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Making crops cry for help
Abstract
Plants attacked by hungry herbivores can release chemicals that attract their assailants' predators. Could these responses be exploited to develop environmentally friendly pest-control strategies? John Whitfield investigates.
... Therefore, some predators and parasitoids are attracted by plant-derived volatile organic compounds (VOCs). Other volatiles are released as herbivore-induced plant volatiles (HIPVs) due to the occurrence of the 'crying for help' phenomenon (Whitfield, 2001;Gershenzon, 2007;Bruinsma and Dicke, 2008;Dicke, 2009;Dicke and Baldwin, 2010;Kaplan, 2012;Heil, 2014;Abraham et al., 2015). HIPVs are involved in multitrophic insect-plant interactions, and furthermore, the emission of HIPV signals can be detected by neighboring unaffected plants as a wake-up call (Giacomuzzi et al., 2016). ...
In this study, we present the first characterization of herbivore-induced plant volatiles (HIPVs) released from infested olive leaves. The gall midge Dasineura oleae is a specific pest of Olea europaea and endemic of the Mediterranean Basin, an area in which severe outbreaks currently occurred. Little is known about the damage caused by the pest and the relationship with its host. Since gall formation and larval feeding activity may lead to the release of specific plant volatile compounds, we investigated the volatile profiles emitted from infested plants compared with healthy plants under both laboratory and field conditions. Additionally, the volatiles emitted from mechanically damaged plants were considered. A blend of 12 volatiles was emitted from olive trees infested by D. oleae . Of these, β-copaene, β-ocimene, cosmene, unknown 1 and unknown 3 were found to be exclusively emitted in infested plants. The emission of germacrene-D, ( E , E )-α-farnesene, and ( Z , E )-α-farnesene, α-copaene, ( E )-4,8-dimethylnona-1,3,7-triene, ( E )-β-guaiene and heptadecane significantly increased in infested trees. Linalool, β-copaen-4-α-ol, β-bourbonene, β-cubebene, β-elemene, β-copaene and δ-amorphene were found only in the field trial and showed differences depending on the level of infestation and the plant stage. ( Z )-3-Hexenol, ( E )-4-oxohen-2-enal, and 2-(2-butoxyethoxy)-ethanol, were exclusively emitted from the leaves after mechanical damage. In a field trial in Italy, we also demonstrated spring synchronization between adults of D. oleae and O. europaea trees. Analyses of morphoanatomical malformations of gall leaves showed that tissue alterations occur at the spongy parenchyma causing an increase of the leaf blade thickness. We speculate that tissue alterations may lead to HIPV release, in turn potentially attracting D. oleae natural enemies.
... Volatiles released under herbivore attack are termed herbivore-induced plant volatiles (HIPVs) and can play an important role in multi-trophic interactions (Bruce 2014;Dicke and Loon 2000). Because natural enemies of pests are often attracted to plants emitting HIPVs, such denovo released compounds can potentially function as synomones, i.e. allelochemicals conveying an advantage to both the emitter and the receiver (Bruinsma & Dicke 2008;Dicke and Baldwin 2010;Gershenzon 2007;Whitfield 2001). Different families of parasitoids and predators, including parasitic wasps (Hymenoptera), hoverflies (Diptera: Syrphidae), predatory bugs (Heteroptera), ladybirds (Coleoptera: Coccinellidae), predatory mites (Mesostigmata), and green lacewings (Neuroptera: Chrysopidae) are attracted to HIPVs in the field (Turlings and Erb 2018). ...
Upon damage by herbivores, plants release herbivory-induced plant volatiles (HIPVs). To find their prey, the pest's natural enemies need to be fine-tuned to the composition of these volatiles. Whereas standard methods can be used in the identification and quantitation of HIPVs, more recently introduced techniques such as PTR-ToF-MS provide temporal patterns of the volatile release and detect additional compounds. In this study, we compared the volatile profile of apple trees infested with two aphid species, the green apple aphid Aphis pomi, and the rosy apple aphid Dysaphis plantaginea, by CLSA-GC-MS complemented by PTR-ToF-MS. Compounds commonly released in conjunction with both species include nonanal, decanal, methyl salicylate, geranyl acetone, (Z)-3-hexenyl acetate, (Z)-3-hexenyl butanoate, (Z)-3-hexenyl 2-methyl-butanoate, (E)-β-caryophyllene, β-bourbonene and (Z)-3-hexenyl benzoate. In addition, benzaldehyde and (E)-β-farnesene were exclusively associated with A. pomi, whereas linalool, (E)-4,8-dimethyl-1,3,7-nonatriene were exclusively associated with D. plantag-inea. PTR-ToF-MS additionally detected acetic acid (AA) and 2-phenylethanol (PET) in the blends of both trees attacked by aphid species. In the wind tunnel, the aphid predator, Chrysoperla carnea (Stephens), responded strongly to a blend of AA and PET, much stronger than to AA or PET alone. The addition of common and species-specific HIPVs did not increase the response to the binary blend of AA and PET. In our setup, two host-associated volatiles AA + PET appeared sufficient in the attraction of C. carnea. Our results also show the importance of combining complementary methods to decipher the odor profile associated with plants under pest attack and identify behaviourally active components for predators.
... Volatiles released under herbivore attack are termed herbivore-induced plant volatiles (HIPVs) and can play an important role in multi-trophic interactions (Bruce 2014;Dicke and Loon 2000). Because natural enemies of pests are often attracted to plants emitting HIPVs, such denovo released compounds can potentially function as synomones, i.e. allelochemicals conveying an advantage to both the emitter and the receiver (Bruinsma & Dicke 2008;Dicke and Baldwin 2010;Gershenzon 2007;Whitfield 2001). Different families of parasitoids and predators, including parasitic wasps (Hymenoptera), hoverflies (Diptera: Syrphidae), predatory bugs (Heteroptera), ladybirds (Coleoptera: Coccinellidae), predatory mites (Mesostigmata), and green lacewings (Neuroptera: Chrysopidae) are attracted to HIPVs in the field (Turlings and Erb 2018). ...
