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Herbivory-induced stress: Leaf developmental instability is causeby herbivore damage in early stages of leadevelopment.
... This biomonitoring tool estimates the inability of an organism to undergo stable development under certain environmental/ biotic conditions (Møller 1998;Komac and Alados 2012;Ivanov et al. 2015). As a rule, stressful conditions, including herbivory and gall attack, are positively related to FA (Zvereva et al. 1997;Santos et al. 2013;Alves-Silva and Del-Claro 2016). Other instances, including pollution, poor microhabitat conditions, low soil nutrition and competition, are related to high levels of FA (reviewed in Møller and Shykoff 1999;Graham et al. 2010;Beasley et al. 2013). ...
... Fluctuating asymmetry has long been used as a measure of population stress, and several environmental factors are recognised to increase FA in plants (Raz et al. 2011), but the role of biotic factors (e.g. herbivory) as a cause of FA has been poorly explored (Zvereva et al. 1997;Alves-Silva and Del-Claro 2016). In the B. brevipes-S. ...
The hypersensitive response is an important form of plant-induced defence against galling insects and can imply changes in leaf nutrients, especially nitrogen and carbon, which are important for both gall survivorship and leaf development. We hypothesised that the hypersensitive response also causes leaf stress, which can be measured using leaf fluctuating asymmetry. This method evaluates deviations from leaf symmetry and is used to assess the health of plant populations, given that stressful conditions are positively related to levels of fluctuating asymmetry. In the current study, we investigated whether the hypersensitive response of Bauhinia brevipes (Fabaceae) to gall induction by Schizomyia macrocapillata (Cecidomyiidae) was related to differences in leaf nutrients (nitrogen and organic carbon) and/or levels of fluctuating asymmetry. More than 85 % of gall midges perished due to hypersensitive reactions. Fluctuating asymmetry was positively related to the hypersensitive response, and, consequently, this provides evidence that an induced response against herbivores increases plant stress. The concentration of nitrogen was negatively related to the hypersensitive response, indicating that leaves with increased induced defence tend to have low nitrogen levels, which could affect gall development and survival. Organic carbon was related neither to the hypersensitive response nor to fluctuating asymmetry. Galls are known to affect negatively plant development, and here we show that an induced defence against galls is related to differences in plant nitrogen and developmental stability.
... Experiment 3: To test tolerance, we used different intensities of simulated herbivory to assess the impacts on leaf asymmetry. This metric is commonly used as a biomarker of stress [51,52]. We did not evaluate reproductive components, because plants were still saplings and then did not flower. ...
Plants express many types of defenses in response to herbivory damage. These defenses can be displayed as a sequence or they can overlap, increasing efficiency in protection. However, leaf defense shifts during leaf development, including extrafloral nectaries (EFNs), are neglected in natural tropical systems. To address this gap, our study evaluates the shifts in defense strategies of Eriotheca gracilipes, focusing on extrafloral nectaries and leaf toughness across leaf development stages. We also simulate herbivory by cutting the leaves to address the role of visiting ants against herbivores. We observed that E. gracilipes exhibits a defense turnover, shifting from indirect defenses (e.g., EFNs) in young leaves to physical defenses in adult leaves. Simulated herbivory led to heightened ant visitation, which correlated with decreased herbivory rates, indicating that ant recruitment acts as an effective deterrent. We observed a peak of EFN activity in young leaves, increased foliar toughness in adult leaves, and reduced herbivory on ant-patrolled young leaves. Additionally, E. gracilipes demonstrated tolerance to up to 10% foliar loss with no significant impact on leaf asymmetry, although 50% foliar loss increased asymmetry in newly flushed leaves. These results highlight E. gracilipes’ adaptive flexibility by attracting protective ants when vulnerable and enhancing structural defenses as leaves develops, E. gracilipes minimizes herbivory impact. This study provides valuable insight into the adaptive roles of EFNs and tolerance in E. gracilipes, contributing to a broader understanding of plant defense strategies.
... KEYWORDS aristolochic acids, C/N ratio, plant age, plant-herbivore interaction, seasonal variation, plant defense Introduction Plants are continuously exposed to a variety of biotic and abiotic stresses in their natural environment. Herbivory is a major cause of biotic stress for plants (Mattson, 1980;Karban and Myers, 1989;Alves-Silva and Del-Claro, 2016;Iqbal et al., 2021). Plants are dynamic organisms that can optimize cost-benefit balance between growth and defense to deal with the herbivory stress (Herms and Mattson, 1992). ...
Plants need to balance investments in growth and defense throughout their life to increase their fitness. To optimize fitness, levels of defense against herbivores in perennial plants may vary according to plant age and season. However, secondary plant metabolites often have a detrimental effect on generalist herbivores, while many specialists have developed resistance to them. Therefore, varying levels of defensive secondary metabolites depending on plant age and season may have different effects on the performance of specialist and generalist herbivores colonizing the same host plants. In this study, we analyzed concentrations of defensive secondary metabolites (aristolochic acids) and the nutritional value (C/N ratios) of 1st-, 2nd- and 3rd-year Aristolochia contorta in July (the middle of growing season) and September (the end of growing season). We further assessed their effects on the performances of the specialist herbivore Sericinus montela (Lepidoptera: Papilionidae) and the generalist herbivore Spodoptera exigua (Lepidoptera: Noctuidae). Leaves of 1st-year A. contorta contained significantly higher concentrations of aristolochic acids than those of older plants, with concentrations tending to decrease over the first-year season. Therefore, when first year leaves were fed in July, all larvae of S. exigua died and S. montela showed the lowest growth rate compared to older leaves fed in July. However, the nutritional quality of A. contorta leaves was lower in September than July irrespective of plant age, which was reflected in lower larval performance of both herbivores in September. These results suggest that A. contorta invests in the chemical defenses of leaves especially at a young age, while the low nutritional value of leaves seems to limit the performance of leaf-chewing herbivores at the end of the season, regardless of plant age.
... Another morphological method of evaluating the environmental impact is the assessment of the instability of development. Such instability mostly assessed by the index of fluctuating asymmetry during the response of plant populations to biotic stressors, such as damage by herbivores (insects, crabs, birds), intraspecies competition (Komac and Alados, 2012;Alves-Silva and Del-Claro, 2016;Maldonado-López et al., 2019), and other environmental stress factors, such as shading, urbanization (Wuytack et al., 2011;Cuevas-Reyes et al., 2013). A significant increase in the FA index of clover leaves collected at a site near the storage of radioisotope thermoelectric generators was found in the work (Gorshkovа et al., 2014), where the dose rate was 50-60 times higher than the natural background radiation. ...
A comprehensive study of the biological effects of chronic radiation exposure (8 μGy/h) in populations of white clover (Trifolium repens L.) from the Chernobyl exclusion zone was carried out. White clover is one of the most important pasture legumes, having many agricultural applications. Studies at two reference and three radioactively contaminated plots showed no stable morphological effects in white clover at this level of radiation exposure. Increased activities of catalase and peroxidases were found in some impacted plots. Auxin concentration was enhanced in the radioactively contaminated plots. Genes involved in the maintenance of water homeostasis and photosynthetic processes (TIP1 and CAB1) were upregulated at radioactively contaminated plots.
... Differences in nutritional quality and chemical defenses of plants have been suggested to explain these contrasting results (Cornelissen and Stiling 2011). On the other hand, plants can be directly stressed by herbivorous insects producing changes in leaf symmetry and increasing FA levels (herbivory-induced stress hypothesis) (Alves- Silva and Del-Claro 2016). In this way, FA in plants can increase as a result of herbivory intensity (Cuevas-Reyes et al. 2011b). ...
Key message
This paper shows the intraspecific plant responses in leaf morphology, herbivory and FA between mature and successional tropical dry forests, as well as the difficulty associated with understanding the relationship between FA and herbivory
Abstract
Understanding the processes that affect biotic interactions during secondary succession has implications for the maintenance of species diversity in the tropics. We studied the changes in leaf morphology, fluctuating asymmetry (FA) and herbivory in three dominant tropical dry forest plant species that occur in mature and secondary forests. We selected eight study sites: four in mature and four in successional forests. At each site, a plot of 20 × 50 m was established to characterize the vegetation structure and soil fertility. Subsequently, leaf morphology, FA and herbivory were measured in all individuals of Cordia elaeagnoides, C. alliodora and Achatocarpus gracilis with DBH ≥ 2.5 cm found in the plots. Plant abundance and plant height decreased in secondary forest, while the content of nitrates and phosphates increased in soil of secondary forests. Differences in leaf morphology between forest conditions were found for the three species. Total leaf area was higher in mature than in secondary forests for C. elaeagnoides and A. gracilis. An opposite pattern was found for C. alliodora. In both Cordia species, herbivory was higher in secondary than in mature forests. The opposite pattern was found for A. gracilis in secondary forests. For all the cases, FA was higher in mature forests than in secondary forests. Herbivory was positively correlated with FA in secondary forests in C. elaeganoides and in A. gracilis, whereas in C. alliodora herbivory was positively related with FA in mature forests. Overall, we detected changes in foliar morphology, fluctuating asymmetry and herbivory between mature and secondary forests, with a general pattern of higher FA levels in mature forests. Our findings illustrate the difficulty associated with understanding the relationship between FA and herbivory throughout the regeneration process in tropical dry forests due to the complexity of abiotic and biotic factors that can affect plant–herbivore interactions.
