The influence of plant defensive chemicals,diet composition,and winter severity on the nutritional condition of a free‐ranging,generalist herbivore

When consuming plants, herbivores must deal with both low nutritional quality from cell wall constituents and potentially toxic plant secondary metabolites, which are often inversely related. Herbivores that consume a highly nutritious, but chemically defended plant, may consume high levels of toxins that require energy for detoxification. Alternatively, herbivores may avoid consuming high levels of toxins by consuming a diverse diet that may be lower in overall nutritional quality. In this study, we assessed the relationship among nutritional restriction, detoxification and diet diversity in a free‐ranging wild herbivore. We collected urine deposited in the snow (hereafter, snow‐urine) and feces by free‐ranging moose Alces americanus, a generalist browser, during winter. We used the ratio of urinary urea nitrogen to creatinine (UN:C), measured in snow‐urine samples, as an indicator of nutritional restriction, and the ratio of glucuronic acid to creatinine (GA:C), as an indicator of investment in detoxification. We used microhistology to determine diet composition from fecal pellets. GA:C and UN:C were positively associated, suggesting that nutritional condition tends to be worse for individuals investing more in detoxification. We found, after accounting for the influence of winter severity, diet diversity and UN:C to be negatively related, suggesting that increasingly diverse diets were associated with improved nutritional condition. Overall, the most important predictor of UN:C was winter severity and proportion of diet comprised of balsam fir Abies balsamea. Physiological indicators of nutritional restriction tended to be worse during severe winters and among individuals that had consumed more balsam fir. These results highlight complex relationships among environmental conditions, foraging decisions, and costs of detoxification that can influence nutritional condition of herbivores.     

Community- Weighted Mean Plant Traits Predict Small Scale Distribution of Insect Root Herbivore Abundance

Small scale distribution of insect root herbivores may promote plant species diversity by creating patches of different herbivore pressure. However, determinants of small scale distribution of insect root herbivores, and impact of land use intensity on their small scale distribution are largely unknown. We sampled insect root herbivores and measured vegetation parameters and soil water content along transects in grasslands of different management intensity in three regions in Germany. We calculated community-weighted mean plant traits to test whether the functional plant community composition determines the small scale distribution of insect root herbivores. To analyze spatial patterns in plant species and trait composition and insect root herbivore abundance we computed Mantel correlograms. Insect root herbivores mainly comprised click beetle (Coleoptera, Elateridae) larvae (43%) in the investigated grasslands. Total insect root herbivore numbers were positively related to community-weighted mean traits indicating high plant growth rates and biomass (specific leaf area, reproductive- and vegetative plant height), and negatively related to plant traits indicating poor tissue quality (leaf C/N ratio). Generalist Elaterid larvae, when analyzed independently, were also positively related to high plant growth rates and furthermore to root dry mass, but were not related to tissue quality. Insect root herbivore numbers were not related to plant cover, plant species richness and soil water content. Plant species composition and to a lesser extent plant trait composition displayed spatial autocorrelation, which was not influenced by land use intensity. Insect root herbivore abundance was not spatially autocorrelated. We conclude that in semi-natural grasslands with a high share of generalist insect root herbivores, insect root herbivores affiliate with large, fast growing plants, presumably because of availability of high quantities of food. Affiliation of insect root herbivores with large, fast growing plants may counteract dominance of those species, thus promoting plant diversity.     

Lianas as a food resource for herbivorous insects: a comparison with trees

Woody climbers or, ‘lianas’, are one of the features that characterise rainforests. They contribute substantially to plant diversity and leaf biomass which makes them a potentially important food source for herbivores. Here, we focus on insect herbivores, folivores in particular, to show how disparities in the quantitative and qualitative availability of leaves between lianas and trees may differentially influence insect folivory and the herbivore communities themselves. We develop a conceptual model and show that lianas in general have lower structural and chemical defences, a greater nutritional profile and a preferable phenology in comparison with trees, which, contrary to our expectations, has led to assemblages of more‐specialised insects. The impacts this has on higher trophic levels and broader ecological networks, however, are poorly known. We show through a study of four tropical floras from different biogeographic realms that lianas are likely to be a target for a wide range of insect herbivore taxa as they are a phylogenetically diverse group and increase diversity of higher taxa at local scales. This, in combination with their highly palatable leaves, may also make them a suitable temporary food source for insects during times when preferred host plants are scarce. This phenomenon has been observed in mammalian herbivores but awaits investigation in insects as does the effects this may have on survival and fitness. Apparent recent increases in liana abundances in some forests, likely due to climate change, makes understanding their role in supporting and maintaining biodiversity an increasingly important and necessary challenge. Since trees or saplings have usually been the subject of studies on insect herbivory, major knowledge gaps remain about the ways in which lianas contribute to, support and maintain the ecosystems in which they exist. We use our conceptual model to guide future research directions and express the necessity for caution when extrapolating explanations of herbivory derived from data on trees to growth forms with fundamentally different ecologies.     