Upon damage by herbivores, plants release herbivory-induced plant volatiles (HIPVs). To find their prey, the pest’s natural enemies need to be fine-tuned to the composition of these volatiles. Whereas standard methods can be used in the identification and quantitation of HIPVs, more recently introduced techniques such as PTR-ToF–MS provide temporal patterns of the volatile release and detect additional compounds. In this study, we compared the volatile profile of apple trees infested with two aphid species, the green apple aphid Aphis pomi , and the rosy apple aphid Dysaphis plantaginea , by CLSA-GC–MS complemented by PTR-ToF–MS. Compounds commonly released in conjunction with both species include nonanal, decanal, methyl salicylate, geranyl acetone, ( Z )-3-hexenyl acetate, ( Z )-3-hexenyl butanoate, ( Z )-3-hexenyl 2-methyl-butanoate, ( E )-β-caryophyllene, β-bourbonene and ( Z )-3-hexenyl benzoate. In addition, benzaldehyde and ( E )-β-farnesene were exclusively associated with A. pomi , whereas linalool, ( E) -4,8-dimethyl-1,3,7-nonatriene were exclusively associated with D. plantaginea . PTR-ToF–MS additionally detected acetic acid (AA) and 2-phenylethanol (PET) in the blends of both trees attacked by aphid species. In the wind tunnel, the aphid predator, Chrysoperla carnea (Stephens), responded strongly to a blend of AA and PET, much stronger than to AA or PET alone. The addition of common and species-specific HIPVs did not increase the response to the binary blend of AA and PET. In our setup, two host-associated volatiles AA + PET appeared sufficient in the attraction of C. carnea. Our results also show the importance of combining complementary methods to decipher the odor profile associated with plants under pest attack and identify behaviourally active components for predators.
... Since the 1990s, when the first studies on the role of HIPVs in host search by natural enemies came out, the focus on developing semiochemical-based tactics to improve biological control has shifted to HIPVs (Dicke et al. 1990b;Whitfield 2001). Since the mechanisms underlying plant defenses triggered by arthropod herbivory or oviposition have been unraveled (Farmer et al. 1992;Mithofer and Boland 2008;Köllner et al. 2008;Erb et al. 2012;Reymond 2013), novel tactics have been developed and explored by manipulating the host plant-induced defenses. ...
It has been long known that natural enemies use chemical signals of multiple origin sources in host/prey finding. These semiochemicals are derived from host/prey and its subproducts (known as kairomones) or host/prey-plant complex, such as herbivore-induced plant volatiles (HIPVs). Strategies can exploit those chemicals, especially the volatiles as host/prey pheromones and HIPVs, to recruit and retain natural enemies in crops or optimize natural enemy foraging efficiency. Although far less studied, natural enemy pheromones can also be explored in tactics to enhance biological control efficiency. Several studies have shown that semiochemical-based tactics improve conservation and/or augmented biological control. In this chapter, I reviewed the main semiochemical-based practices to improve biological control in the literature and critically discussed their advantages and drawbacks. Given the vast literature on natural enemy behavior to host/prey and plant odors, I gave special attention to practical studies conducted in greenhouses or field conditions.
... Regarding the knowledge about the role of HIPV to natural enemies and herbivores in a agricultural context, some strategies of employing HIPVs to enhance biological control have been proposed (Whitfield 2001), which can be categorized in the following principles: exogenous application of elicitors in the plants (Thaler 1999), use of plant varieties that emit attractive HIPVs to natural enemies (Hoballah et al. 2002), release of synthetic HIPVs (James & Price 2004;Yu et al. 2008) and genetic manipulation of some genes that control volatile emission (Cortesero et al. 2000). ...
Plants emit odors that consist on important chemical cues to herbivores and their arthropod natural enemies. Plants normally release Volatile Organic Compounds (VOCs), however, when they are damaged by herbivores, they emit blends in different composition and in larger amounts, which are called Herbivore-Induced Plant Volatiles (HIPVs). HIPV emission is well-documented to be a plant defense mechanism against herbivory as it attracts herbivore natural enemies, i.e. parasitoids and predators. Herbivores often use VOCs from intact plants to locate food or oviposition site, although odors from herbivore-damaged plant can either repel or attract them. HIPV blend can vary in quantity and quality depending on herbivore and plant traits, or even physiological plant conditions, what lead to consequences on the third trophic level (herbivore natural enemies). So far, plant odors have been shown to play a central role in herbivore and natural enemy foraging as they are adapted to perceive them, especially at long distances. By the plant's perspective, attraction of herbivores is not desirable and mechanisms to be less detectable by them and more attractive to natural enemies could improve plant fitness.
... Regarding the knowledge about the role of HIPV to natural enemies and herbivores in a agricultural context, some strategies of employing HIPVs to enhance biological control have been proposed (Whitfield 2001), which can be categorized in the following principles: exogenous application of elicitors in the plants (Thaler 1999), use of plant varieties that emit attractive HIPVs to natural enemies (Hoballah et al. 2002), release of synthetic HIPVs (James & Price 2004;Yu et al. 2008) and genetic manipulation of some genes that control volatile emission (Cortesero et al. 2000). ...
Plants emit odors which consist on important chemical cues to both herbivores and their arthropod natural enemies. Plants continuously release Volatile Organic Compounds (VOCs). When damaged by herbivores, plants change considerably their scent profile by emiting Herbivore-Induced Plant Volatiles (HIPVs). HIPV emission is well-documented to be a plant defense mechanism against herbivory as it attracts herbivore natural enemies, i.e. parasitoids and predators. Herbivores often use VOCs from intact plants to locate food or oviposition site, although odors from herbivore-damaged plant can either repel or attract them. HIPV blend can vary in quantity and quality depending on herbivore and plant traits, or even physiological plant conditions, what lead to consequences on the third trophic level (herbivore natural enemies). So far, plant odors have been shown to play a central role in herbivore and natural enemy foraging as they are adapted to perceive them, especially at long distances. By the plant's perspective, attraction of herbivores is not desirable and mechanisms to be less detectable by them and more attractive to natural enemies could improve plant fitness.