... A mechanistic explanation for the detected pattern is lacking at the moment, because of the acute shortage of information on factors that affect the FA and photosynthetic efficiency of individual leaves. The within-plant variation in FA can be associated with many factors, including the ontogeny of the individual modules, the temporal and spatial micro-environmental variation and the current and previous-year damage by herbivores [22,33,[51][52][53]. However, in our study, the geographic or climatic differences and ontogenetic changes in leaf size and SLA were not responsible for the positive relationship between FA and F v /F m , because this relationship was not removed when the two traits were included as covariates. ...
Symmetry pervades nature, but asymmetry is also rather common. Deviations from genetically programmed symmetry are usually associated with internal or external developmental disturbances and may therefore be related to imperfections in physiological processes. In this study, we test the hypotheses that the photosynthetic efficiency of individual leaves of a plant is negatively related to their asymmetry. We measured chlorophyll fluorescence in leaves of three woody species (Betula pubescens, Populus tremula and Salix caprea) in early and late summer in two localities situated ca. 1000 km apart, and we quantified the asymmetry of these leaves by a multivariate measure based on the relative positions of several landmarks. Contrary to our expectation, we found that the photochemical efficiency of photosystem II was positively correlated with leaf fluctuating asymmetry; this effect was weak but consistent across the studied plant species, localities and seasons. Our finding adds to limited evidence that within-plant variation in leaf asymmetry is associated with variation in leaf physiology. Irrespective of the underlying mechanisms, which remain unknown, the results suggest that trees may benefit even more from their asymmetric leaves, at least in terms of photosynthesis, than they do from their more symmetric leaves.
... The relation between herbivory and developmental stability is an important issue, and FA can be used to analyze it. FA is often considered to be an indicator of stress (since stressed plants tend to attract herbivores) or can represent the consequence of herbivory (when herbivores induce asymmetry) (Alves- Silva and Del-Claro 2016). Higher FA values could indicate higher leaf-nutritive value and lower levels of chemical defense (Lempa et al. 2000) so herbivores may use departures from perfect symmetry as a sign that a plant represents better quality food (Cornelissen and Stiling 2005a). ...
Light environments can influence variation in plant morphology, development and susceptibility to herbivores. Our research interest was to investigate the patterns of herbivore damage and developmental stability in dioecious understory forb Mercurialis perennis in contrasting light habitats, located at 1700 m a.s.l. on Mt. Kopaonik. Male and female plants from two light habitats, open (a sun-exposed field) and shaded (a spruce forest) were examined with respect to: herbivore damage (percentage of leaf area loss), fluctuating asymetry (FA) as a measurement of developmental stability, plant morphological and, specifically, leaf size traits, as well as biochemical traits relating to nutritional quality and defence, taking into account the possible presence of intersexual differences. Our results show that herbivore damage was significantly higher in open habitat, as well as one out of four univariate FA indices and the multivariate index. Morphological and biochemical traits, apart from defensive compounds, had higher values in the shade, pointing to sun-exposed habitat being more stressful for this species. Intersexual differences were observed for foliar damage, defensive compounds (phenolics and tannins), all leaf size traits, total leaf area, and protein content. Contrasting light habitats affected most of the analysed traits. Both foliar damage and FA were higher in a more stressful habitat; within habitats, no positive correlations were found. Herbivore damage was significantly male biased in open habitat. The analysis of intersexual differences in developmental stability measured by leaf asymmetry levels provided no evidence that female plants were more sensitive to environmental stress.
... In the past ten years or so there has been a renewed interest in developmental instability and the response of populations to several alleged stressors, namely biotic stressors (e.g. herbivory, parasitism and competition, see Cuevas-Reyes et al., 2013;Komac and Alados, 2012;Santos et al., 2013;Alves-Silva and Del-Claro, 2016a) and environmental stressors (e.g. pollutants, sun-shade, see Raz et al., 2011;Wuytack et al., 2011). ...
One issue in studies of leaf asymmetry is the lack of standardization of sample sizes for estimating the different types of leaf asymmetry, namely fluctuating asymmetry (FA -, differences in leaf sides around zero, normally distributed data), directional asymmetry (DA - one leaf side is substantially larger than the other) and antisymmetry (AS - both right-and left-sidedness; bimodal data). FA is the only parameter regarded as a biomarker of stress and it is used consistently for population monitoring. Here we investigated whether leaf samples of different sizes showed different asymmetries (FA, DA or AS) in three unrelated plant species (Miconia fallax, Solanum lycocarpum and Bauhinia brevipes). We hypothesized that larger samples would show FA, as substantial side differences would be buffered and so that the sample would display differences in leaf sides around zero (i.e., FA). The results were highly dependent on both sample size and plant species. Larger samples did not consistently display FA, but they did provide leaf asymmetry values close to zero, which is a prerequisite of FA. AS was pervasive, but detailed exploration of histograms revealed that none of the data sets had a bimodal distribution and most curves were leptokurtic. On this basis, we suggest that kurtosis tests in combination with histograms should be given preference over normality tests as a method to evaluate potential AS. We conclude that at this time it is still not possible to give a rule-of-thumb for sample sizes for this type of investigation, and that graphical representations of data should be used to classify the asymmetry types more accurately. We suggest that the statistical tests used to examine FA should be reconsidered and that graphs such as histograms can be more informative than p-values when it comes to distinguishing between types of leaf asymmetry.
Many dicotyledonous plants employ folding of immature leaf surfaces into buds before developing into mature leaves. Bud folding in leaves is impacted by taxonomy and ecology, and fossil evidence provides insight into its evolution. Direct evidence of leaf-bud folding patterns is rare in the fossil record. Herein, we describe leaf compressions from the middle Eocene (47.8–37.71 Ma) Geiseltal lignite deposits in Germany, which exhibit feeding damage consisting of files of holes across the leaf (damage types DT06 and DT425). We compare the damage on these leaves to various models of bud-feeding, including digital and paper origami, and artificial damage to living leaf buds, to more accurately interpret the fossils. One of the specimens exhibits a complex damage pattern, which can be roughly assigned to seven lines of holes across the leaf. Models based on this fossil leaf indicate that the pattern of damage is consistent with an insect feeding on a leaf bud that was folded in a semi-corrugated pattern, creating the observed damage after bud burst (DT06). The two other fossil leaves exhibit a simpler pattern of bilaterally symmetrical damage. This likely resulted from an insect feeding on these leaves while they were folded in half, as a bilaterally folded bud, or a mature leaf folded in half at night or in response to herbivory (DT425). The patterns observed in these fossil leaves may confirm ecologies and life histories that are not otherwise directly recorded. Moreover, the models presented here contribute to recognizing bud-feeding traces in the fossil record.
Plant responses to damage by insectivorous herbivores are well-documented in mature leaves. The resulting herbivore-induced plant volatiles (HIPVs) protect the plant by attracting carnivorous arthropods and even some insectivorous vertebrates, to parasitize or consume the plant invaders. However, very little is known about plant production of HIPVs in developing buds, particularly when herbivorous insects are too small to be considered a prey item. It is additionally unclear whether plants respond differently to generalist and specialist chewing insects that overlap in distribution. Therefore, we compared HIPV production of Downy oak (Quercus pubescens Willd.) buds infested with freshly hatched caterpillars of Tortrix viridana (specialist) and Operophtera brumata (generalist), against uninfested buds. Of the compounds identified in both years of the experiment, we found that (Z)-hex-3-enyl acetate, (E)-β-ocimene, acetophenone, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate, α-copaene, α-humulene, (E)-caryophyllene, and (E,E)-α-farnesene appeared to be higher in infested buds compared to controls. We found no difference in HIPV production between the specialist and the generalist herbivores. Production of HIPVs was also associated with leaf damage, with higher HIPV production in more severely attacked buds. Thus, our study shows that oak trees already start responding to insect herbivory before leaves are developed, by producing compounds similar to those found in damaged mature leaves. Future work should focus on how Downy oak may benefit from initiating alarm cues at a time when carnivorous arthropods and insectivorous vertebrates are unable to use herbivorous insects as host or food.
Thrips are serious pests of Hemerocallis citrina Baroni (daylily), affecting crop yield and quality. To defend against pests, daylily has evolved a set of sophisticated defense mechanisms. In the present study, induction of systemic resistance in Hemerocallis citrina ‘Datong Huanghua’ by Thrips palmi feeding was investigated at both biochemical and molecular levels. The soluble sugar content of daylily leaves was significantly lower than that in control check (CK) at all time points of feeding by T. palmi, whereas the amino acid and free fatty acid contents started to be significantly lower than those in CK after 7 days. Secondary metabolites such as tannins, flavonoids, and total phenols, which are harmful to the growth and reproduction of T. palmi, were increased significantly. The activities of defense enzymes such as peroxidase (POD), phenylalanine ammonia lyase (PAL), and polyphenol oxidase (PPO) were significantly increased, and the degree of damage to plants was reduced. The significant increase in protease inhibitor (PI) activity may lead to disrupted digestion and slower growth in T. palmi. Using RNA sequencing, 1,894 differentially expressed genes (DEGs) were identified between control and treatment groups at five timepoints. DEGs were mainly enriched in secondary metabolite synthesis, jasmonic acid (JA), salicylic acid (SA), and other defense hormone signal transduction pathways, defense enzyme synthesis, MAPK signaling, cell wall thickening, carbohydrate metabolism, photosynthesis, and other insect resistance pathways. Subsequently, 698 DEGs were predicted to be transcription factors, including bHLH and WRKY members related to biotic stress. WGCNA identified 18 hub genes in four key modules (Purple, Midnight blue, Blue, and Red) including MYB-like DNA-binding domain (TRINITY_DN2391_c0_g1, TRINITY_DN3285_c0_g1), zinc-finger of the FCS-type, C2-C2 (TRINITY_DN21050_c0_g2), and NPR1 (TRINITY_DN13045_c0_g1, TRINITY_DN855_c0_g2). The results indicate that biosynthesis of secondary metabolites, phenylalanine metabolism, PIs, and defense hormones pathways are involved in the induced resistance to T. palmi in daylily.