Trophic Interactions during Primary Succession: Herbivores Slow a Plant Reinvasion at Mount St. Helens

Lupines (Lupinus lepidus var. lobbii), the earliest plant colonists of primary successional habitats at Mount St. Helens, were expected to strongly affect successional trajectories through facilitative effects. However, their effects remain localized because initially high rates of reinvasive spread were short lived, despite widespread habitat availability. We experimentally tested whether insect herbivores, by reducing plant growth and fecundity at the edge of the expanding lupine population, could curtail the rate of reinvasion and whether those herbivores had comparable impacts in the older, more successionally advanced core region. We found that removing insect herbivores increased both the areal growth of individual lupine plants and the production of new plants in the edge region, thereby accelerating the lupine's intrinsic rate of increase at the front of the lupine reinvasion. We found no such impacts of herbivory in the core region, where low plant quality or a complex of recently arrived natural enemies may hold herbivores in check. In the context of invasion theory, herbivore-mediated decreases in lupine population growth rate in the edge region translate into decreased rates of lupine spread, which we quantify here using diffusion models. In the Mount St. Helens system, decreased rate of lupine reinvasion will result in reductions in rates of soil formation, nitrogen input, and entrapment of seeds and detritus that are likely to postpone or alter trajectories of primary succession. If the type of spatial subtleties in herbivore effects we found here are common, with herbivory focused on the edge of an expanding plant population and suppressed or ineffective in the larger, denser central region (where the plants might be more readily noticed and studied), then insect herbivores may have stronger impacts on the dynamics of primary succession and plant invasions than previously recognized.     

Above- and belowground insect herbivores differentially affect soil nematode communities in species-rich plant communities

Interactions between above‐ and belowground invertebrate herbivores alter plant diversity, however, little is known on how these effects may influence higher trophic level organisms belowground. Here we explore whether above‐ and belowground invertebrate herbivores which alter plant community diversity and biomass, in turn affect soil nematode communities. We test the hypotheses that insect herbivores 1) alter soil nematode diversity, 2) stimulate bacterial‐feeding and 3) reduce plant‐feeding nematode abundances. In a full factorial outdoor mesocosm experiment we introduced grasshoppers (aboveground herbivores), wireworms (belowground herbivores) and a diverse soil nematode community to species‐rich model plant communities. After two years, insect herbivore effects on nematode diversity and on abundance of herbivorous, bacterivorous, fungivorous and omni‐carnivorous nematodes were evaluated in relation to plant community composition. Wireworms did not affect nematode diversity despite enhanced plant diversity, while grasshoppers, which did not affect plant diversity, reduced nematode diversity. Although grasshoppers and wireworms caused contrasting shifts in plant species dominance, they did not affect abundances of decomposer nematodes at any trophic level. Primary consumer nematodes were, however, strongly promoted by wireworms, while community root biomass was not altered by the insect herbivores. Overall, interaction effects of wireworms and grasshoppers on the soil nematodes were not observed, and we found no support for bottom‐up control of the nematodes. However, our results show that above‐ and belowground insect herbivores may facilitate root‐feeding rather than decomposer nematodes and that this facilitation appears to be driven by shifts in plant species composition. Moreover, the addition of nematodes strongly suppressed shoot biomass of several forb species and reduced grasshopper abundance. Thus, our results suggest that nematode feedback effects on plant community composition, due to plant and herbivore parasitism, may strongly depend on the presence of insect herbivores.     