... Plants under insect herbivore attack are able to defend themselves by releasing a range of chemicals that directly protect them, including alkaloids, terpenes, and phenolic compounds . They may also release chemicals that could defend them indirectly by attracting 'enemies of their enemies' (i.e., predators and/or parasitoids), a phenomenon that is described as 'crying for help' (Whitfield, 2001;Gershenzon, 2007;Bruinsma & Dicke, 2008;Dicke, 2009;Dicke & Baldwin, 2010;Kaplan, 2012). It has also been established that plants under attack from herbivorous insects are able to 'warn' their neighbours of impending danger; additionally, neighbours of plants under attack 'eavesdrop' on chemicals released by these plants and by so doing, prepare to defend themselves before they are attacked (Baldwin & Schultz, 1983;Karban et al., 2000;Baldwin et al., 2006;Heil & Silva Bueno, 2007). ...
Volatile organic compounds (VOCs) mediate communication between plants and insects. Plants under insect herbivore attack release VOCs either at the site of attack or systemically, indicating within-plant communication. Some of these VOCs, which may be induced only upon herbivore attack, recruit parasitoids and predatory insects to feed on the attacking insects. Moreover, some plants are able to ‘eavesdrop’ on herbivore-induced plant volatiles (HIPVs) to prime themselves against impending attack; such eavesdropping exemplifies plant–plant communication. In apple orchards, the beetle Melolontha melolontha L. (Coleoptera: Scarabaeidae) is an important insect pest whose larvae live and feed on roots for about 4 years. In this study, we investigated whether the feeding activity of M. melolontha larvae (1) alters the volatile profile of apple roots, (2) induces the release of HIPVs systemically in the leaves, and (3) whether infested plants communicate to neighbouring non-infested conspecifics through HIPVs. To answer these questions, we collected constitutive VOCs from intact M9 roots as well as M. melolontha larvae-damaged roots using a newly designed ‘rhizobox’, to collect root-released volatiles in situ, without damaging the plant root system. We also collected VOCs from the leaf-bearing shoots of M9 whose roots were under attack by M. melolontha larvae and from shoots of neighbouring non-infested conspecifics. Gas chromatography-mass spectrometry analysis showed that feeding activity of M. melolontha larvae induces the release of specific HIPVs; for instance, camphor was found in the roots only after larvae caused root damage. Melolontha melolontha also induced the systemic release of methyl salicylate and (E,E)-a-farnesene from the leaf-bearing shoots. Methyl salicylate and (E,E) a-farnesene were also released by the shoots of noninfested neighbouring conspecifics. These phenomena indicate the induction of specific VOCs below- and above-ground upon M. melolontha larvae feeding on apple roots as well as plant–plant communication in apple plants.
... Si se modifican dichos pulsos o mejor, si se emiten inadecuadamente estos cocteles, es posible que no exista respuesta porque el parasitoide no se encuentra metabólicamente o fisiológicamente disponible para interactuar con el insecto dañino a la planta. Por otro lado, si se pensara en plantas que como mecanismo de defensa emitieran constantemente estas mezclas, se correría el riesgo de una asociación de aprendizaje por parte de los parasitoides y depredadores, lo que conllevaría a que la señal pierda su significancia y por lo tanto sea ignorada 56 , 57 . De igual manera, habría que considerar como es realmente el control del herbívoro por parte de los depredadores y como por parte de los parasitoides. ...
... Igualmente, la emisión preventiva podría generar una asociación de aprendizaje que podría conducir a que los depredadores y parasitoides logren ignorar estas claves rápidamente. Una mejor opción sería producir variedades genéticamente modificadas que respondan de una manera contundente al ataque de plagas (Whitfield, 2001). ...
Plants produce and emit a great amounts of volatile organic compounds. Generally these volatile mixtures are composed by terpenoids, fatty acid derivatives and aromatic substances. the smell produced by plants have always been recognized for its commercial and aesthetic value it is emitted not only from its flowers and fruits, as well as vegetative tissues. But, since approximately two decades, the attention has focused on these organic volatiles, because of its influence in a vast array of interactions carrying out physiological, ecological and more recently atmospheric functions. One of the volatiles main role they are involved is that they can act like signals to other organisms, even for the same plant and they can be exported modifying the environment of the specie that release them influencing the behavior of its neighborhoods and enemies. Chemical volatiles have so many functions such as implications in plant reproduction attracting pollinators or seed dispersors, in chemical defense, repelling insects or avoiding bacterial or fungi phytopatogens colonization or employ them attracting natural enemies of herbivores, or using them like intra and inter specific messengers. Last progress on analysis techniques, molecular biology and biochemistry, have allowed elucidation of biosynthetic pathways, enzymes and genes compromised in the volatiles production and liberation, helping to understand, partially, the reason why this kind of compounds perform an their active roll in organisms relationships and even with the environment. In this review we give a general vision about different properties of plant volatiles, including the function that these compounds accomplish in several relationshisps at different levels.
... Broad spectrum pesticides kill predators and parasitoids as well as the pests and this sometimes leads to pest resurgences later in the season. In contrast, plant activators are compatible with integrated pest management (IPM) systems and even enhance biocontrol by increasing plant attractiveness to natural enemies (Dicke and Dijkman 1992;Whitfield 2001;Stout et al. 2006;Turlings and Ton 2006; Chapter 'Volatile Chemical Interaction Between Undamaged Plants: Effects at Higher Trophic Levels'). Activators of natural plant defences have thus been proposed as useful tools within IPM strategies that aim to minimise the use of toxic products (Vallad and Goodman 2004). ...