Associational resistance (AR) is a positive interaction in which a plant suffers less damage caused by herbivores due to its association with a protective plant. Here, we evaluated whether plants with extrafloral nectaries (EFNs) can share indirect defenses with neighboring plants. We sampled 45 individuals of an EFN-bearing liana (Smilax polyantha) and recorded whether their support species had EFNs. In S. polyantha, we measured foliar herbivory and flower and fruit production. We examined the ant species composition and visitation of S. polyantha and whether they changed according to the supporting plant type (with or without EFNs). We experimentally determined whether S. polyantha supplemented with artificial nectaries could share indirect defenses with defenseless neighboring plants. Support plants with EFNs indirectly benefited S. polyantha by sharing mutualistic ant species. Smilax polyantha supported by plants with EFNs had a more specific ant species composition, a higher number of visiting ants and ant species richness, and nearly 3 times less foliar herbivory. However, we did not observe differences in fruit production between the two groups of S. polyantha. Finally, we observed that S. polyantha with artificial nectaries increased ant visitation on neighboring plants 2.5 times. We provide evidence that interspecific neighbors with EFNs can experience reciprocal benefits by sharing indirect defenses. Such local effects might escalate and affect the structure of plant communities.
CONTEXT
Temperate forest ecosystems harbor great biodiversity and provide key ecosystem services. However, in Mexico they have been deforested for use in avocado orchards, which represents a major threat to ecosystems functioning and the conservation of biodiversity.
OBJECTIVE
We evaluated the changes in soil chemical properties in a fragmented landscape of avocado agrosystems and forests in Mexico and the effects on plant quantity and quality (leaf area, canopy cover, DBH and chlorophyll content), leaf morphology, herbivory and fluctuating asymmetry in Quercus castanea and Q. obtusata.
METHODS
Eight study sites were selected: i) areas with a more proportion of forest and less of avocado orchards, ii) areas with equal proportion of both forest and orchards, iii) areas with more proportion of orchards. In all sites, 15 adult trees at the edge and 15 trees in the interior of each fragment were selected for each oak species. Soil samples were also collected in all study sites to analyze their chemical properties.
RESULTS AND CONCLUSIONS
We found higher concentration of Mg²⁺, NO3⁻ and SO4²⁻ in soils of sites with more proportion of orchards. Total leaf area, canopy cover and DBH, as well the herbivory and FA levels were higher in these sites and in the edges of fragments for both oak species. Chlorophyll content was higher at forest edges than in the interior of fragments for all sites analyzed. Leaves of both oak species were more elongated and wider in sites with more proportion of orchards, as well in forest edges. Plant traits, herbivory and FA were related to chemical soil properties according to the proportion of forest and orchards, indicating that the mechanisms driving this interaction are scale-dependent and vary among habitat types according to proportion of forest. Herbivory was positively correlated with leaf area, DBH, chlorophyll content and FA for both oak species, indicating that herbivory increase as resource availability and quality increased along mosaic of avocado agrosystems. Our results showed that land use change of forest to avocado orchards, creates fragments with intense edge effects changing chemical soil properties, which in turn affect quantity and quality of resources to insect herbivores, as well as leaf morphology and FA levels of Q. castanea and Q. obtusata individuals.
SIGNIFICANCE
Our study is the first to denote the importance of the maintenance and conservation of temperate forest ecosystems and their potential functional and ecological benefits to avocado cultivation.
Conversion from natural forest to timber plantation is an important cause of pristine forests loss. These changes alter community structure and cause a decrease in the diversity of plant communities. Leaf functional traits, which are an important defensive strategy, might also be influenced by such alterations. Altogether, shifts from natural forest to timber plantation may lead to profound changes in plant-plant and plant-animal interactions, including herbivory and the relative abundance of different feeding guilds, an important aspect of forest ecosystem function and community dynamics. In this study, we assessed insect herbivore damage in saplings of four native tree species in the understory of natural forests and two types of ca. 80-year-old timber plantations. We measured leaf damage by the most common feeding guilds in over 9000 leaves from 200 saplings. We first compared herbivory between natural forest and plantations, and we then analyzed the drivers of herbivory and of the two most common guilds-chewers and miners-using several indices of forest structure and leaf traits as predictors. Total herbivory did not change among forest types, but it showed some variation in two of the four species. Herbivory decreased with increasing species richness and increased with increasing basal area of conspecific and heterospecific trees. Leaf damage caused by chewers increased with leaf thickness, while damage caused by miners showed the opposite relationship. On an ecological level, our findings support expectations from the resource concentration hypothesis and on the role of leaf traits in mediating the impact of insect feeding guilds on leaf herbivory. On an applied level, these results suggest that timber plantations can support similar levels of ecosystem processes than natural forests decades after their establishment. Allowing the regeneration of a diverse understory in plantation forests should be implemented to favor ecosystem dynamics close to those of the original forests.
Tropical dry forests are among the most threatened ecosystems in the world. After habitat perturbation occurs, the habitat recovers naturally through ecological succession. This succession can modify functional attributes of plants, which in turn, can affect herbivorous insects’ performance. We analyzed morphological, functional, and chemical traits associated with herbivory patterns in Croton roxanae and C. suberosus, that occur in mature and secondary forests in the tropical dry forest of Chamela, Jalisco. Leaf area and leaf thickness were higher in secondary forest, while leaf density and fresh leaf mass were higher in mature forest. Dry leaf mass, specific leaf area, chlorophyll content, and water content showed variation between species in both forest conditions. The concentration of secondary metabolites showed variation between species and forest conditions. Croton roxanae showed higher herbivory in mature forest, and C. suberosus did not show differences between the two conditions. Leaves in secondary forest were slightly longer and broader than leaves in mature forest. Croton species showed higher fluctuating asymmetry in secondary forest. Herbivory was not associated with levels of fluctuating asymmetry levels in both Croton species. Our results suggest that plant attributes are influenced by forest condition, which in turn, indirectly affect the attack of herbivores.
1. Ants are recognized as induced biotic defence in mutualistic relationships with myrmecophytic plants. Pseudomyrmex concolor is an aggressive Amazonian ant that works as an anti‐herbivory agent for its host plant Tachigali myrmecophila. However, it is not known how this ant maintains the plant on low levels of herbivory.
2. Tachigali myrmecophila provides no food for P. concolor making this model appropriate to test the hypothesis that ants associated with myrmecophytes act as induced biotic defence by herbivory. Based on Optimal Defence Theory, we tested whether the response to herbivory and the ant daily activity rhythm is more frequent in most valuable parts of the plant, such as young leaves.
3. Ants were observed in young and mature leaves exposed to herbivory by experimental manipulation. Results suggest that ants act as induced biotic defence in T. myrmecophila: number of ants was significantly higher in manipulated leaflets, as well as the daily activity rhythm was increased in young leaves. The time to detect herbivory in young and mature leaves did not differ. However, leaf extracts signs were identified more quickly by the ants.
4. Induced ant responses in the ant–myrmecophytic plants system can be considered constitutive defence because ants are present throughout the development of their host plant from seedling to adulthood, responding aggressively to any intruder. In the Pseudomyrmex–Tachigali system, the presence of ants on the plants is, per se, a constitutive defence. However, the patrolling activity is an induced response, being the result of several plant‐related cues (chemical and physical) associated with herbivory activity.
Fluctuating asymmetry (FA) is widely used to quantify developmental instability (DI) in ecological and evolutionary studies. It has long been recognized that FA may not exclusively originate from DI for sessile organisms such as plants, because phenotypic plasticity in response to heterogeneities in the environment might also produce FA. This study provides the first empirical evidence for this hypothesis. We reasoned that solar irradiance, which is greater on the southern side than on the northern side of plants growing in the temperate zone of the northern hemisphere, would cause systematic morphological differences and asymmetry associated with the orientation of plant parts. We used geometric morphometrics to characterize the size and shape of flower parts in Iris pumila grown in a common garden. The size of floral organs was not significantly affected by orientation. Shape and particularly its asymmetric component differed significantly according to orientation for three different floral parts. Orientation accounted for 10.4% of the total shape asymmetry within flowers in the falls, for 11.4% in the standards, and for 2.2% in the style branches. This indicates that phenotypic plasticity in response to a directed environmental factor, most likely solar irradiance, contributes to FA of flowers under natural conditions. That FA partly results from phenotypic plasticity and not just from DI needs to be considered by studies of FA in plants and other sessile organisms.