Compensation behaviour by insect herbivores and natural enemies: its influence on community structure

Insect herbivores feeding on low-quality plants often compensate by increasing their consumption of plant tissue. This usually results in a longer developmental time leading to a higher vulnerability to natural enemies. This has been termed the slow-growth, high-mortality hypothesis. To explore how compensation may shape the species composition of herbivore and natural enemy populations, we present a mathematical model of a tri-trophic system incorporating both the nutritional quality of plants and herbivores, and the compensatory ability of herbivores and their natural enemies. Using this model we predict the abundance of herbivores and natural enemies, and some characteristics of the composition of species of insect communities along a gradient of plant nutritional quality. Specifically, we make the following predictions: 1) In the absence of natural enemies, the abundance of the juvenile herbivores increases with plant quality, and only highly compensating herbivores persist at low plant nutritional quality. 2) If natural enemies are present, the abundance of the juvenile herbivores decreases with increasing plant quality due to more effective suppression by the natural enemies. Poorly compensating herbivores increase while their highly compensating counterparts decrease with lowered plant quality. 3) When the plants have low nutritional quality, natural enemies will only persist when either very highly compensating herbivores are present or if the natural enemy itself is highly compensating. 4) The abundance of adult herbivores in a community with natural enemies can either increase or decrease with increasing plant quality depending on the compensatory abilities of herbivores and natural enemies.     

Indirect effects of deer on insect pests and soybean plants

1. White-tailed deer (Odocoileus virginianus Zimmermann) and insect pests negatively affect soybean production; however, little is known about how these herbivores potentially interact to affect soybean yield. Previous studies have shown deer browse on non-crop plants affects insect density and insect-mediated leaf damage, which together reduce plant reproductive output. In soybeans, reproductive output is influenced by direct and indirect interactions of different herbivores.
2. Here, we quantified indirect interactions between two groups of herbivores (mammals and insects) and their effects on soybean growth and yield. We examined responses of insect pest communities along a gradient of deer herbivory (29% to 49% browsed stems) in soybean monocultures.
3. Structural equation models showed that deer browse had direct negative effects on soybean plant height and yield. Deer browse indirectly decreased insect-mediated leaf damage by reducing plant height. Deer browse also indirectly increased pest insect abundance through reductions in plant height. Similarly, deer herbivory had an indirect positive effect on leaf carbon: nitrogen ratios through changes in plant height, thereby decreasing leaf nutrition.
4. These results suggest that pest insect abundance may be greater on soybean plants in areas of higher deer browse, but deer browse may reduce insect herbivory through reduced leaf nutrition.

     

Behavioral and morphological responses of an insect herbivore to low nutrient quality are inhibited by plant chemical defenses

Animals have several strategies to contend with nutritionally poor diets, including compensatory consumption and enhanced food utilization efficiencies. Plants produce a diversity of defense compounds that affect the ability of herbivores to utilize these strategies in response to variation in food nutritional quality. Little is known, however, about effects of allelochemicals on herbivores utilizing integrated behavioral and morphological responses to reduced food quality. Our objectives were to (1) examine how variation in diet nutritional quality influences compensatory responses of a generalist insect herbivore, and (2) determine how plant defenses affect these processes. Gypsy moth (Lymantria dispar) larvae were administered one of nine combinations of diet having low, moderate, or high nutritional quality and 0, 2, or 4 % purified aspen (Populus tremuloides) salicinoids. We quantified larval growth, consumption, frass production, and biomass allocation to midgut tissue over a 4-day bioassay. In the absence of salicinoids, larvae compensated for reduced nutritional quality and maintained similar growth across all diets through increased consumption, altered midgut biomass allocation, and improved processing efficiencies. Dietary salicinoids reduced larval consumption, midgut biomass allocation, digestive efficiencies, and growth at all nutritional levels, but the effect size was more pronounced when larvae were fed nutritionally suboptimal diets. Our findings demonstrate that integrated behavioral and morphological compensatory responses to reduced food quality are affected by plant defenses, ultimately limiting compensatory responses and reducing larval performance.     