Evolutionary Ecology of Plant Signals and Toxins: A Conceptual Framework.- The Chemistry of Plant Signalling.- Plant Defense Signaling from the Underground Primes Aboveground Defenses to Confer Enhanced Resistance in a Cost-Efficient Manner.- Allelopathy and Exotic Plant Invasion.- Volatile Interaction Between Undamaged Plants: A Short Cut to Coexistence.- Volatile Chemical Interaction Between Undamaged Plants: Effects at Higher Trophic Levels.- Within-Plant Signalling by Volatiles Triggers Systemic Defences.- Volatile Interactions Between Undamaged Plants: Effects and Potential for Breeding Resistance to Aphids.- Communication in Ant-Plant Symbioses.- Photosensory Cues in Plant-Plant Interactions: Regulation and Functional Significance of Shade Avoidance Responses.- Global Atmospheric Change and Trophic Interactions: Are There Any General Responses?.- Exploiting Plant Signals in Sustainable Agriculture.- Plant Volatiles: Useful Signals to Monitor Crop Health Status in Greenhouses.
... Induced indirect defences to arthropod herbivores function by attracting predators or parasitoids at the third trophic level via the emission of specific volatile signals (synomones) released in response to feeding or egg deposition. These volatiles have been interpreted as the plant's 'cry for help' to predators or parasitoids, which then kill the herbivores and thus reduce the damage done (Dicke & Sabelis, 1992;Turlings et al., 1995;Whitfield, 2001;Hilker & Meiners, 2002;Degenhardt et al., 2003). ...
We investigated by olfactometry and feeding- and oviposition-choice-tests how the highly specialised elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), responds to conspecifically induced defences in the field elm Ulmus minor Miller (Ulmaceae). While egg deposition of the beetle induced elms to release volatiles attractive to the egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae), feeding alone did not. In the present study, females of the elm leaf beetle showed preferences for the odours of twigs induced by low egg deposition and feeding over odours from uninfested twigs. In contrast, heavy infestation rendered elm odours less attractive to the beetles. Feeding and oviposition bioassays revealed an oviposition preference for leaves from uninfested twigs when compared to locally infested leaves. However, beetles preferred to feed upon systemically induced leaves compared to uninfested ones. The different preferences of the elm leaf beetle during host plant approach might be explained by a strategy that accounts for both gaining access to high quality nutrition and avoiding competition or parasitism.
... Mean number of emerged Striga hermonthica and rice grain yields (t ha À1 ) from upland rice plots planted either as sole stands or intercropped with Desmodium uncinatum Means represent data averages of six replications, each 6 m by 6 m plots over two cropping seasons. attract natural enemies in tritrophic interactions in response to insect attack (Whitfield, 2001;Turlings and Ton, 2006), and to repel further colonization by the herbivore itself (e.g. De Moraes et al., 2001). ...
Lepidopteran stemborers and parasitic weeds in the genus Striga are major constraints to efficient production of cereals, the most important staple food crops in Africa. Smallholder farmers
are resource constrained and unable to afford expensive chemicals for crop protection. Development of a push–pull approach
for integrated pest and weed management is reviewed here. Appropriate plants were discovered that naturally emit signalling
chemicals (semiochemicals). Plants highly attractive for egg laying by stemborer pests were selected and employed as trap
crops (pull), to draw pests away from the main crop. Of these, Napier grass, Pennisetum purpureum (Schumach), despite its attractiveness, supported minimal survival of the pests’ immature stages. Plants that repelled stemborer
pests, notably molasses grass, Melinis minutiflora P. Beauv., and forage legumes in the genus Desmodium, were selected as intercrops (push). Desmodium intercrops suppress Striga hermonthica (Del.) Benth. through an allelopathic mechanism. Their root exudates contain novel flavonoid compounds, which stimulate suicidal
germination of S. hermonthica seeds and dramatically inhibit its attachment to host roots. The companion crops provide valuable forage for farm animals
while the leguminous intercrops also improve soil fertility and moisture retention. The system is appropriate as it is based
on locally available plants, not expensive external inputs, and fits well with traditional mixed cropping systems in Africa.
To date it has been adopted by more than 30 000 smallholder farmers in East Africa where maize yields have increased from
∼1 t ha−1 to 3.5 t ha−1. Future directions for semiochemical delivery by plants including biotechnological opportunities are discussed.
... Igualmente, la emisión preventiva podría generar una asociación de aprendizaje que podría conducir a que los depredadores y parasitoides logren ignorar estas claves rápidamente. Una mejor opción sería producir variedades genéticamente modificadas que respondan de una manera contundente al ataque de plagas (Whitfield, 2001). ...
Las plantas producen y emiten numerosos compuestos volátiles orgánicos. Siempre se ha reconocido el olor que producen, por su importancia comercial y estética, que liberan no sólo de flores y frutos sino también de tejidos vegetativos. Desde hace mas de dos décadas se ha establecido la influencia que ejercen los aromas sobre numerosas interacciones, en relación con funciones fisiológicas, ecológicas y más recientemente, atmosféricas. Generalmente estas mezclas están conformadas por terpenos, derivados de ácidos grasos y compuestos aromáticos. La importancia de los volátiles de plantas radica en que pueden actuar como señales para otros organismos, y aún para la misma planta; además, pueden ser exportados y modificar el entorno de las especies que los producen, sus vecinos y sus enemigos. Los volátiles químicos sirven a las plantas para: reproducción, al atraer polinizadores o dispersores de semillas; como defensa para repeler insectos o detener la colonización de bacterias y hongos fitopatógenos; para atraer enemigos naturales de herbívoros; y como mensajeros intra- e interespecíficos. Los progresos en las técnicas de análisis, la biología molecular y la bioquímica, han permitido elucidar vías biosintéticas, enzimas y genes involucrados en la producción y emisión de éstos, lo que ha ayudado a conocer parcialmente la razón del porqué se producen este tipo de sustancias, el papel que desempeñan en la interacción con otros organismos y con el medio...
