitted by mechanically damaged potato foliage, but not to mechanically damaged tomato foliage; CPB offered a choice between the two damaged solanaceous plants did not show a preference. 3 Among 16 odourous blends or individual chemical components of potato plant emissions tested, six blends were attractive, two were repellent, and eight elicited no preference in laboratory bioassays. Volatile blends containing relatively high amounts of the green leaf volatiles (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol, or the sesquiterpene β- caryophyllene, were unattractive or repellent. Minimal blends attractive to CPB were comprised of (Z)-3-hexenyl acetate (±)-linalool and methyl salicylate: the combination of all three chemicals elicited sexually dimorphic attraction of males; two component blends comprised of (Z)-3-hexenyl acetate and either (±)-linalool and methyl salicylate attracted both sexes. Individual compounds were inactive. No significant difference was noted between two attractive blends, or an attractive synthetic blend vs. mechanically damaged potato foliage. 4 These results show that CPB are attracted to blends of specific chemicals emitted by their host plants and provide a basis for the use of plant attractants as a component of integrated management of pestiferous populations.
Only substances that have a molecular weight below about 400 and an appreciable vapor pressure at room temperature can be perceived as having odor. The spectrum of odorants is thus limited to relatively small, neutral organic compounds, including undissociated acids and nitrogenous bases.1 Relatively few organic acids are sufficiently volatile to contribute to natural aromas. Acetic (vinegary), propionic (goaty), butyric (spoiled butter), and lactic (sauerkraut) acids are odorous at relatively high concentration.
Plants have evolved an elaborate arsenal of physical and chemical defenses that allow them to cope with their numerous attackers. An increasing number of studies suggest that, if properly understood, these natural plant defenses can be manipulated and exploited for the control of insect pests. We have been studying a form of indirect plant defense, whereby, in response to insect feeding, plants emit various volatile compounds that attract the natural enemies of their attackers. Using maize as our model plant, we recently found that these tritrophic interactions also occur belowground, where insects-damaged roots release attractants for entomophatogenic nematodes. The roots of many varieties of maize release the sesquiterpene (E)-b-caryophyllene when damaged by larvae of the ferocious western corn rootworm. Interestingly, most North-American maize varieties do not emit this signal. In field studies, the absence of the signal was shown to have major consequences for nematode attraction and resulted in dramatically lower nematode infection rates of pest larvae. Hence, the plants' natural defense signals show great potential for the enhancement of biological pest control. We have also found that endophytic bacteria can affect the volatile emissions to their advantage and that induced volatiles affect defense responses in neighboring plants. I will give an overview of our work in these areas with an emphasis on the possibility to manipulate volatile emissions in crop plants in order to enhance direct and indirect resistance against pests.
• Plants produce natural enemy-attracting semiochemicals known as herbivore-induced plant volatiles (HIPV) in response to herbivore damage. Deployment of synthetic HIPV in crops could enhance the biological control of pests. To test this, six HIPV [methyl salicylate (MeSA), methyl anthranilate (MeA), methyl jasmonate (MeJA), benzaldehyde (Be), cis-3-hexenyl acetate (HA), cis-hexen-1-ol (He)] in three concentrations (0.5%, 1.0% and 2.0% v/v) mixed with a vegetable oil adjuvant, Synertrol® (Organic Crop Protectants Pty Ltd, Australia), were sprayed onto winegrape, broccoli and sweet corn plants. • The relative abundance of insects within treated plots was assessed with non-attracting, transparent sticky traps at varying time intervals up to 22 days after spraying. • In the vineyard experiment, Trichogrammatidae responded to Be and MeA (0.5%) and Be (1.0%); Encyrtidae and Bethylidae responded to MeA (1.0%); Scelionidae responded to all compounds at 1.0% and 2.0%; and predatory insects responded to MeA. In sweet corn, parasitoids as a group and Encyrtidae responded to MeA (0.5%); Braconidae responded to all compounds at 0.5% and Synertrol-only; thrips responded to all compounds at 0.5% and 1.0%; while all parasitoids responded to all compounds at 0.5% and 1.0% and Synertrol-only. In broccoli, parasitoids as a group and Scelionidae responded to Be, HA, He and Synertrol-only; Trichogrammatidae responded to Be (0.5%), He (0.5% and 1.0%), MeJA (1.0%) and MeSA (0.5%); and thrips responded to all compounds at to 0.5% and 1.0%. • Significant attraction of insects occurred up to 6 days after the HIPV application, suggesting that plants may have been induced to produce endogenous volatiles that attracted insects over an extended period. • The results obtained are discussed in relation to the potential utility of synthetic HIPV to enhance the biological control of pests.