Plant traits shape soil legacy effects on individual plant–insect interactions

Plant-mediated soil legacy effects can be important determinants of the performance of plants and their aboveground insect herbivores, but, soil legacy effects on plant–insect interactions have been tested for only a limited number of host plant species and soils. Here, we tested the performance of a polyphagous aboveground herbivore, caterpillars of the cabbage moth Mamestra brassicae, on twelve host plant species that were grown on a set of soils conditioned by each of these twelve species. We tested how growth rate (fast- or slow-growing) and functional type (grass or forb) of the plant species that conditioned the soil and of the responding host plant species growing in those soils affect the response of insect herbivores to conditioned soils. Our results show that plants and insect herbivores had lower biomass in soils that were conditioned by fast-growing forbs than in soils conditioned by slow-growing forbs. In soils conditioned by grasses, growth rate of the conditioning plant had the opposite effect, i.e. plants and herbivores had higher biomass in soils conditioned by fast-growing grasses, than in soils conditioned by slow-growing grasses. We show that the response of aboveground insects to soil legacy effects is strongly positively correlated with the response of the host plant species, indicating that plant vigour may explain these relationships. We provide evidence that soil communities can play an important role in shaping plant–insect interactions aboveground. Our results further emphasize the important and interactive role of the conditioning and the response plant in mediating soil–plant–insect interactions.     

Vitamin C content in plants is modified by insects and influences susceptibility to herbivory

Analysis of a diverse cross‐sample of plant‐insect interactions suggests that the abundance of vitamin C (L ‐ascorbic acid, ascorbate or AsA) in plants influences their susceptibility to insect feeding. These effects may be mediated by AsAs roles as an essential dietary nutrient, as an antioxidant in the insect midgut, or as a substrate for plant‐derived ascorbate oxidase, which can lead to generation of toxic reactive oxygen species. Ascorbate can also influence the efficacy of plant defenses such as myrosinases and tannins, and alter insects' susceptibility to natural enemies. Conversely, herbivores appear to influence both de novo synthesis and redox cycling of AsA in their host plants, thereby potentially altering the nutritional value of crops and their susceptibility to pests. The recent development of genetically modified crops with enhanced AsA content provides both an impetus and a tool set for further studies on the role of AsA in plant‐insect interactions.     

How do host plant use and seasonal life cycle relate to insect body size: A case study on European geometrid moths (Lepidoptera: Geometridae)

We used European geometrid moths (>630 species) as a model group to investigate how life history traits linked to larval host plant use (i.e., diet breadth and host-plant growth form) and seasonal life cycle (i.e., voltinism, overwintering stage and caterpillar phenology) are related to adult body size in holometabolous insect herbivores. To do so, we applied phylogenetic comparative methods to account for shared evolutionary history among herbivore species. We further categorized larval diet breadth based on the phylogenetic structure of utilized host plant genera. Our results indicate that species associated with woody plants are, on average, larger than herb feeders and increase in size with increasing diet breadth. Obligatorily univoltine species are larger than multivoltine species, and attain larger sizes when their larvae occur exclusively in the early season. Furthermore, the adult body size is significantly smaller in species that overwinter in the pupal stage compared to those that overwinter as eggs or caterpillars. In summary, our results indicate that the ecological niche of holometabolous insect herbivores is strongly interrelated with body size at maturity.     

Plant-mediated effects in the Brassicaceae on the performance and behaviour of parasitoids

Direct and indirect plant defences are well studied, particularly in the Brassicaceae. Glucosinolates (GS) are secondary plant compounds characteristic in this plant family. They play an important role in defence against herbivores and pathogens. Insect herbivores that are specialists on brassicaceous plant species have evolved adaptations to excrete or detoxify GS. Other insect herbivores may even sequester GS and employ them as defence against their own antagonists, such as predators. Moreover, high levels of GS in the food plants of non-sequestering herbivores can negatively affect the growth and survival of their parasitoids. In addition to allelochemicals, plants produce volatile chemicals when damaged by herbivores. These herbivore induced plant volatiles (HIPV) have been demonstrated to play an important role in foraging behaviour of insect parasitoids. In addition, biosynthetic pathways involved in the production of HIPV are being unraveled using the model plant Arabidopsis thialiana. However, the majority of studies investigating the attractiveness of HIPV to parasitoids are based on experiments mainly using crop plant species in which defence traits may have changed through artificial selection. Field studies with both cultivated and wild crucifers, the latter in which defence traits are intact, are necessary to reveal the relative importance of direct and indirect plant defence strategies on parasitoid and plant fitness. Future research should also consider the potential conflict between direct and indirect plant defences when studying the evolution of plant defences against insect herbivory.     