... Igualmente, la emisión preventiva podría generar una asociación de aprendizaje que podría conducir a que los depredadores y parasitoides logren ignorar estas claves rápidamente. Una mejor opción sería producir variedades genéticamente modificadas que respondan de una manera contundente al ataque de plagas (Whitfield, 2001). ...
The endemic Mexican genus Pittocaulon (subtribe Tussilagininae, tribe Senecioneae, Asteraceae) belongs to a monophyletic group of genera distributed in Mexico and North America. The five Pittocaulon species represent shrubs with broom-like succulent branches. All species were found to contain pyrrolizidine alkaloids (PAs). With one exception (i.e., stems of Pittocaulon velatum are devoid of PAs) PAs were found in all plant organs with the highest levels (up to 0.3% of dry weight) in the flower heads. Three structural types of PAs were found: (1) macrocyclic otonecine esters, e.g. senkirkine and acetylpetasitenine; (2) macrocyclic retronecine esters, e.g. senecionine, only found in roots, and (3) monoesters of 1,2-saturated necines with angelic acid. For an unambiguous assignment of the different stereoisomeric 1,2-saturated necine bases a GC-MS method was established that allows the separation and identification of the four stereoisomers as their diacetyl or trimethylsilyl derivatives. All otonecine esters that generally do not form N-oxides and the 1,2-saturated PAs were exclusively found as free bases, while the 1,2-unsaturated 7-angeloylheliotridine occurring in P. velatum was found only as its N-oxide. In a comparative study the 1H and 13C NMR spectra of the four stereoisomeric necine bases were completely assigned by the use of DEPT-135, H,H-COSY, H,C-HSQC and H,H-NOESY experiments and by iterative analysis of the 1H NMR spectra. Based on these methods the PA monoesters occurring in Pittocaulon praecox and P. velatum were assigned as 7-O-angeloyl ester respectively 9-O-angeloyl ester of dihydroxyheliotridane which could be identified for the first time as naturally occurring necine base. Unexpectedly, in the monoesters isolated from the three other Pittocaulon species dihydroxyheliotridane is replaced by the necine base turneforcidine with opposite configuration at C-1 and C-7. The species-specific and organ-typical PA profiles of the five Pittocaulon species are discussed in a biogenetic context.
... Again, the relevance of these results for the resistance of plants outside the laboratory remains unknown. Clear demonstrations that HI-VOC emissions reduce the herbivore loads of plants growing in their native habitats or agricultural fields is a necessary first step if these responses are to live up to predictions that they will be agriculturally useful (Dicke et al. 1990;Whitfield 2001;Degenhardt et al. 2003;Turlings & Ton 2006). In a recent study, using maize cultivars with differential emissions of the sesquiterpene caryophyllene, Rasmann et al. (2005) demonstrated increased parasitization of corn root worm larvae on maize genotypes releasing caryophyllene, which is highly attractive to entomopathogenic nematodes. ...
The attraction of natural enemies of herbivores by volatile organic compounds as an induced indirect defence has been studied in several plant systems. The evidence for their defensive function originates mainly from laboratory studies with trained parasitoids and predators; the defensive function of these emissions for plants in natural settings has been rarely demonstrated. In native populations and laboratory Y-tube choice experiments with transgenic Nicotiana attenuata plants unable to release particular volatiles, we demonstrate that predatory bugs use terpenoids and green leaf volatiles (GLVs) to locate their prey on herbivore-attacked plants. By attracting predators with volatile signals, this native plant reduces its herbivore load - demonstrating the defensive function of herbivore-induced volatile emissions. However, plants producing GLVs are also damaged more by flea beetles. The implications of these conflicting ecological effects for the evolution of induced volatile emissions and for the development of sustainable agricultural practices are discussed.
This collection examines the many internal and external factors affecting cognitive processes. Editor Shulamith Kreitler brings together a wide range of international contributors to produce an outstanding assessment of recent research in the field. These contributions go beyond the standard approach of examining the effects of motivation and emotion to consider the contextual factors that may influence cognition. These broad and varied factors include personality, genetics, mental health, biological evolution, culture and social context. By contextualizing cognition, this volume draws out the practical applications of theoretical cognitive research while bringing separate areas of scholarship into meaningful dialogue.
The strategy of the book is to use a personal narrative to motivate chapters advancing the case for the intelligence of all living things, our kinship with, similarities to, and dependency upon other life forms, and an ethic of respect for life. It includes a critique of biocidal aspects of our culture, especially as it pertains to land use. The narrative chapters describe the process through which I became aware of the depth and pervasiveness of the environmental crisis and what I have learned through three decades of effort at ecological restoration of twenty-one acres of ruined land. The narrative chapters are used to motivate scientific descriptions of, and philosophical reflection on, various domains of life: the intelligence of insects, the analogy between soil ecosystems and the human microbiome, the inner lives of animals, and the intelligence of plants, as well as the human dependency upon healthy ecosystems—both material (through ecosystem services) and spiritual. The book calls for a radical reorientation of our attitudes and reforms in the institutions governing land use.
For more than two millennia, superior fruit tree genotypes have been grafted onto rootstocks to maintain the genetic identity of the desirable scions. Until the 20th century most fruit trees were grafted onto seedling rootstocks. Following the classification, evaluation, and propagation of clonal rootstocks during the early 1900s, dwarfing rootstocks became important to the commercial apple industries. Although trees on dwarfing rootstocks are more economical to maintain, and are more precocious and productive than trees on seedling rootstocks, there remains a need for dwarfing rootstocks to be adapted to different growing conditions. During the past 100 years, considerable effort has been made to understand the physiological changes in the scion induced by rootstocks. More recently, molecular techniques have been utilized to identify the genes that control interactions between scion and rootstock. Modern rootstock breeding programs are combining molecular and traditional techniques to develop rootstocks that are dwarfing, productive, and tolerant to biotic and abiotic stresses. In this chapter, the history, development and current use of apple rootstocks, the current understanding of rootstock–scion interactions, and current efforts to develop and evaluate superior rootstocks are discussed.