In many plants, defence systems against herbivores are induced through the octadecanoid pathway,, which may also be involved in recruiting natural enemies of herbivores. This pathway can beinduced by treating plants with jasmonic acid or by natural herbivory, and increases resistance against herbivorous insects intomato plants, in part by causing production of toxic and antinutritive proteinase inhibitors and oxidative enzymes. Herbivore-infested tomato plants release increased amounts of volatiles and attract natural enemies of the herbivores, as do other plants. The octadecanoid pathway may regulate production of these volatiles, which attract host-seeking parasitic wasps,. However, plant resistance compounds can adversely affect parasitoids as well as herbivores. It is unclear whether the combination of increased retention and/or attractiveness of parasitic wasps to induced plants and the adverse effects of plant defence compounds on both caterpillars and parasitoids results in a net increase in parasitization of herbivores feeding on induced plants.Here I show that inducing plants with jasmonic acid increases parasitism of caterpillar pests in an agricultural field twofold. Thus, elicitors of plant resistance may become useful in agriculture.
Herbivore-induced plant volatiles (HIPVs) are potent attractants for entomophagous arthropods and researchers have long speculated that HIPVs can be used to lure natural enemies into crops, reestablishing predator-prey relationships that become decoupled in disturbed agricultural habitats. This speculation has since become reality as the number of field trials investigating HIPV-mediated attraction and its consequences for pest suppression has risen dramatically over the past 10 years. Here, I provide an overview of recent field efforts to augment natural enemy populations using HIPVs, with emphasis on those studies manipulating synthetic compounds in controlled-release dispensers, and outline a prospectus for future research needs. Specifically, I review and discuss: (i) choice of compounds and release rates; (ii) functional changes in predator and parasitoid communities; (iii) non-target effects; (iv) mechanisms of attraction and prey suppression; (v) spatial- and landscape-level considerations; (vi) context-dependent responses; and (vii) temporal stability of attraction.
The fecundity of first-generation adult Pholetesor ornigis (Weed) increased when individuals were confined with flowers of creeping "Charlie" (Glechoma hederacea L.), dandelion (Taraxacum officinale Weber), and apple (Malus domesticus L.), but not with blossoms of chickweed [Stellaria media (L.) Cyrillo] or Shepherd’s purse [Capsella bursa-pastoris (L.) Medic]. Longevity of P. ornigis was little affected. The fecundity of second-generation P. ornigis increased when individuals were confined with terminal leaves of apple with honeydew of the aphid Aphis pomi DeGeer, but not when confined with terminal leaves without honeydew or with flowers of round-leaved mallow (Malva neglecta Wallr.) or red clover (Trifolium pratense L.). Longevity of P. ornigis adults also increased when they were provided with aphid honeydew. There were significant differences between the total number (oviposited and ovarian) of eggs produced by second-generation females given different food sources. Those given aphid honeydew oviposited a greater proportion of their eggs than those confined with apple leaves without honeydew or with flowers of M. neglecta or T. pratense, Adult P. ornigis fed an aqueous solution of honey (50:50, v/v) lived longest and produced more eggs than those provided with any other food source.
The green lacewing, Chrysopa oculata Say, was significantly attracted to sticky cards baited with undiluted methyl salicylate (MeSA) in an unsprayed vineyard in Washington State. During the first three weeks of the five week experiment 5–8 times as many C. oculata were trapped on MeSA-baited as on unbaited or hexane-baited cards. Diluted (10%, 1%) MeSA-baited cards did not attract C. oculata. These results are discussed with respect to a hypothesis that only lacewings with carnivorous adults are attracted to MeSA.