Gradient of stressful conditions affect plant physiological and morphological traits. Previous studies have shown that plants located at higher altitudes might exhibit higher levels of both fluctuating asymmetry and leaf thickness. Although it is expected that higher fluctuating asymmetry levels should be accompanied by higher leaf consumption by herbivores, lower herbivory could be expected for elevated leaf thickness. Aiming to investigate this contradiction our objective was to determine the effects of altitude on fluctuating asymmetry and leaf thickness, and evaluate the importance of these two morphological traits on herbivory levels of Tibouchina granulosa Cogn. (Melastomatecea) in Brazilian Atlantic Forest. The study was conducted in southern Brazil, along a continuous altitudinal gradient raging from 1275 to 1950 m, where we measured fluctuating asymmetry, leaf thickness and herbivory from leaves of 29 individuals of T. granulosa. There was a positive effect of altitude on both fluctuating asymmetry and leaf thickness but only fluctuating asymmetry was related to herbivore. Our results suggest that as altitude increases plants face more stressful conditions, leading to higher fluctuating asymmetry. This may lead to a higher nutritional quality of leaves and herbivores may use leaf asymmetry as a cue for plant quality. The lack of a relationship between leaf thickness and herbivory gives us evidence that, in the studied location, leaf thickness is not primarily used as plant defense and probably has other functions related, for example, to water, solar radiation, and nutrient stresses. These results may be considered a baseline for the understanding on how altitudinal stress and potential herbivory pressure influence plant populations.
Plant development is influenced by several abiotic factors, which in turn influence morphological traits and life history. We investigated whether leaf area, herbivory, toughness, fluctuating asymmetry, structural complexity and the number of inflorescences of Palicourea rigida are influenced by sun/shade conditions or by Cerrado phytophysiognomy (typical cerrado or rupestrian field). We expected to find greater structural complexity, leaf toughness and more inflorescences in sun plants; shaded plants were expected to exhibit a greater degree of fluctuating asymmetry (an index of plant stress), reduced leaf toughness and greater herbivory. As for phytophysiognomies, we expected to find higher levels of leaf toughness and reduced structural complexity in plants from the rupestrian field. We sampled plants in the sun and shade from both phytophysiognomies. Leaf area, toughness, herbivory and fluctuating asymmetry, were influenced more by sun/shade conditions than phytophysiognomy; leaf toughness was the only variable to show greater values in conditions of sun. Our results indicate that exposure to sunlight is not a requirement for increased plant development, but plants in shade are experiencing stress, as shown by increased fluctuating asymmetry; increased leaf area, which is a strategy to compensate for lower light exposure for plants and higher herbivory, which depicts lower toughness.
For pioneer plants, shaded habitats represent a stressful condition, where sunlight exposure is below the optimum level and so leaves expand in order to intercept a greater amount of light. We investigated changes in both phenotypic variation and stress of Bauhinia brevipes in sunny and shaded microhabitats. Leaf area was used as a measure of phenotypic variation, whereas leaf asymmetry (difference between right and left sides of leaves), was used as a measure of stress. We hypothesized an increase in leaf area and stress in shaded locations, which might indicate that B. brevipes was compensating for low light absorption, and elevated levels of stress, respectively. Plants in the sun fitted a fluctuating asymmetry pattern (normal distribution of right minus left sides), while shaded plants were clearly antisymmetric (bimodal distribution of leaf side differences). Leaf asymmetry and area were 5% and 26.8% higher in plants in the shade compared to plants in the sun, respectively. These results were expected since B. brevipes is found predominantly in open areas; so sunlight exposure is important for its development. The presence of antisymmetry is rare in studies of developmental instability, and here it might indicate higher stress compared to plants with fluctuating asymmetry.
Herbivory is a main source of plant damage and injured plants might present decrements in nutrients, delayed growth and low reproductive outputs. Therefore, herbivory can be considered a stressful agent to plants. In this study, we investigated short-term changes in stress and nutrient levels of the invasive plant species Tithonia diversifolia (Asteraceae) after simulated herbivory. Parameters such as leaf fluctuating asymmetry (FA, a measure of plant stress, also known as developmental instability) and nitrogen levels were compared between control and treated plants reared in a greenhouse. We expected high levels of FA and significant changes in nitrogen in injured leaves. FA was assessed by measuring the right and left sides of leaves, from the leaf edge to the midrib, at the middle point of the leaves; nitrogen was evaluated through the Kjeldahl method. Though non-significant, at the end of the study, injured leaves were 22% more asymmetric than control leaves, and before-after comparisons revealed that FA increased by 33% in leaves after leaf damage. In addition, FA was positively and significantly related to leaf area loss. Nitrogen did not present changes after simulated herbivory. The control group showed non-significant changes in FA and nitrogen. FA was concluded to be a rapid estimator of plant stress following leaf damage, as during its short lifespan (45 days), leaves displayed tentatively increased developmental instability. We consider that leaf damage is a predictor of plant developmental instability and that FA can be used to detect and compare stress levels in plants after herbivory damage.
Water stress alters the plant and its thermal environment so that droughted plants become progressively more susceptible (through erosion of their defences) and suitable (through enhancement of certain traits) to their adapted consumers, allowing the latter to achieve faster growth, higher survival and more realised reproduction. Morphological, spectral, thermal, physiological and biochemical changes are identified which may be of relevance to herbivores. Outbreak insects include phloem feeders (Coleoptera), leaf feeders (Lepidoptera, Hymenoptera, Orthoptera), and sap suckers (Homoptera). Implications of changes in plant water deficit are shown for insect behaviour, insect physiology and insect regulation capacity. -from Authors
Plants do not offer homogeneous supplies of the resources required by herbivorous insects as many resource traits show considerable variation both within and between plants. The distribution of variation among host-plant attributes determines the optimal spatial resolution level for insect females to select the best resource patches for oviposition. In this study, we examine whether variation in fluctuating asymmetry and size of Erythroxylum tortuosum Mart. (Erythroxylaceae) leaves influence oviposition of the specialist leaf-miner Agnippe Chambers (Lepidoptera: Gelechiidae). By partitioning the variance across five hierarchical levels, the oviposition pattern was investigated at the spatial resolution level where these leaf traits varied the most. We confirm that the largest variation in both these leaf attributes occurs at the leaf level. We hypothesise that leaf-miner females will respond to this variation by selecting the best leaves (resources) on which to lay their eggs. We find that the probability of oviposition is not significantly related to fluctuating asymmetry or to leaf size (oviposition preference test), suggesting that these two physical traits are not relevant to leaf-miners as indicators of resource patch quality. Therefore, although we show that females laid significantly more eggs on larger leaves, this behaviour appears not to be a result of active selection of leaves. Our results suggest that Agnippe females probably adjust their oviposition proportionally to leaf area because the relationship between egg density and leaf area was not statistically significant.
1. Morphological characters of Salix borealis were monitored during 1994-96 at 10 sites along a transect crossing the heavily polluted surroundings of Severonikel smelter in NW Russia, and analysed with respect to pollution load and density of the principal herbivore, the leaf beetle Melasoma lapponica. 2. Leaf size and shoot growth increased and leaf pubescence decreased with an increase in pollution, whereas variation in other characteristics was not related to pollution load. 3. Leaf fluctuating asymmetry (FA) and leaf pubescence increased with an increase in herbivory, whereas variation in other characters was not related to foliar damage. 4. A field experiment demonstrated that leaf FA and pubescence were high in the year after defoliation. 5. The data on leaf FA, a non-specific stress indicator, suggest that for the extant individuals of S. borealis, defoliation resulted in detectable stress, whereas long-lasting severe pollution by sulphur dioxide and heavy metals caused no measurable stress response and may even stimulate growth of leaves and shoots. 6. Leaf FA of woody plants may serve as an early indicator of the biotic stress caused by herbivory, which expands the use of FA as a tool in helping to compare the relative strengths of different stressing agents.
Mound and Marullo's aim in producing this book initially was to be an introduction to the Thysanoptera of Costa Rica. The extensive distribution of these small insects caused the authors to extend the geographical area covered and review the Neotropical thrips fauna at family and genus level as there are no available comprehensive publications. The family classification for the suborder Terebrantia is that adapted by Mound, Heming and Palmer (1980). The suborder Tubulifera is exceptionally difficult, and all authors are not in agreement in their respective classifications. Gauld and Mound (1982), Crespi (1993), and Mound and Cresi (1994) are followed here. All areas reported on are not equally known, and faunal comparisons are not given. Some of the more serious pests are listed, and flight, dispersal, and seasonal wind systems are discussed. Sex ratios and polymorphism, life cycles, body structures, phylogeny, family classification, habitat association, and collecting, as well as microscope slide preparation, are included in the introduction.
Ovipositing adult females of myrmecophilous lycaenids are expected to select plants based on ant presence in order to maximize the survivorship of immature stages. Usually, larvae feed ants with honey-like solutions and, in turn, ants ward off parasitoids. Nonetheless, a rarely investigated approach is whether ant partners can also extend their protective behavior towards lycaenids eggs. Here, we investigated the ant-related oviposition pattern of Allosmaitia strophius and Rekoa marius; then, we compared egg parasitism according to the presence of ants. Lycaenid oviposition and egg parasitism (in percent) were experimentally compared in ant-present and ant-excluded treatments. The study plant, Heteropterys byrsonimifolia, is an extrafloral nectaried shrub which supports several ant species. We sampled 280 eggs, of which 39.65 % belonged to A. strophius and 60.35 % to R. marius. Both lycaenids eggs were significantly more abundant on branches with ants, especially those with Camponotus crassus and Camponotus blandus, two ant species known to attend to lycaenids. A. strophius and R. marius parasitism was 4.5- and 2.4-fold higher, respectively, in ant-present treatments, but the results were not statistically significant. Our study shows that ant-mediated host plant selection in lycaenids might be much more widespread than previously thought, and not restricted to obligate myrmecophilous species. Tending ants may be inefficient bodyguards of lycaenid eggs, because unlike larvae which release sugared liquids, eggs do not offer obvious rewards to ants. Ants can ward off parasitoids of larvae, as observed elsewhere, but our findings show that positive ant-lycaenid interactions are conditional and depend on immature ontogeny.