This collection examines the many internal and external factors affecting cognitive processes. Editor Shulamith Kreitler brings together a wide range of international contributors to produce an outstanding assessment of recent research in the field. These contributions go beyond the standard approach of examining the effects of motivation and emotion to consider the contextual factors that may influence cognition. These broad and varied factors include personality, genetics, mental health, biological evolution, culture and social context. By contextualizing cognition, this volume draws out the practical applications of theoretical cognitive research while bringing separate areas of scholarship into meaningful dialogue.
Thrips palmi is a major pest of many crops in the tropics and sub-tropics, and is a serious threat within the protected horticulture industry in other parts of the world including the UK. Widespread use of insecticides against T. palmi throughout the world coupled with the restricted range of products available makes it essential to find alternative systems for control. The scattered information on its natural enemies, particularly predators and parasitoids, is reviewed and their potential for use in the control of T. palmi as part of IPM strategies in the UK is considered. Natural enemies selected for detailed examination include: Amblyseius spp., Anthocoris nemoralis, Atheta coriaria, Bilia spp., Campylomma spp., Ceranisus spp., Deraeocoris spp., Franklinothrips spp., Hypoaspis spp., Orius spp. and Phytoseius spp. Recommendations for further investigations are made, including screening and efficacy testing of candidate predators and parasitoids, using semiochemicals to enhance their effectiveness, and assessing the compatibility of chosen species with other components of an IPM system.
Without Abstract Leaves normally release low levels of volatile chemicals. However, when a plant is
Cotton is infested by sucking pests (aphids, jassids, whiteflies, thrips, plant bugs) and bollworms causing deterioration in lint quality and 10-40% losses in crop production. Insecticides used extensively to control these pests cause undesirable secondary effects including the destruction of arthropod parasitoids, which constitute an important component of pest management. When released parasitoids die or become ineffective in cotton ecosystems, the classical biological control fails. Therefore, conservation of potential parasitoids is nowadays considered a major step in maintaining populations in a region where they could reduce the pest population density below economic thresholds and reduce plant damage below economic injury levels. By employing the least disruptive control measures and by adopting proper habitat management, it would be possible to enhance the survival, conservation and physiological/behavioural performance of the generalist and specific parasitoids in cotton-production systems.
Plants can respond to damage by pests with both induced direct defences and indirect defences by the attraction of their natural enemies. Foliar application of several plant-derived chemicals, such as salicylic acid and oxalic acid, can induce these defence mechanisms. The effect of acetylsalicylic acid and oxalic acid on the aphid Myzus persicae Sulzer (Homoptera: Aphididae) and its parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae) was investigated. Experiments were carried out with direct application of acetylsalicylic and oxalic acids on these insects, as well as choice and no-choice tests using foliar application of both chemicals on Brussels sprouts plants, Brassica oleracea var. gemmifera L. (Brassicaceae). Parasitoids were given a choice between treated and untreated plants for oviposition, and the effects of the chemicals on aphid and parasitoid development were determined. Although direct application of both chemicals increased aphid mortality, their foliar application did not induce resistance against aphids. The foliar application of such compounds, even in low concentration as shown in the choice tests, has the potential to induce indirect plant defences against aphids by encouraging aphid parasitisation. Although the direct application of both chemicals reduced parasitoid emergence from their hosts, the foliar application of acetylsalicylic acid and low concentrations of oxalic acid did not have a negative effect on parasitoid emergence ability. However, 10 mm oxalic acid reduced the number of emerged parasitoids in no-choice experiments. This study shows that foliar application of acetylsalicylic and oxalic acids has the potential to encourage aphid parasitisation, but care is needed as high concentrations of oxalic acid can have a negative effect on these beneficial organisms.
Plants respond to chemical signals (semiochemicals) that are associated with insect or pathogen attack by modifying their
metabolism accordingly so that defence pathways are switched on or primed. Once the relevant semiochemicals or analogues are
identified, these signals can be artificially applied to achieve similar effects. Such plant activator agrochemicals represent
an entirely different approach from the one traditionally used by the agrochemical industry of deploying pesticide molecules
to kill pests. These chemicals do not have direct effects on pests and diseases but upregulate plant defence genes that increase
plant resistance to attack. Plant activators are compatible with integrated pest management (IPM) systems and even enhance
biocontrol techniques by promoting plant attractiveness to natural enemies of plant pests, as natural enemies of pests prefer
induced plants. The plant defence traits activated are often complex relying on the expression of many genes, which makes
it harder for pests to adapt to them. Current practise and future prospects are reviewed in this chapter.
Crop yields are reduced and destabilized by pests which also affect the quality of harvested produce. To keep pace with growing
demand, global food production needs to increase by an estimated 70% by 2050. Thus, the losses caused by pests need to be
tackled. Synthetic pesticides have provided cost-effective control of pests over the last few decades but have several disadvantages.
They may adversely affect natural enemies of insect pests, which would otherwise provide a degree of control and pests may
evolve resistance to the pesticide. The discovery rate of novel bioactive compounds is low and their exploitation increasingly
inhibited by stringent regulatory requirements. Use of resistant crop cultivars is another solution but when based on single
genes it also suffers from the evolution of biotypes of pests that can overcome the resistance conferred by the gene. Biocontrol
with natural enemies can contribute to pest management but biocontrol agents are often hard to maintain at sufficiently high
levels in open field environments. New solutions could include novel resistant cultivars with multiple resistance genes, suitable
epigenetic imprints and improved defence responses that are induced by attack. Plant activator agrochemicals could be used
to switch on natural plant defence. Habitat manipulations such as push-pull can improve pest management and yields in less
intensive systems. Genomic and transcriptomic information will facilitate development of new resistant crop cultivars once
annotation and availability of data on multiple cultivars is improved. Knowledge of the chemical ecology of pest-plant interactions
will be better exploited once the genes for biosynthesis of key plant metabolites are discovered. Genetic modification of
crops has the potential for speeding the development of crops with novel resistance.