Methyl salicylate (MeSA) is a herbivore-induced plant volatile that has shown potential in attracting natural enemies. Here, we conducted a meta-analysis to evaluate the magnitude of natural enemy response to MeSA in the field, and tested its attractiveness to insect predators in commercial cranberry bogs. Eighteen experiments from 14 publications were used in the meta-analysis, resulting in 91 total observations. Of these, 41 documented significant attraction and the magnitude of this attraction response was not significantly different across predator and parasitoid taxa. Insect predators were monitored in cranberries using MeSA (PredaLure)-baited and unbaited yellow sticky traps. MeSA-baited traps caught greater numbers of adult hoverfly, Toxomerus marginatus, lady beetles, and green lacewings compared with unbaited traps. In another field experiment, predator abundance was monitored using traps placed near the MeSA lure (0m), as well as at 2.5, 5, and 10m away from the lure. Adult T. marginatus, the dominant predator species, showed a clear attraction to the point source but not to the other distances. In complementary studies we showed that MeSA emissions from PredaLures dropped quickly soon after deployment in the field but remained relatively high for over 4weeks; flowering, but not vegetative, vines were a primary source of MeSA in cranberries; and, exposure to PredaLures triggered elevated MeSA emissions from vegetative vines. In conclusion, we find strong evidence that insect predators are broadly attracted to MeSA in agricultural fields, including cranberries; yet, whether this behavior can be manipulated to improve biological control needs further investigation.
Electroantennogram responses (EAGs) from seven Yponomeuta species and from Adoxophyes orana were recorded during stimulation with 57 plant volatiles and leaf extracts from six host plants. Cluster analysis was applied to determine whether any grouping occurred of the response spectra of the antennae and of the response profiles to the plant volatiles. In the dendrogram of the response spectra four clusters of species groups could be distinguished. No conclusions about the taxonomic relationships were drawn from this dendrogram because of the relatively high similarity between the response spectra of the Yponomeuta species and A. orana . This similarity can be explained by these moths having food plants in common. From the response profile dendrogram no conclusions could be drawn about the number and nature of physiologically different types of olfactory cells. The leaf extracts did not evoke significantly different responses among the Yponomeuta species and A. orana . Obviously, differences in the composition of the extracts were not expressed in the EAG. The EAG responses to plant volatiles did not differ essentially between male and female moths suggesting that both sexes were equally able in detecting host plants.
RÉSUMÉ
Comparaison des électroantennogrammes de sept espèces d' Yponomeutes et d' Adoxophyes orana à des substances volatiles végétales
Les électroantennogrammes d' Yponomeuta (7 espèces) et d'Adoxophyes orana ont été enregistrés pendant la stimulation avec 57 substances volatiles et extraits foliaires de 6 plantes‐hôtes. L'analyse de la distribution a été utilisée pour déterminer si les spectres de réponses de l'antenne et les réponses aux substances volatiles présentaient un aspect contagieux. On peut distinguer 4 groupes d'espèces dans le dendrogramma des réponses. Aucune relation taxonomique ne peut être tirée de ce dendrogramme par suite de la relativement haute similarité entre les spectres des réponses des Yponomeuta et de A. orana . Cette similarité peut s'expliquer par l'identité des plantes hôtes de ces espèces. Aucune conclusion ne peut être tirée du profil des dendrogrammes sur le nombre et la nature des différents types de cellules olfactives. Les extraits de feuiles ne provoquent pas de différences significatives dans les réponses d' Yponomeuta et A. orana , les différences dans la composition des extraits n'apparaissent pas dans les AEG. Il n'y a pas de différences entre les AEG des deux sexes aux substances volatiles, ce qui laisse supposer qu'ils sont capables, tous les deux, de détecter les plantes‐hôtes.
Several volatile compounds found in cotton were tested for attractancy to the pink bollworm, Pectinophora gossypiella (Saunders). In early-season field tests of these compounds, significant numbers of the green lacewing, Chrysopa carnea Stephens were captured in Delta traps containing 2 g of caryophyllene. Caryophyllene (C15H24) is a sesquiterpene hydrocarbon that is a major component of the aroma of a cotton field. Further tests indicated that caryophyllene and β-caryophyllene, a closely related compound, were equally attractive to green lacewings. The numerous unreplicated tests subsequently conducted substantiated this attractiveness. However, the attractancy of caryophyllene appeared to diminish during the midand late season, apparently because of the competition provided by mature cotton in the field at this time. Caryophyllene is a new attractant for the green lacewing and may be a useful addition to the known feeding attractants.
The volatile compounds in the atmosphere around corn leaves were trapped on Tenax adsorbent. The material eluted from the Tenax was analyzed by capillary gas chromatography-mass spectrometry. A total of 24 compounds were identified. Major components included (Z)-3-hexenyl acetate, (Z)-3-hexenol, a sesquiterpene tentatively identified as cyclosativene, α-ylangene, an unidentified oxygenated sesquiterpene, 2-heptanone, (Z)-4-hepten-2-one, and caryophyllene. Preliminary studies were also made on the Tenax-trapped volatiles from corn husks, silks, and roots.