Neutral indirect effects of mycorrhizal fungi on a specialist insect herbivore

Arbuscular mycorrhizal (AM) fungi can indirectly affect insect herbivore performance by altering traits in their host plant. Typically, generalist herbivores are negatively affected by AM fungi, whereas specialists are positively affected. This is thought to be caused by differential abilities of specialists and generalists to tolerate and/or exploit plant secondary compounds, the prevalence of which may be related to mycorrhizal colonization. We performed a feeding experiment in which specialist sunflower beetle larvae (Zygogramma exclamationis Fabricius, Chrysomelidae) were fed on mycorrhizal or nonmycorrhizal common annual sunflower plants (Helianthus annuus L., Asteraceae). To determine the indirect effects of AM fungi on the sunflower beetle larvae, we measured insect survival and relative growth rate. We also measured leaf area eaten, which allowed relative growth rate to be broken down into two components: relative consumption rate and efficiency of conversion of ingested food. Contrary to several previous studies, we detected no indirect effects of mycorrhizal fungi on larval survival or on relative growth rate or its components. Small effect sizes suggest that this is nonsignificant biologically, as well as statistically, rather than merely an issue of statistical power. Our results support an emerging view that indirect effects of mycorrhizal fungi on insect herbivores may be complex and idiosyncratic. We suggest that future research should emphasize the effects of mycorrhizal fungi on individual plant traits and how these interact to affect insect performance.     

Plant and insect cuticular lipids serve as behavioral cues for insects

The roles of plant and insect cuticular lipids in insect and plant interactions are reviewed. Emphasis is given to the influence that the host plant and the surface lipids of the host plant have upon insect herbivores and the predators and parasitoids of these herbivores. Variations in cuticular lipids of herbivorous insects are dependent upon the host plant, and these variations may affect the behavior of predators and parasitoids. The cuticular lipids of species which interact on multiple trophic levels are compared. Similarities were found between the hydrocarbons of herbivorous insects, their host plants, and their predators or parasitoids.     

Tolerance to herbivory, and not resistance, may explain differential success of invasive, naturalized, and native North American temperate vines

Numerous hypotheses suggest that natural enemies can influence the dynamics of biological invasions. Here, we use a group of 12 related native, invasive, and naturalized vines to test the relative importance of resistance and tolerance to herbivory in promoting biological invasions. In a field experiment in Long Island, New York, we excluded mammal and insect herbivores and examined plant growth and foliar damage over two growing seasons. This novel approach allowed us to compare the relative damage from mammal and insect herbivores and whether damage rates were related to invasion. In a greenhouse experiment, we simulated herbivory through clipping and measured growth response. After two seasons of excluding herbivores, there was no difference in relative growth rates among invasive, naturalized, and native woody vines, and all vines were susceptible to damage from mammal and insect herbivores. Thus, differential attack by herbivores and plant resistance to herbivory did not explain invasion success of these species. In the field, where damage rates were high, none of the vines were able to fully compensate for damage from mammals. However, in the greenhouse, we found that invasive vines were more tolerant of simulated herbivory than native and naturalized relatives. Our results indicate that invasive vines are not escaping herbivory in the novel range, rather they are persisting despite high rates of herbivore damage in the field. While most studies of invasive plants and natural enemies have focused on resistance, this work suggests that tolerance may also play a large role in facilitating invasions.     

Mammalian Herbivores Alter the Population Growth and Spatial Establishment of an Early-Establishing Grassland Species

Plant-herbivore interactions influence the establishment context of plant species, as herbivores alter the community context in which individual species establish, and the spatial relationship between individuals and their source population as plants invade. This relationship can be described using an establishment kernel, which takes into account movement through seed dispersal, and subsequent establishment of adults. Mammalian herbivores are hypothesized to influence plant population growth and establishment through a combination of consumption of seeds and seedlings, and movement of seeds. While the movement abilities of plants are well known, we have very few empirical mechanistic tests of how biotic factors like mammalian herbivores influence this spread potential. As herbivores of all sizes are abundant on the landscape, we asked the question, how do mammalian herbivores influence the population growth, spatial establishment, and the community establishment context of an early-recruiting native prairie legume, Chamaecrista fasciculata? We planted C. fasciculata in source populations within a four-acre tallgrass prairie restoration in plots with and without herbivores, and monitored its establishment with respect to distance from the source populations. We found that herbivores decreased population growth, and decreased the mean and range establishment distance. Additionally, C. fasciculata established more often without herbivores, and when surrounded by weedy, annual species. Our results provide insight into how the interactions between plants and herbivores can alter the spatial dynamics of developing plant communities, which is vital for colonization and range spread with fragmentation and climate change. Mammalian herbivores have the potential to both slow rates of establishment, but also determine the types of plant communities that surround invading species. Therefore, it is essential to consider the herbivore community when attempting to restore functioning plant communities.     