KeywordsCrop pest–Food security–Induced defence–IPM–Resistant cultivar
It is of adaptive value for a plant to prepare its defenses when a threat is detected, and certain plant volatiles associated with insect damage, such as cis-jasmone (CJ), are known to switch-on defense metabolism. We used aphid and aphid parasitoid responses to Arabidopsis thaliana as a model system for studying gene expression and defense chemistry and its impact at different trophic levels. Differential responses to volatiles of induced Arabidopsis occurred for specialist and generalist insects: the generalist aphid, Myzus persicae, was repelled, whereas the specialist, Lipaphis erysimi, was attracted; the generalist aphid parasitoid Aphidius ervi was attracted, but the specialist parasitoid Diaeretiella rapae was not affected. A. ervi also spent longer foraging on induced plants than on untreated ones. Transcriptomic analyses of CJ-induced Arabidopsis plants revealed that a limited number of genes, including a gene for a cytochrome P450, CYP81D11, were strongly up-regulated in the treated plants. We examined transgenic Arabidopsis lines constitutively overexpressing this gene in bioassays and found insect responses similar to those obtained for wild-type plants induced with CJ, indicating the importance of this gene in the CJ-activated defense response. Genes involved in glucosinolate biosynthesis and catabolism are unaffected by CJ and, because these genes relate to interactions with herbivores and parasitoids specific to this family of plants (Brassicaceae), this finding may explain the differences in behavioral response of specialist and generalist insects.
• induced defense
• plant volatile
• plant–insect interaction
• stress response
Wounding increases the levels and activities of several defense-related proteins in the foliage of the tomato plant,Lycopersicon esculentum Mill. Evidence indicates that two of these responses, the systemic increases in polyphenol oxidase and proteinase inhibitors, are regulated by an octadecanoid-based signalling pathway which includes the wound hormone, jasmonic acid. It is not known whether other responses to wounding are also regulated by this same signalling pathway. In this paper, we show that application of jasmonates (jasmonic acid or its volatile derivative, methyl jasmonate) in low concentrations to foliage of young tomato plants induced, in a dose-dependent manner, the same protein responses-polyphenol oxidase, proteinase inhibitors, lipoxygenase, and peroxidase-as doesHelicoverpa zea Boddie feeding. Application of jasmonic acid to a single leaflet of four-leaf tomato plants induced these four proteins in a spatial pattern nearly identical to that produced by localized feeding ofH. zea. Exogenous jasmonic acid also decreased suitability of foliage for the beet armyworm,Spodoptera exigua Hubner in the laboratory. Based on these results, we conducted an experiment to measure the effects of jasmonic acid spray under field conditions. We provide the first evidence that jasmonic acid spray on field plants induces production of chemical defenses above the levels found in unsprayed controls. Exogenous jasmonic acid sprayed on plants in agricultural plots increased levels of polyphenol oxidase and proteinase inhibitors. Because application of jasmonic acid induces these defensive compounds at low concentrations in a manner similar to natural wounding, it may prove to be a useful tool for stimulating plant resistance to insects in the field.
Maize ( Zea mays L.) releases specific volatiles in response to herbivory by caterpillars. These volatiles are known to serve as cues for parasitic wasps to locate the herbivores. In the present study the exact time of volatile emission after simulated herbivory (mechanical damage and treatment with caterpillar regurgitant) was measured for seedlings of the cultivars "Ioana Sweet Corn" and "LG11". Odours were collected every 0.5 h for a total of 12 h. Typical "green leaf odours", (Z)-3-hexenal, ( E )-2-hexenal, (Z)-hexen-1-o1, and (Z)-3-hexen-1-yl acetate, were emitted immediately upon damage and their amounts dropped rapidly after the first collections. Several of the induced compounds were released within 2 h after treatment, while others (mainly sesquiterpenoids) started to be released after 4 h. The LG11 seedlings emitted several compounds (e.g. β-myrcene, (Z)-β-ocimene, benzyl acetate, β-caryophyllene, ( E,E )-α-farnesene) that were not detected for Ioana. ( E,E )-α-farnesene was continuously emitted by LG11 seedlings, even by undamaged plants. Timing of the release of volatile compounds that the two varieties had in common did not differ significantly, with the exception of indole for which the peak production was considerably earlier for LG11. These findings are discussed in the context of biosynthetic pathways and mechanisms involved in induced emissions of plant volatiles and the exploitation of the resulting odour by parasitoids and predators of herbivores.
Parasitic and predatory arthropods often prevent plants from being severely damaged by killing herbivores as they feed on the plants. Recent studies show that a variety of plants, when injured by herbivores, emit chemical signals that guide natural enemies to the herbivores. It is unlikely that herbivore-damaged plants initiate the production of chemicals solely to attract parasitoids and predators. The signaling role probably evolved secondarily from plant responses that produce toxins and deterrents against herbivores and antibiotics against pathogens. To effectively function as signals for natural enemies, the emitted volatiles should be clearly distinguishable from background odors, specific for prey or host species that feed on the plant, and emitted at times when the natural enemies forage. Our studies on the phenomena of herbivore-induced emissions of volatiles in corn and cotton plants and studies conducted by others indicate that (i) the clarity of the volatile signals is high, as they are unique for herbivore damage, produced in relatively large amounts, and easily distinguishable from background odors; (ii) specificity is limited when different herbivores feed on the same plant species but high as far as odors emitted by different plant species and genotypes are concerned; (iii) the signals are timed so that they are mainly released during the daytime, when natural enemies tend to forage, and they wane slowly after herbivory stops.