1 Behavioural responses of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), to volatiles emitted from solanaceous host plants (potato and tomato), a non-host legume (soybean), and 13 synthetic blends or three individual chemicals emitted by potato plants were investigated in laboratory bioassays.
2 Both male and female CPB were attracted to volatiles emitted by mechanically damaged potato foliage, but not to mechanically damaged tomato foliage; CPB offered a choice between the two damaged solanaceous plants did not show a preference.
3 Among 16 odourous blends or individual chemical components of potato plant emissions tested, six blends were attractive, two were repellent, and eight elicited no preference in laboratory bioassays. Volatile blends containing relatively high amounts of the green leaf volatiles (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol, or the sesquiterpene β- caryophyllene, were unattractive or repellent. Minimal blends attractive to CPB were comprised of (Z)-3-hexenyl acetate (±)-linalool and methyl salicylate: the combination of all three chemicals elicited sexually dimorphic attraction of males; two component blends comprised of (Z)-3-hexenyl acetate and either (±)-linalool and methyl salicylate attracted both sexes. Individual compounds were inactive. No significant difference was noted between two attractive blends, or an attractive synthetic blend vs. mechanically damaged potato foliage.
4 These results show that CPB are attracted to blends of specific chemicals emitted by their host plants and provide a basis for the use of plant attractants as a component of integrated management of pestiferous populations.
Synthetic herbivore-induced plant volatiles (HIPVs) attract arthropod natural enemies showing potential for enhancing biological control. However, HIPVs can also affect the behavior of arthropod herbivores and possibly higher-order natural enemies, potentially complicating the use of HIPVs in biological control. The aim of our work is to understand the effects of one HIPV on the abundance of arthropods at three trophic levels. Of particular interest are effects on herbivores and enemies of natural enemies. A field experiment was carried out in turnip Brassica rapa L. (Brassicaceae) (cv. Green Globe). A randomized block design was used with a treatment of synthetic methyl salicylate (MeSA), and a control consisting of the crop alone. Yellow sticky traps were used for sampling aerial brassica pests, their natural enemies and fourth trophic-level natural enemies within the crop. Our results showed that the abundance of the diamondback moth parasitoid, Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae), the brassica leafmining pest Scaptomyza flava Fallén (Diptera: Drosophilidae), and the lacewing parasitoid, Anacharis zealandica Ashmead (Hymenoptera: Figitidae), increased significantly in the MeSA-treatment compared with the controls. Significantly more D. semiclausum females were attracted to MeSA than were males. However, it still remains unclear whether it is MeSA and/or volatiles produced by induced host plants that are attractive to the arthropods. These results are highly relevant to potential future application of HIPVs in pest management, as the attraction of arthropods within ‘untargeted’ trophic-levels may disrupt trophic cascades and challenges the ideas that the deployment of synthetic HIPVs in pest management may enhance biological control.
Introduction Under laboratory conditions, many plants have been shown to respond to herbivore damage by producing volatiles that attract the natural enemies of the herbivores responsible for the damage (Vinson et al., 1987; Dicke et al., 1990; Stowe et al., 1995; Turlings et al., 1995; Sabelis et al., 2001). The list of crop plants that appear to use such volatile signals includes Lima bean (Dicke et al.. In addition, some species of trees are thought to produce volatile signals that influence the searching behaviour of natural enemies (Drukker et al., 1995; Scutareanu et al., 1997) and the whole field of volatile signalling has become one of the fastest growing areas of entomological research. Much of this research is compelling. For some systems, we are beginning to understand the biochemical pathways and molecular mechanisms by which signals pass from herbivore to plant, from the site of attack to distant plant tissues, and eventually result in volatile release (Alborn et al., 1997, 2000; Frey et al., 2000; Shen et al., 2000; Turlings et al., 2000). Even for die-hard sceptics like myself, the accumulation of evidence to support the idea that plants have the machinery to manipulate the foraging of pre-dators and parasitoids by volatile emission is becoming overwhelming (Sabelis et al., 2001). If you're expecting a caveat, here it comes; the vast majority of research on herbivore-induced volatile emission has taken place under laboratory conditions. If this area of research is to realize its potential in applied entomology, we need to expand the number of studies that explore volatile release and subsequent responses under field conditions. Interactions that can be observed using Y-tubes in climate-controlled laboratories may have little relevance when exposed to the variation in temperature, precipitation, humidity, wind speed and wind direction that typify agricultural environments (Takabayashi et al., 1994). More-over, agricultural fields are moderately complex ecosystems containing a suite of biotic and abiotic factors that vary in strength in both space and time (Hunter, 2002). When challenged with root-feeding nematodes, foliar rusts, and a summer drought, does the machinery that produces volatile signals still operate? If so, does it matter a hill of (Lima) beans to levels of defoliation or (ultimately what counts) to crop yield? The good news is that an increasing number of research-ers are taking their putative signalling systems out of doors (Khan et al., 1997; De Moraes et al., 1998; Thaler, 1999; Birkett et al., 2000; Kessler & Baldwin, 2001; Ockroy et al., 2001) and these studies are a breath of fresh air in the volatile-enemy literature. Their results, of course, generate more questions than they answer, but they have taken an important first step in adding some ecology into an area of research whose application will ultimately fail or succeed as a result of ecological interactions. Here, I provide some background on studies of herbivore-induced volatile emissions, what we have learned to date from the limited number of field trials that have taken place, and consider where future research efforts might be concentrated.