Herbivores are attracted to young shoots and leaves because of their tender tissues. However, in extrafloral nectaried plants, young leaves also attract patrol-ling ants, which may chase or prey on herbivores. We
examined this scenario in extrafloral nectaried shrubs of Banisteriopsis malifolia resprouting after fire, which promoted both the aseasonal production of leaves and the activity of extrafloral nectaries (EFNs). Results were compared between resprouting (burned) and unburned control plants. The aggressive ant species Camponotus crassus and the herbivorous thrips Pseudophilothrips obscuricornis were respectively rapidly attracted to resprouting plants because of the active EFNs and their less sclerophyllous leaves. The abundance of these insects was almost negligible in the control (unburned) shrubs. Ants failed to protect B. malifolia, as no thrips were preyed upon or injured by ants in resprouting plants. Consequently, on
average, 37 % of leaves from resprouting shrubs had necrosis marks. Upon contact with ants, thrips released small liquid droplets from their abdomen, which rapidly displaced ants from the surroundings. This study shows that P. obscuricornis disrupted the facultative mutualism between C. crassus and B. malifolia, since ants received extrafloral nectar from plants, but were unable to deter herbivore thrips.
Plants are able to compensate for loss of tissue due to herbivores at a variety of spatial and temporal scales, masking detrimental effects of herbivory on plant fitness at these scales. The stressing effect of herbivory could also produce instability in the development of plant modules, and measures of such instability may reflect the fitness consequences of herbivory if instability is related to components of plant fitness. We analyse the relationships between herbivory, developmental instability and produc-tion of female flowers and fruits of holm oak Quercus ilex trees by means of herbivore removal experiments. Removal of leaf herbivores reduced herbivory rates at the tree level, but had no effect on mean production of female flowers or mature fruits, whereas herbivory tended to enhance flower production and had no effect on fruit abortion at the shoot level. Differences in herbivory levels between shoots of the same branch did not affect the size and fluctuating asymmetry of intact leaves. These results indicate compensation for herbivory at the tree level and over-compensation at the shoot level in terms of allocation of resources to female flower production. Removal of insect herbivores produced an increase in the mean developmental instability of leaves at the tree level in the year following the insecticide treatment, and there was a direct relationship between herbivory rates in the current year and leaf fluctuating asymmetry the following year irrespective of herbivore removal treatment. Finally, the production of pistillate flowers and fruits by trees was inversely related to the mean fluctuating asymmetry of leaves growing the same year. Leaf fluctuating asymmetry was thus an estimator of the stressing effects of herbivory on adult trees, an effect that was delayed to the following year. As leaf fluctuating asymmetry was also related to tree fecundity, asymmetry levels provided a sensitive measure of plant performance under conditions of compensatory responses to herbivory.
In Brazil, almost nothing is known about the thrips fauna associated with rice crops. This is especially true for Rio Grande do Sul State (RS), the major rice producer in Brazil, where no systematic surveys have been conducted. Thus, this work records preliminarily the species of suborder Terebrantia inhabitanting irrigated rice (RC) and three nearby habitats: the area selected for rice, before cultivation (BR), grassland (GR) and forest border (FB) in Cachoeirinha, RS (50º58'21"W; 29º55'30"S). Eight field trips were carried out between October/2004 and February/2005 to Estação Experimental do Arroz in Cachoeirinha. Thrips specimens were collected with sweeping net and transported to laboratory for identification. A total of 623 adults terebrantians were recorded, belonging to two families and 18 species. Frankliniella rodeos (55.5%), Neohydatothrips cf. paraensis (30.3%) and Frankliniella schultzei (5.6%), were the most abundant, comprising more than 90% of the individuals. FB showed the highest species richness (S=15), followed by GR (S=10), RC (S=9) and BR (S=6). FB presented a low number of individuals (14.0%), contrasting with GR (44.8%) and BR (36.7%). In general, thrips abundance in RC was low at EEA (4.5%), and few species seems to effectively use rice as a host-plant. Two species previously considered of economic importance were found, F. rodeos and F. schultzei, the latter a new record for rice in Brazil. Five species are new records to RS.
Reintroduced environments represent stressful conditions to plants that can be observed in different ways. We evaluated the relationships between fluctuating asymmetry (FA), herbivory, and plant ontogeny of Chamaecrista semaphora (Fabaceae) under natural and restored habitat conditions. The patterns of leaf FA and herbivory by folivorous insects (chewing) on saplings and mature plants in each habitat were determined. No relationship was found between FA and herbivory on the two ontogenetic stages in both environments, suggesting that FA did not represent an indicator of stress. The frequency and amount of leaf area removed by folivores were higher in saplings compared to adult plants under the natural habitat, while the opposite trend was observed on restored habitat for adult plants. The restored habitat did not represent an environmental stress condition to C. semaphora, indicating that this endemic plant may represent a good candidate to restoration programs in harsh environments. However, we observed great differences in leaf FA and herbivory among individuals within habitats. Knowledge on plant quality, competition, physiology, and interactions with natural enemies are highly needed to support long lasting programmes on restoration of harsh environments.
Leaf fluctuating asymmetry (FA) is an important indicator of plant responses to various sources of stress, which range from poor nutritional and harsh environmental conditions to herbivory and parasitism. Mistletoes are important hemiparasites, which represent a source of stress for their host plants but, in spite of being common in all major biogeographical regions of the world, no study has measured the response of their hosts in terms of leaf FA. We addressed the effect of mistletoes on host–plant foliar FA by comparing parasitized and non-parasitized individuals of four host species in two sites in southeastern Brazil, Serra do Cipó and Serra do Rola Moça. In the four host species, parasitized individuals presented significantly higher levels of leaf FA than unattacked plants. The specialist mistletoe Phoradendron cf. amplexicaule induced higher levels of FA on its host Erythroxylum suberosum (Erythroxylaceae) than the generalist mistletoe Struthanthus flexicaulis did on either Mimosa calodendron (Fabaceae), Lychnophora pinaster (Asteraceae) or Stachytarpheta glabra (Verbenaceae). We hypothesized that specialized parasites could be more damaging to their hosts than generalist mistletoes, which could explain the higher FA levels observed. Significant differences in FA levels among parasitized individuals within species were found, which were significantly correlated with intensity of infection (number of mistletoes per host individual). The results indicate that mistletoes represent an important factor of stress for their host plants, and that FA can be an excellent instrument for evaluating the effects of infections by parasitic plants.
Seis espécies de Frankliniella: F. brevicaulis Hood, F. condei John, F. occidentalis (Pergande), F. schultzei (Trybom), F. williamsi Hood e F. zucchini Nakahara & Monteiro são consideradas pragas no Brasil, sendo três delas vetoras de viroses. Uma chave para diferenciar essas espécies é apresentada, assim como sua caracterização morfológica.
Fluctuating asymmetry (FA) represents small, random variation from symmetry, and it has been used as an indicator of plant stress at relatively local scales. In this study, variation in FAwas examined at the landscape scale across the whole distributional range of the two oak species Quercus myrtifolia and Quercus chapmanii in Florida. Oak leaf morphology was evaluated in 40 sites covering ∼170,000 km 2. Plants growing on coastal/edge sites exhibited significantly higher levels of FA than did plants inhabiting inland/center sites. For myrtle oaks, levels of FA were also spatially structured, and sites were positively spatially autocorrelated at small distances, indicating that sites that were closer exhibited similar levels of environmental stress and FA. Our results have shown that FA, a reliable measurement of plant stress at local scales, can also be used as a biological tool for monitoring the quality of the environment at larger spatial scales, increasing its usefulness in studies across the full range of plant species.
Two widely different classifications of the insect order Thysanoptera are discussed; an essentially phylogenetic system recognizing nine families in two suborders, and an essentially phenetic system recognizing 40 families in two orders. This paper emphasizes the distinction between "classification" and "systematics", the former stressing the importance of differences, whereas the latter stresses the importance of derived similarities. A phylogenetic (i.e. systematic) classifica- tion incorporates predictions concerning evolutionary relationships that are important throughout biological studies, whether in host and parasite associations, biogeography, comparative physiology or development. The available phenetic classification of Thysanoptera serves no such broader purpose in biology. Recent molecular data derived from the gene 18S rDNA are analysed, but although some groups of taxa are well resolved, the deep relationships within the Thysan- optera remain unclear.
Plants are ideal organisms for studying genotypic and environmental influences on developmental stability. Because they may have numerous leaves, flowers, and stems, one can study variation in developmental stability in a single individual. Moreover, one often has sufficient degrees of freedom to test for differences in devel- opmental stability among individuals. Nevertheless, within-plant variation in developmental stability can be a potential problem. Leaf size and asymmetry in the common fig, Ficus carica, vary within a plant, depending on height (lower, middle, top) and position (inside, outside). Leaves from the outside top are the largest, and those from the inside bottom are the smallest. Outer leaves, which may experience greater stress from cold, heat, sunlight, and desiccation, are more asymmetrical than inner leaves. We also found significant differences in leaf asymmetry among plants.