Herbivore attack is known to increase the emission of volatiles, which attract predators to herbivore-damaged plants in the
laboratory and agricultural systems. We quantified volatile emissions fromNicotiana attenuata plants growing in natural populations during attack by three species of leaf-feeding herbivores and mimicked the release
of five commonly emitted volatiles individually. Three compounds (cis-3-hexen-1-ol, linalool, and cis-α-bergamotene) increased egg predation rates by a generalist predator; linalool and the complete blend decreased lepidopteran
oviposition rates. As a consequence, a plant could reduce the number of herbivores by more than 90% by releasing volatiles.
These results confirm that indirect defenses can operate in nature.
Many plant species respond to herbivory with de novo production of a mixture of volatiles that attracts carnivorous enemies of the herbivores. One of the major components in the blend of volatiles produced by many different plant species in response to herbivory by insects and spider mites is the homoterpene 4,8-dimethyl-1,3(E),7-nonatriene. One study (J. Donath, W. Boland [1995] Phytochemistry 39: 785–790) demonstrated that a number of plant species can convert the acyclic sesquiterpene alcohol (3S)-(E)-nerolidol to this homoterpene. Cucumber (Cucumis sativus L.) and lima bean (Phaseolus lunatus L.) both produce 4,8-dimethyl-1,3(E),7-nonatriene in response to herbivory. We report the presence in cucumber and lima bean of a sesquiterpene synthase catalyzing the formation of (3S)-(E)-nerolidol from farnesyl diphosphate. The enzyme is inactive in uninfested cucumber leaves, slightly active in uninfested lima bean leaves, and strongly induced by feeding of the two-spotted spider mite (Tetranychus urticae Koch) on both plant species, but not by mechanical wounding. The activities of the (3S)-(E)-nerolidol synthase correlated well with the levels of release of 4,8-dimethyl-1,3(E),7-nonatriene from the leaves of the different treatments. Thus, (3S)-(E)-nerolidol synthase is a good candidate for a regulatory role in the release of the important signaling molecule 4,8-dimethyl-1,3(E),7-nonatriene.
Volatile compounds elicited by insect herbivore feeding damage in five cotton cultivars and one naturalized cotton variety were examined by allowing beet armyworm larvae to feed overnight on leaves and collecting volatiles from the plants in situ. Of 23 compounds identified from larval damaged leaves, terpenes and lipoxygenase-hydroperoxide lyase-derived volatiles predominated. No pronounced differences in the levels of volatile emission were noted from leaves of undamaged plants of the different varieties. However, average volatile emission from damaged leaves of the naturalized variety was almost sevenfold higher than from damaged leaves of the commercial cultivars. This was despite the fact that larvae preferred feeding on the leaves of commercial cultivars over those of the naturalized variety in choice tests.
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.
Plants and carnivorous arthropods can interact mutualistically. A recent discovery is that such mutualisms can be mediated by volatile compounds — produced by plants in response to herbivore damage — that attract carnivores. However, after emission of these attractants, the plant has no control over their use. Thus, exploitation of the information may occur, to the detriment of the plant, leading to costs in addition to benefits. Although all plants studied to date become attractive to carnivorous arthropods after damage by herbivores, they do so in different ways and it is important to understand why this is so.
Phytophagous mites are a serious threat to their host plants; in absence of predators they tend to overexploit their food source. To prevent such a crash and maintain as much leaf area as possible host plants may defend themselves in various ways, one of which is to increase the effectiveness of natural enemies of the phytophagous mites. Predatory mites are considered to be very important natural enemies of plant-feeding mites and there is evidence for a mutualistic interaction with plants. Examples of how plants obtain and arrest predatory mites as bodyguards are discussed. It is known for a long time that some plant species provide pollen that appear to be a very profitable food source for some species of predatory mites: it does not only promote survival, but also allows development and egg production. In doing so, plants ensure themselves of bodyguards even before any damage is inflicted. Recently, evidence has been obtained that plants under attack by spider mites provide information by releasing a blend of volatile chemicals that are helpful to predatory mites in locating their prey. Plant-predator interactions are not always of a mutualistic nature. Some plant species invest in a rigorous defence against spider mites, even though this may be to the detriment of the predators: glandular hairs of some plant species entrap not only spider mites, but also their predators. The evolutionary implications of these various plant-predator interactions are discussed.
As part of a programme for controlling lepidopteran stem-borers in cereal crops in Africa, we have investigated the effectiveness of combined cropping regimes of cultivatedand wild plants for reducing stem-borer damage. Intercropping with the non-host molasses grass, Melinis minutiflora, significantly decreased levels of infestation by stem-borers in the main crop and also increased larval parasitism of stem-borers by Cotesia sesamiae. Volatile agents produced by M. minutiflora repelled female stem-borers and attracted foraging female C. sesamiae. One of the volatile components released by intact M. minutiflora which attract parasitoids is also produced by herbivore-damaged plants and is implicated more widely as a cue for stimulating predation and parasitism.
Upon herbivore attack, maize (Zea mays L.) emits a mixture of volatile compounds that attracts herbivore enemies to the plant. One of the major components of this mixture is an unusual acyclic C11 homoterpene, (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), which is also emitted by many other species following herbivore damage. Biosynthesis of DMNT has been previously shown to proceed via the sesquiterpene alcohol, (E)-nerolidol. Here we demonstrate an enzyme activity that converts farnesyl diphosphate, the universal precursor of sesquiterpenes, to (3S)-(E)-nerolidol in cell-free extracts of maize leaves that had been fed upon by Spodoptera littoralis. The properties of this (E)-nerolidol synthase resemble those of other terpene synthases. Evidence for its participation in DMNT biosynthesis includes the direct incorporation of deuterium-labeled (E)-nerolidol into DMNT and the close correlation between increases in (E)-nerolidol synthase activity and DMNT emission after herbivore damage. Since farnesyl diphosphate has many other metabolic fates, (E)-nerolidol synthase may represent the first committed step of DMNT biosynthesis in maize. However, the formation of this unusual acyclic terpenoid appears to be regulated at both the level of (E)-nerolidol synthase and at later steps in the pathway.