Many insect pests utilize plant volatiles for host location and untangling the mechanisms of this process can provide tools for pest management. Numerous experimental results have been published on the effect of plant volatiles on insect pests. We used a meta-analysis to summarize this knowledge and to look for patterns. Our goal was to identify herbivore and plant traits that might explain the herbivores’ behavioral response to plant volatiles in field applications. We scored a total of 374 unique plant volatile-insect herbivore interactions obtained from 34 published studies investigating 50 herbivore pest species. Attractants had a significant effect on insect herbivore abundance but repellents did not; this latter result could be a result of the comparatively small number of field studies that tested plant volatiles as repellents (3%). Females were significantly more attracted to plant volatile baits than males. The diet breadth of herbivores was independent of a behavioral response to plant volatiles, but more case studies show effects of volatiles on chewers, followed by wood-borers and sap-feeders. There are more demonstrations of attraction to plant volatiles in Lepidoptera than in Thysanoptera. The method of plant volatile application had a significant effect on herbivore abundance and increasing the number of chemicals in individual baits attracted more herbivores. The magnitude of the response of herbivores to plant volatiles in forest and agricultural habitats was similar. We explore consistent patterns and highlight areas needing research in using plant volatiles to manage insect pests.
Olfactometry showed that the response of spring migrants of the bird cherry-oat aphid, Rhopalosiphum padi (L.) (Homoptera: Aphididae), to the repellent winter host volatile methyl salicylate changes with age of the adult aphid. Between three and four days after becoming adult, and having left the winter host Prunus padus L., aphids lost their negative response to the chemical. The change in response was not associated with contact with a summer host, oats. In a settling choice bioassay, migrants avoided oats which had been exposed to volatile methyl salicylate. Aphids with removed antennal tips did not avoid the exposed plant, indicating that plant choice was influenced by cues from the plant surface. The results are discussed in relation to the use of methyl salicylate in integrated control.
Field evidence for attraction of parasitic wasps from the families Encyrtidae and Mymaridae to grapevines baited with synthetic
versions of three herbivore-induced plant volatiles (HIPV) is presented. In a replicated experiment conducted in a juice grape
vineyard, sticky cards in blocks baited with controlled-release dispensers of methyl salicylate (MeSA), methyl jasmonate (MeJA)
or (Z)-3-hexenyl acetate (HA), trapped significantly greater numbers of Metaphycus sp. (Encyrtidae) than cards in unbaited blocks during May–September. Significantly greater numbers of Anagrus spp. (Mymaridae) were trapped in MeSA and MeJA-baited blocks than in unbaited blocks, during August–September. Greater numbers
were recorded in HA-baited blocks in September only. Previous studies showed Encyrtidae and Anagrus spp. were not attracted to sticky cards baited with vials of MeSA, MeJA or HA. Possible reasons for attraction in this study
are discussed including the possibility that synthetic, gaseous HIPV from controlled-release dispensers may stimulate plants
to produce natural blends of parasitoid-attracting volatiles.