Fires in the Cerrado savanna are a severe form of disturbance, but some species are capable of resprouting afterwards. It is unknown, however, how and whether post-fire resprouting represents a stressful condition to plants and how their rapid re-growth influences both the production of biochemical compounds, and interactions with mutualistic ants. In this study, we examined the influence of post-fire resprouting on biotic interactions (ant-plant-herbivore relationships) and on plant stress. The study was performed on two groups of the extrafloral nectaried shrub Banisteriopsis campestris (Malpighiaceae); one group was recovering from fire while the other acted as control. With respect to biotic interactions, we examined whether resprouting influenced extrafloral nectar concentration (milligrams per microliter), the abundance of the ant Camponotus crassus and leaf herbivory rates. Plant stress was assessed via fluctuating asymmetry (FA) analysis, which refers to deviations from perfect symmetry in bilaterally symmetrical traits (e.g., leaves) and indicates whether species are under stress. Results revealed that FA, sugar concentration, and ant abundance were 51.7 %, 35.7 % and 21.7 % higher in resprouting plants. Furthermore, C. crassus was significantly associated with low herbivory rates, but only in resprouting plants. This study showed that post-fire resprouting induced high levels of plant stress and influenced extrafloral nectar quality and ant-herbivore relationships in B. campestris. Therefore, despite being a stressful condition to the plant, post-fire resprouting individuals had concentrated extrafloral nectar and sustained more ants, thus strengthening the outcomes of ant-plant mutualism.
We surveyed a Cerrado and Riparian Forest vegetation area located at São Carlos Federal University (21°58’
S, 47°51’ W). The objective of the survey was to provide a full inventory of the area’s angiosperm flora. This inventory was conducted in a region in which few remnants of Cerrado and Riparian Forest are left because of the destruction of these habitats to provide land for sugar cane and citrus cultivation. We identified 188 species. These species belong to 140 genera and 55 families. We obtained images of 117 species, including details of inflorescences, flowers and fruits, to support our identifications. These results highlight the importance of the preservation of this reserve because the area offers a species-rich flora in a location where few fragments of native vegetation exist and because the area could be of interest for establishing ecological corridors.
In the Brazilian savanna many plant species bear regular associations with patrolling ants that are aggres-sive towards insect herbivores. However, not only ants but also several species of predatory wasps are
attracted to plants due to the extrafloral nectaries (EFNs). Such wasps feed on both herbivores and plant
exudates. In this study we describe the foraging behavior of the social Polistinae wasp Brachygastra
lecheguana in the extrafloral nectaried shrub Banisteriopsis malifolia, and investigated the influence of
patrolling antsCamponotus blanduson the activity of the wasp.Brachygastra lecheguanafed on the
endophytic larvae ofAnthonomus(Curculionidae) beetles that developed inside flower buds. The wasp
lacerated the bud layers to reach the beetle larvae located at the bud core. The wasp visits to Ba. malifolia
were statistically related to the abundance of flower buds and beetles. Ant exclusion experiments revealed
that the hunting behavior of B. lecheguanaon beetles was not related to the absence ofC. blandus.
However we found that wasps spent more time consuming extrafloral nectar on branches where ants were
excluded. This is the first study reporting extrafloral nectar consumption byB. lecheguana, as well as the
predation on herbivores in natural areas. In cerrado vegetation, ants benefit the plant by reducing insect
herbivores, and our study provides evidence that theB. lecheguana – Ba. malifoliasystem represents a
potential interaction where the wasp may also benefit the host plant. The value of this wasp species as a
plant-guard is discussed.
Fluctuating asymmetry (FA) can be defined as small, random deviations from bilateral symmetry in structures that are bilaterally symmetrical and can estimate a population's inability to buffer its growth against perturbations of environmental origins. Another important issue about FA is whether biotic factors may also induce stress in organisms. Therefore, in this study I aimed to investigate the influence of both the abiotic (light exposure) and biotic (Ditylenchus sp. galls) factors accounting for increased FA in Miconia fallax leaves. Galls are known as parasites and a major cause of leaf stress. Additionally, since M. fallax is a pioneer plant species, individuals in the shade were supposed to present high levels of FA relative to plants on the edges exposed to direct sunlight. Results showed no concomitant interaction between gall abundance, light exposure and FA. Separate analysis showed that plants in the shade presented the highest level of FA, almost 25% higher than plants on the edges, indicating that plants growing in places with little sunlight were in stressful condition. The presence of galls did not cause alterations in FA relative to leaves without galls. The lack of relationship between galls and leaf FA indicates that M. fallax can tolerate and buffer the presence of these leaf parasites, revealing the high homeostasis ability of this plant species against a biotic stress.
Keywords: edge effect, light exposure, pioneer plant, Cerrado
Although very abundant in the Neotropics, there is little information about the biology, ecology and natural history of Brazilian Chlamisinae beetles. In the present study we investigated directly in the Cerrado vegetation the aspects of natural history and biology of Chlamisus minax Lacordaire. The results showed that the species has annual cycle and the adults are present in the field during the spring and summer when the reproduction occurs. The females cover their eggs with a mantle, and later on the rests of the egg and faeces are added by the larva to the mantle to produce a protective case. The six larval morpho-stages are herbivorous and feed on floral buds of Heteropterys pteropetala A. Juss. (Malpighiaceae). The larvae pupate in the host plants and after that they fall on the ground remaining in diapause between April and October. This is the first study to investigate the biology and natural history of a Brazilian Chlamisinae beetle directly in the field.
Heterothrips peixotoa Del-Claro, Marullo and Mound is described as new. It has remarkably pale forewings, and lives in the flowers of a malpighiaceous shrub in Brazilian cerrado. The sepals of each flower are S-shaped and enclose a central cavity within which the thrips live and breed. Although some large ants are unable to penetrate this cavity, other ants are small enough to enter the space between the petals and sepals, and this leads to a reduction in thrips numbers. Several other members of this genus of thrips are known from the flowers of other species of Malpighiaceae.
A technique for rearing large numbers of the thrips P. ichini, an approved biological control agent for Brazilian peppertree, was developed. This rearing method facilitated laboratory host range testing that was required for obtaining approval for field release in Florida. The procedure will be used for mass rearing the insect to provide sufficient numbers of insects for the initial field releases at several Florida locations.
Leaf fluctuating asymmetry (FA) is considered an important indicator of environmentally induced stress in plants, but the relationship between herbivory and FA levels is not clear. In this study we compared leaf size and shape, leaf area consumed by herbivorous insects, and FA levels between individuals of Heliocarpus pallidus (Tiliaceae) from two adjacent and contrasting habitat types (deciduous and riparian) in the Chamela-Cuixmala tropical dry-forest biosphere reserve. Ten individuals of H. pallidus were collected in each habitat type. Leaf shape was assessed using geometric morphometric techniques. Results indicated statistically significant differences in leaf shape between individuals from the two habitat types. In individuals from the riparian habitat leaf area (mean = 42.3 +/- 1.2 cm(2)), herbivory levels (mean = 25.5% +/- 1.8%) and FA levels (mean = 0.38 +/- 0.04 cm) were significantly higher than in individuals from the deciduous habitat (17.2 +/- 3.5 cm(2); 9.6% +/- 1.0% and 0.18 +/- 0.04 cm, respectively). Within habitats, significant correlations were found between total leaf area and percentage leaf area removed by insects (R-2 = 0.92 in riparian habitats, R-2 = 0.9 in deciduous habitats), and between percentage leaf area removed and FA (R-2 = 0.70 in riparian habitats, R-2 = 0.79 in deciduous habitats). As has been suggested for other plant species, it is possible that the more favourable conditions in the riparian habitat enhance leaf growth, resulting in higher FA. Also, individuals in this habitat might be characterized by lower chemical defence and/or higher nutritional quality, which would explain the higher herbivory levels.
Although the terminology used in studies of developmental instability refers explicitly to development, this field of research has largely existed in isolation from mainstream developmental biology. Here I review the theory and models concerning fluctuating asymmetry (FA) with respect to the developmental mechanisms they assume. Some of the published models deliberately do not refer to developmental mechanisms at all, but are purely phenomenological models designed to examine statistical questions relating to FA. Other models are based on the dynamics of reaction–diffusion processes, and interpret the resulting oscillations in reactants as an analogue to the source of FA, and another model includes simplified model of both a developmental process and its genetic control. These studies emphasize the importance of feedback mechanisms and of nonlinear dynamics of developmental processes, and illustrate that fairly simple models are sufficient to generate patterns similar to those observed in empirical studies. In recent years, a number of models for stochastic switching of gene expression have been developed, which provide a possible explanation for developmental noise. Moreover, mechanisms such as gene duplication and stabilization of proteins by molecular chaperones possibly provide developmental stability, but many more are probably involved. These molecular models, which hold many possibilities for experimental studies of the mechanisms involved, point toward a promising new approach to understanding developmental instability that can reunite this field with developmental biology.
Fluctuating asymmetry (FA), random nondirectional deviations from perfect symmetry, has been proposed as a useful indicator of environmental stress. Nevertheless, FA acts as a nonspecific indicator of stress; thus, factorial designs are needed to disentangle which of the factors may induce FA. We used an experimental approach in which seedlings of Quercus pyrenaica were exposed to two levels of light, water, and simulated herbivory. To determine whether FA may operate as a stress indicator, leaf width and number of lobes were measured. Our predictions were (1) different levels of light, water, and herbivory can bring different levels of FA and (2) fluctuating asym-metry can act as an early stress indicator. As predicted, FA was higher in shade than in sun, both for leaf width and number of leaf lobes. By contrast, pruning affected FA only for number of lobes. FAwas higher in pruned seedlings in the sun but lower in pruned seedlings in the shade. The two FA indices used (jL À Rj and Var L À R ð Þ, where L and R represent the left and right leaf sides) gave similar results. Because leaf FA in Q. pyrenaica increased with low light radiation and simulated herbivory and both are important in the dynamics of Mediterranean communities, FA appears to be a possible tool as an indicator of environmental stress.