Metabolism of poplar salicinoids by the generalist herbivore Lymantria dispar (Lepidoptera)

The survival of insect herbivores on chemically defended plants may often depend on their ability to metabolize these defense compounds. However, only little knowledge is available on how insects actually process most plant defense compounds. We investigated the metabolism of salicinoids, a major group of phenolic glycosides in poplar and willow species, by a generalist herbivore, the gypsy moth (Lymantria dispar). Seven salicinoid metabolites identified in gypsy moth caterpillar feces were mostly conjugates with glucose, cysteine or glycine. Two of the glucosides were phosphorylated, a feature not previously reported for insect metabolites of plant defense compounds. The origins of these metabolites were traced to specific moieties of three major poplar salicinoids ingested, salicin, salicortin and tremulacin. Based on the observed metabolite patterns we were able to deduce the initial steps of salicinoid breakdown in L. dispar guts, which involves cleavage of ester bonds. The conjugated molecules were effectively eliminated within 24 h after ingestion. Some of the initial breakdown products (salicin and catechol) demonstrated negative effects on insect growth and survival in bioassays on artificial diets. Gypsy moth caterpillars with prior feeding experience on salicinoid-containing poplar foliage converted salicinoids to the identified metabolites more efficiently than caterpillars pre-fed an artificial diet. The majority of the metabolites we identified were also produced by other common poplar-feeding insects. The conversion of plant defenses like salicinoids to a variety of water-soluble sugar, phosphate and amino acid conjugates and their subsequent excretion fits the general detoxification strategy found in insect herbivores and other animals.     

The direct and ecological costs of an ant-plant symbiosis

How strong is selection for cheating in mutualisms? The answer depends on the type and magnitude of the costs of the mutualism. Here we investigated the direct and ecological costs of plant defense by ants in the association between Cordia nodosa, a myrmecophytic plant, and Allomerus octoarticulatus, a phytoecious ant. Cordia nodosa trees produce food and housing to reward ants that protect them against herbivores. For nearly 1 year, we manipulated the presence of A. octoarticulatus ants and most insect herbivores on C. nodosa in a full-factorial experiment. Ants increased plant growth when herbivores were present but decreased plant growth when herbivores were absent, indicating that hosting ants can be costly to plants. However, we did not detect a cost to ant colonies of defending host plants against herbivores. Although this asymmetry in costs suggests that the plants may be under stronger selection than the ants to cheat by withholding investment in their partner, the costs to C. nodosa are probably at least partly ecological, arising because ants tend scale insects on their host plants. We argue that ecological costs should favor resistance or traits other than cheating and thus that neither partner may face much temptation to cheat.     

Induced defences in the neotropical tree Bauhinia brevipes (Vog.) to herbivory: effects of damage-induced changes on leaf quality and insect attack

Induced defences to herbivory are physical, nutritional, and allelochemical traits that change in plants following damage or stress, and that reduce the performance and/or preference of herbivores. The aim of this study was to verify the occurrence and effect of induced responses in Bauhinia brevipes (Vog.) (Leguminosae) which defend it against herbivores, through the manipulation of its leaves, and their effects on herbivore foraging behaviour. We selected 15 plants in the field, and three shoots per plant were subjected to one of three treatments: (1) damaged shoots (simulation of the main types of foliar herbivory and insect exclusion); (2) damaged control shoots (insect exclusion); and (3) control shoots (not manipulated). Water and nitrogen content, tannin concentration, levels of herbivory, and shoot growth rates were compared among treatments. Leaf quality varied among treatments. Damaged leaves showed higher tannin concentration, and lower water and nitrogen content compared to undamaged leaves. On the other hand, they experienced higher rates of herbivory than leaves on control shoots. Moreover, shoots that were experimentally induced showed a higher increase in final shoot length. These results suggest that simulated herbivory on B. brevipes reduced the nutritional quality of its leaves and increased the amount of secondary compounds, therefore altering insect herbivore attack and increasing shoot performance.