The diet of adult females of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae) includes host insects and sugar-rich foods such as nectar and honeydew. We compared the contributions of host feeding to longevity and fecundity in A. melinus females in the presence and in the absence of honey meals. First, we assessed the longevity of females that were not allowed to oviposit. While the longevity of females fed honey was significantly increased by host feeding (median ages were 30.5 days for host-fed females and 17 days for females not allowed to host feed), the lifespan of parasitoids not fed honey did not exceed 3 days for any individual and there was no effect of host feeding on longevity in this group. In the second set of experiments, we assessed the fecundity and longevity of females allowed to oviposit. We conducted two experiments, one in which honey was continuously available, and one in which honey was not available. In both experiments, daily observations were made of females that were either allowed to host feed or manually prevented from host feeding. In the presence of honey, host feeding significantly increased both fecundity and longevity, and in the absence of honey, parasitoids died within 2 days and host feeding had no significant effect on either fecundity or longevity. The lifetime fecundity of females fed honey but not hosts exceeded the initial egg complement by 60% on average. Approximately one host per day was used for host feeding whether honey was supplied or not, and each host-feeding meal contributed approximately 3.9 eggs to the lifetime fecundity of honey-fed females. In the last experiment, we compared the rate of egg resorption over a 36-h period in A. melinus females that were deprived of hosts and either fed honey or starved. While no egg resorption was detected in honey-fed females over this time period, starved females resorbed approximately 9 eggs. Thus, the availability of a sugar-rich food interacts strongly with host feeding in influencing longevity and fecundity and has a strong direct effect on egg resorption.
Simulated data, derived from descriptive models of community variation along ecological gradients, are useful for the evaluation of ordination techniques and other numerical methods for the analysis of community data. Existing approaches to the simulation of community patterns are based on restrictive assumptions, although there is evidence supporting several alternative models. Simulation studies should aim to assess the robustness of analytical techniques to variations in model properties. This paper describes a modelling procedure which encompasses most current concepts and hypotheses about the properties of community patterns. The procedure has been used to assess the comparative robustness of several ordination techniques and to examine the effectiveness of alternative coefficients of compositional dissimilarity. COMPAS, a FORTRAN 77 computer program which implements the modelling procedure, is available on application to the author.
Qualitative and quantitative differences among pear cultivars were found
in constitutive and Cacopsylla-induced volatiles, depending on
experimental treatment of the trees (i.e., uninfested and partly or
completely infested by psyllids). Blend differences were also found
between pear cultivars and wild-type pear, alder and hawthorn–the
latter trees are frequently present in pear orchard
hedgerows. ¶Interesting differences were found in the presence of methyl
salicylate and (E,E)-α-farnesene, two compounds previously found to
mediate attraction of predatory bugs towards psyllid-infested pear
trees. Methyl salicylate is expressed constitutively and is induced
systemically by infestation in the whole plant of all four cultivars.
(E,E)-α-farnesene on the other hand showed also systemic induction in
Bartlett, NY10355 and Beurré Hardy, but in partially infested Conference
trees it was induced locally, only in herbivore-damaged leaves. No
methyl salicylate or (E,E)-α-farnesene were identified in honeydew. In
field collected headspace samples of alder leaves infested by aphids and
leaf beetles we found methyl salicylate but no (E,E)-α-farnesene,
whereas in uninfested hawthorn neither were identified. Insight in the
variability of damage-related pear volatiles will have important
implications for integrated pest management in the field.
Olfactory orientation by insects may be guided by specific volatile blends released from sites where resources are present. Such blends need to be recognized against the odorous background of the habitat. The egg parasitoid Closterocerus ruforum is known to be attracted to plant volatiles induced by egg deposition of its herbivorous host, the pine sawfly Diprion pini. The parasitoid has to detect this volatile signal against a background of other pine volatiles (i.e. odour from pine without host eggs). Previous studies have shown that attractive resource-indicating odour (pine with host eggs) and nonattractive habitat odour (pine without eggs) differ only by enhanced quantities of (E)-b-farnesene in the resourceindicating odour. However, (E)-b-farnesene per se was not attractive. We studied the relevance of quantitative ratios of (E)-b-farnesene and other pine volatiles present in the habitat for parasitoid orientation by electrophysiological methods (EAG) and behavioural (olfactometer) assays. Seven of 12 terpenoid pine volatiles elicited an EAG response. In tests of the parasitoid's behavioural response to EAG-active volatiles, a blend of five components (including (E)-b-farnesene) was sufficient to attract the parasitoid but only when the ratio of (E)-b-farnesene and the other compounds matched that in odour from egg-laden pine. Since the quantities of volatiles from egg-laden and egg-free pine are not significantly different except for (E)-b-farnesene, our results show that the quantity of a resource-indicating key compound (here (E)-b-farnesene) is validated by its ratio to quantities of background volatiles emitted by both the resource and the habitat.