An outbreak of leaf beetle Melasoma lapponica in two localities around the Severonikel smelter in Kola Peninsula, north-west Russia, resulted in severe defoliation of
Salix borealis, observed for the first time in August 1993 and then again in 1994 and 1995. Before the first severe defoliation, in July
1993, performance of M. lapponica larvae in plots with a high beetle density was either better or the same as in low-density plots. However, in 1994 and 1995,
the years following severe willow defoliation in high-density plots, M. lapponica performance (in terms of survival, developmental time and beetle weight) decreased with increasing beetle density. Retarded
larval growth in high-density plots was related to a decreased consumption rate, whereas the efficiency of the conversion
of ingested food was similar in high- and low-density plots. These results indicate that defoliation triggered delayed induced
resistance in S. borealis. Leaf fluctuating asymmetry (FA, a non-specific stress indicator) of this willow species in 1992 was similar in low- and
high-density plots, but it increased in high-density plots in 1994, at the same time that detrimental effects on beetle performance
were recorded at these sites. Plot-specific indices of beetle performance and FA were negatively correlated both in 1994 and
1995, suggesting that plants stressed by defoliation the previous-year were less favourable for leaf beetles.
It is suggested that descriptive taxonomy of thrips must be integrated into biological studies if we are to understand patterns of evolutionary and ecological diversity. Collecting and describing new taxa is easy, but understanding their position in ecosystems and how they have contributed to the origin and maintenance of biological diversity is more important yet more difficult. Many authors fail to appreciate that individual thrips species are commonly highly polymorphic, both within and between sexes, with the result that 20% of species names and 30% of generic names are currently placed into synonymy. The biological significance of such polymorphism has been little studied, but the presence of large and small males in a species is presumed to indicate some form of male/male competition for resources; this is particularly common in fungus feeding species. Amongst phytophagous species, the recognition of the host plants on which thrips actually breed is a prerequisite to understanding patterns of diversity, some thrips lineages being associated with particular groups of plants whereas others exploit a diverse range of plants. Attempts to understand the diversity of thrips, including the application of cladistic methods, are severely limited by the lack of studies on the biology of individual species, although thrips exhibit a wide range of interesting biological phenomena, including various levels of sociality, gall-induction, specific pollination associations, virus transmission, and ectoparasitism.
We investigated how the pattern of leaf damage influences reproduction, growth, and allocation in the wild radish, Raphanus sativus (Brassicaceae). We removed an equivalent leaf area from plants with four leaves in five treatments ranging from concentrated to dispersed damage: one entire mature leaf removed, on entire new leaf removed, 50% of two mature leaves removed, 50% of two new leaves removed, and 25% of all four leaves removed. Plants in a control group were undamaged. Reproduction, growth, and allocation were not affected by the age of the damaged leaf. However, the pattern of leaf damage significantly affected our three measures of plant fitness: the number of flowers produced, the reproductive biomass, and the total biomass. Plants in the treatment in which the damage was most dispersed had significantly higher flower number, reproductive biomass, and total biomass than an intermediate damage treatment and significantly more reproductive biomass than the concentrated damage treatment. There were no significant differences between the concentrated and intermediate damage treatments and no differences between the dispersed damage treatment and the undamaged control. Our data indicate that more dispersed damage is less detrimental to the plant than more concentrated damage. Therefore, the pattern of leaf damage must be considered in determining the impact of herbivores on plant performance.
Assessed the effects of the three most abundanct herbivores (a thrips Apterothrips apteris, a spittlebug Philaenus spumarius and plume moth caterpillars Platyptilia williamsii on growth and reproduction of their long-lived, iteroparous host plant. Thrips reduced root biomass of seedlings, but not a shoot biomass. No correlation was found between density of thrips and change in aboveground area of plants after monitoring for three years in the field. Thrips fed on the phyllaries and corollas of flower heads, as well as on leaves, and were particularly damaging to ray petals. Plants in a common garden were subjected to three seasons of feeding by either spittlebugs, plume moth caterpillars, both, or neither. Plant survival was unaffected by these insect herbivores, although gophers Thomomys bottae were a major source of mortality. Plants with caterpillars produced more rosettes than those without moths. By consuming apical buds the caterpillars released axillary buds, thereby causing plants to produce more side rosettes. This difference in architecture did not result in an increase in flower production. Plants that had experienced three years of spittlebug or caterpillar attack produced fewer flower heads than controls during their third year. One year later, and after the herbivory treatments were discontinued, plants that had been damaged by spittlebugs still produced fewer flowers than those in other treatments. -from Authors
1. Fluctuating asymmetry, which represents small, random deviations from bilateral symmetry, arises as a result of an inability to control development under genetically and environmentally stressful conditions. Herbivory is also particularly common in plants growing under stressful conditions. It was hypothesized that herbivory would be particularly prevalent in plants with leaves demonstrating high degrees of fluctuating asymmetry. This prediction was tested for the leaf-mining insect, Rhynchaenus rufus, which commonly attacks elm Ulmus glabra. 2. Leaves with mines were significantly more asymmetrical in the width of their two halves and the distance between side-ribs, than the nearest neighbouring leaf without a mine. Elm trees with a high incidence of leaf mines had significantly more asymmetric leaves than the nearest neighbouring elm tree with a low incidence of leaf mines. This was the case regardless of whether affected or unaffected leaves were compared. 3. The incidence of leaf mines across trees was positively related to the degree of leaf asymmetry of the tree. Developmental stability of leaves, as measured by fluctuating asymmetry, was therefore associated with susceptibility to one kind of herbivory in elm trees. 4. Leaves of elm trees watered with a large amount of fertilizer were more asymmetric than leaves of trees just provided with water, suggesting that one kind of stress increased the level of leaf asymmetry. The relationship between foliar asymmetry and herbivory appeared to be causal since increased asymmetry caused by the fertilizer treatment gave rise to an increased abundance of leaf miners.
Fluctuating asymmetry (FA) is defined as small and random deviations from perfect symmetry in otherwise bilaterally sym-metrical traits. Usually, plants under stress have a higher nutritional quality and are preferred by insect herbivores. Here, we examined the relationship among leaf FA of Bauhinia brevipes (Fabaceae), nutrients and the occurrence of Schizomyia macrocapillata (Cecidomyiidae: Diptera). We evaluated whether: (i) FA was related to S. macropillata abundance and survivorship; (ii) FA correlated with the levels of foliar nutrients (macro- and micronutrients, and organic carbon); and (iii) S. macropillata abundance was related to leaf nutrients. The results showed a positive relationship between FA and gall abundance. S. macro-capillata survivorship was five times higher in B. brevipes individuals with high FA levels, but this difference was not significant.
The influence of nutrients in B. brevipes FA was negligible, except for foliar nitrogen, which was 7.3% higher in plants with low FA levels. The abundance of S. macrocapillata was negatively related to nitrogen levels, but gall survivorship was not affected by this nutrient. We found evidence for a causal relationship between FA and gall occurrence, since S. macropillata gall oviposition occurs in young undeveloped leaves, thus mature leaves show an increase in FA. Nonetheless, in this system,neither FA nor nitrogen influenced gall survivorship.
1. Fluctuating asymmetry (FA) of birch leaves collected along four pollution gradients in NW Europe was assessed by measuring the difference in width between right and left halves of the leaf. 2. FA of leaves was not related to tree diameter, and values for long and short shoots of the same tree were correlated. 3. FA of silver birch Betula pendula and two subspecies of B. pubescens, white birch B. pubescens ssp. pubescens and mountain birch B. pubescens ssp. tortuosa, decreased hyperbolically with distance away from four sources of aerial emission which differed in amounts and composition of pollutants. 4. The extent of the zone of increased FA was higher around polluters which produced more emissions. 5. FA of leaves sampled around two copper-nickel smelters was positively related to foliar nickel concentrations, and regressions from these two sites had similar slopes and intercepts. 6. The data suggest that FA of birch leaves may represent a convenient indicator for rapid assessment of environmental quality.
The effect of feeding by the Russian wheat aphid, Diuraphis noxia (Mordvilko), on growth of seedling 'TAM W-lOl' winter wheat (Triticum aestivum L.) was investigated. A primary response of the wheat plant to aphid feeding involves water imbalances expressed as a loss of turgor and reduced growth. Russian wheat aphids caused substantial reductions in biomass of all plant components measured. When aphids were removed, absolute growth rates quickly recovered as relative growth rates increased. Compared with undamaged controls, recovering plants were more efficient in terms of carbon assimilation, which resulted in higher relative growth rates and compensated for lowered leaf area ratios. Reduction in leaf area ratios results from decreases in specific leaf areas (i.e., a combination of leaf stunting and the inhibition of new-leaf unfolding). As plants recovered, stem weight ratios were substantially reduced, indicating that carbon partitioning to the stem was decreased to compensate for leaf and root growth. The cessation of growth of wheat during infestation by the Russian wheat aphid and ability of the host to recover rapidly when the aphid was removed indicate that the duration of infestation, rather than the level of infestation, may be more important to the host.
PDA calculated via image analysis provides an objective, quantitative measurement of cumulative direct feeding damage from WFT compared to subjectively-assigned quality ratings. The results from the image analysis method were well correlated to thrips density. The image analysis method can be used in nearly any research where arthropod feeding damage results in lesions or localized color changes in plant foliage.
Megalurothrips sjostedti (Trybom) is an important pest of cowpea (Vigna unguiculata) in West Africa. Three key factors assumed to be responsible for its pest status are analysed, the survival on alternative host-plants during the dry season, the inefficient biotic mortality factors regulating population growth, and the effect of larval feeding on the development of cowpea flower buds. Extensive surveys indicate clearly that M. sjostedti survives the dry season on a wide range of alternative hosts all belonging to the Leguminosae, where it can feed and reproduce. Different antagonists were observed attacking eggs and larvae of M. sjostedti; their impact, however, is low and cannot prevent pest outbreaks. Two undescribed Megaphragma spp., and one Oligosita sp., all trichogrammatid egg parasitoids, were recorded for the first time. The anthocorid Orius sp. was the most important larval predator. No hymenopterous parasitoids could be reared from larvae collected on cowpea and three major alternative hosts, whereas a low percentage of the larvae collected from the flowers of Tephrosia candida, an exotic shrub native to India, were parasitized by the eulophid Ceranisus menes (Walker), also recorded for the first time in Africa. The feeding activity of six larvae of Megalurothrips sjostedti during five days induced the shedding of all flower buds of a cowpea inflorescence. The results of the analysis shed new light on the M. sjostedti pest problem, and the ways to solve it. The lack of efficient antagonists, particularly larval parasitoids known from closely related south-east Asian Megalurothrips spp., and the high damage threshold, indicate that M. sjostedti is a potential target for biological control. However, further studies are needed to investigate the migration of M. sjostedti adults to and from alternative host-plants, in order to reinforce the action of biocontrol with cultural pratices.
It has been suggested that plant physical and chemical traits vary considerably in space and time. Hence, leaf-mining insects may adjust their oviposition in response to leaf attributes representing high quality. Moreover, herbivorous insects can modify leaf morphology by acting as stressors, increasing, for example, fluctuating asymmetry (FA) levels. Here, we investigate oviposition preference in Agnippe sp.2, a leaf-mining moth of Erythroxylum tortuosum, in relation to differences in leaf nutritional quality (i.e. levels of water, nitrogen and tannin content), leaf area (i.e. quantity of resource hypothesis) and FA. We also verify whether temporal variation in plant nutritional quality emerges as an alternative hypothesis to explain oviposition distribution in time, and whether this leaf miner is a stress-causing agent, increasing FA during larval development. Mined leaves and leaves with and without eggs were periodically collected from plants located in a Cerrado fragment in Brazil. In the laboratory, leaf traits were assessed (using image analysis software) and quantified (biochemical analysis) according to the aims previously determined. Oviposition probability did not change in relation to variations in nitrogen, tannins and FA of leaves. However, leaf-miner females preferred to oviposit on leaves having large areas and low water contents. It was also verified that new leaves of E. tortuosum, which carried most leaf-miner eggs, presented significantly lower tannins and greater levels of nitrogen and water than old leaves. The oviposition choice exhibited by leaf miners was found to be non-random because they appear to use resource quantity and water content as cues as where to lay their eggs. The temporal variation of plant nutritional quality is likely to influence the time of leaf-miner oviposition; and leaf FA was not increased during larval feeding, suggesting that these herbivores do not cause variations in FA levels.
Browsing and defoliation often increase the densities of insect herbivores on woody plants. Densities of herbivorous invertebrates were estimated in a long-term grazing manipulation experiment. More then 30-yr-old fences allow us to compare densities of invertebrate herbivores on Salix lanata in areas heavily grazed and areas lightly grazed by reindeer. The number of gall-forming insects (Pontania glabrifons) and gall-forming mites were higher on the heavily grazed shrubs than on lightly grazed shrubs. In contrast to most short-term studies, the heavily grazed S. lanata had shorter current annual shoots. No difference in leaf size, leaf nitrogen content, or C:N ratio between grazing intensities were detected. However, the enhanced natural δ15N value indicates that heavily grazed shrubs get a higher proportion of their N directly from reindeer faeces. Leaf weight per unit area and relative fluctuating asymmetry of leaf shape increased in heavily grazed S. lanata. Enhanced relative fluctuating asymmetry might indicate higher susceptibility to herbivores. Long-term grazing seems to increase the density of invertebrate herbivory in the same way as short-term grazing, even if the plant responses differ substantially.
Abstract 1 Since the late 1970s, the western flower thrips has spread from its original distribution in western North America to become a major worldwide crop pest.
2 A wide range of data sources have been used to map the original distribution in the U.S.A. and Canada, and the progress of the spread in the U.S.A., Canada, Europe, northern Africa and Australia.
3 The possible reasons for the start of the spread are discussed. The most likely reason is that intensive insecticide use in horticulture in the 1970s and 1980s selected an insecticide resistant strain or strains. These then established in glasshouses across North America and spread from there to Europe, Asia, Africa and Australia.
4 The international spread of the western flower thrips occurred predominantly by the movement of horticultural material, such as cuttings, seedlings and potted plants. Within Europe, an outward spread from the original outbreak in the Netherlands is discernible. The speed of spread was 229 ± 20 km/year.
5 The spread has not been restricted to glasshouses. The western flower thrips has established outdoors in areas with milder winters; for example, across the southern U.S.A., southern Europe and Australia. It also overwinters in some regions with colder winters.
6 Polyphagous phytophagous thrips have many factors predisposing them to become worldwide crop pests, particularly in glasshouses. Some other species that might spread in a similar way to the western flower thrips are listed.
The only 3 published studies relating vertebrate herbivores to plant fluctuating asymmetry (FA) found significant correlations between grazing intensity and plant FA. The general value of these early findings is unclear, however, because FA studies are sensitive to selective reporting, the tendency to publish only a subset of studies that were undertaken. From 2000 to 2003 we quantified the correlations between past herbivory and plant FA in 3 plant–herbivore systems centred on a single mammal species, the North American porcupine (Erethizon dorsatum). We measured leaf FA in pairs of paper birch (Betula papyriferae; n = 24 pairs), quaking aspen ( Populus tremuloides; n = 25 pairs), and jack pine ( Pinus banksiana; n = 15 pairs) trees each containing a control (uneaten) and test (eaten) tree. Although damage incurred by trees from porcupine browsing was severe, we found no statistical association between plant FA and herbivory. We obtained this finding even though our study design did capture subtle variations in plant FA associated to plant genotype or year of sampling. Our study contrasts with earlier findings that plant FA is related to herbivory pressure. There may have been a publication bias as a result of selective reporting in this field of research. Therefore, replication (same hypothesis, same study system) and quasireplication (same hypothesis, different study system) are particularly important.
It has previously been postulated that when plants are stressed by certain changes in patterns of weather they become a better source of food for invertebrate herbivores because this stress causes an increase in the amount of nitrogen available in their tissues for young herbivores feeding on them. And this may cause outbreaks of such phytophagous invertebrates.Evidence is now presented that a similar physiological mechanism appears to operate when a wide variety of apparently unrelated environmental factors impinge on plants or parts of plants in such a way as to perturb their metabolism. A broken branch, lightning strike, fire, nutrient deficiencies or an otherwise adverse site; all may have this effect. With the advent of modern man the available agencies increase and diversify to include pesticides, irradiation and air pollutants.One common metabolic response by plants to all such agents impinging on them seems to be equivalent to that found in senescing plant tissues — the breakdown and mobilization of nitrogen in soluble form away from the senescing/stressed tissues. Young herbivores which chance to feed on such stressed/senescing tissues have a greater and more readily available supply of nitrogen in their food than they would have had if feeding on unstressed plants. As a result many more of them survive, and there is an increase in abundance of their kind. Such increases may be quite localised and short-lived or more widespread and persistent, depending on the extent and duration of the stress experienced by the plants. And in the face of this improved nutrition and survival of the very young, predators and parasites seem to have only a minor influence on subsequent changes in abundance of their herbivorous prey.Another effect of increased mobilization of nitrogen in stressed plants is an increase in the quantity of the seed that they set. This has led to the conclusion that increased abundance of some species of birds at such times is due to a greater supply of seeds as winter food for recent fledglings. But it may be that the increased abundance is due to the synchronous increase in phytophagous insects providing a richer source of protein food for laying hens and growing nestlings.
The feeding behavior of Diuraphis noxia Mordvilko (Homoptera: Aphididae) on susceptible hosts causes both ultrastructural and tissue level damage which may affect phloem composition. Genetic evidence suggests that endosymbiotic bacteria in most aphids overproduce limiting amino acids to benefit hosts but that D.noxia depends less on endosymbionts for these nutrients, possibly due to an enriched diet. To determine whether D.noxia feeding damage results in higher concentrations of essential amino acids, stylet exudates were analyzed from wheat (Triticum aestivum) damaged to different degrees. Comparison of samples from undamaged and damaged susceptible wheat revealed changes in amino acid composition and an increase in levels of essential amino acids, indicating a nutritionally enhanced ingesta. The changes in stylet exudates paralleled changes in leaf exudates, indicating that the effects are systemic.Feeding damage is not observed on a resistant wheat host, var. Halt, and leaf exudates from infested Halt did not show changes in amino acid composition.Mean relative growth of nymphs was significantly lower on Halt than on susceptible Arapahoe, indicating that Halt is a less suitable host.Both varieties show similar amino acid levels in non-infested samples, suggesting that D.noxia infestation does not enhance the phloem environment in Halt.This study provides evidence that aphid feeding can generate a nutritionally enhanced phloem diet.