Response of five insect herbivores to multiple allelochemicals under fluctuating temperatures

Analysis of the combined effects of allelochemicals on insect herbivores is useful because there may be adverse additive or even synergistic effects. Analysis of the simultaneous effects of temperature and alleochemicals is also necessary because these factors may interact. We examined the effects of three allelochemicals found in tomato (chlorogenic acid, rutin and tomatine) and thermal regime (21:10 °C and 26:15 °C, representing spring and summer respectively) on five insect herbivores (a Solanaceae specialist, Manduca sexta, and the polyphagous Heliothis virescens, Pseudoplusia includens, Spodoptera frugiperda and Trichoplusia ni). There were allelochemical interactions and thermal regime-allelochemical interactions for all species, and so the patterns were complex. In some cases, paired allelochemicals or the combination of three allelochemicals showed adverse additive effects on insect performance. But that was not always the case, and there were only a few examples of synergism. Negative effects of the allelochemicals were sometimes, but not always, damped by the cooler thermal regime. Comparing the growth rates of the five species in this study with those of a previous study (a total of seven species) revealed five patterns. For two of three pairs of closely-related species, the paired species had distinctly different patterns. For example, for H. virescens, tomatine prevented development and chlorogenic acid slowed growth, whereas for Helicoverpa zea, tomatine just slowed growth and the phenolics had little effect. The specialist Manduca sexta had a pattern that was midway between patterns of the generalists; it was not the most tolerant of the allelochemicals.     

Comparative analysis of quantitative trait loci controlling glucosinolates,myrosinase and insect resistance in Arabidopsis thaliana

Evolutionary interactions among insect herbivores and plant chemical defenses have generated systems where plant compounds have opposing fitness consequences for host plants, depending on attack by various insect herbivores. This interplay complicates understanding of fitness costs and benefits of plant chemical defenses. We are studying the role of the glucosinolate-myrosinase chemical defense system in protecting Arabidopsis thaliana from specialist and generalist insect herbivory. We used two Arabidopsis recombinant inbred populations in which we had previously mapped QTL controlling variation in the glucosinolate-myrosinase system. In this study we mapped QTL controlling resistance to specialist (Plutella xylostella) and generalist (Trichoplusia ni) herbivores. We identified a number of QTL that are specific to one herbivore or the other, as well as a single QTL that controls resistance to both insects. Comparison of QTL for herbivory, glucosinolates, and myrosinase showed that T. ni herbivory is strongly deterred by higher glucosinolate levels, faster breakdown rates, and specific chemical structures. In contrast, P. xylostella herbivory is uncorrelated with variation in the glucosinolate-myrosinase system. This agrees with evolutionary theory stating that specialist insects may overcome host plant chemical defenses, whereas generalists will be sensitive to these same defenses.     

Specialization pays off: contrasting effects of two types of tannins on oak specialist and generalist moth species

Phytochemical coevolution theory posits that specialist herbivores will be less sensitive than generalists to the defensive compounds of their host. On the other hand, both types of herbivores should allegedly be similarly sensitive to ‘quantitative’ defences, such as tannin compounds. In this paper, we critically examine the biological effects of two types of tannins: vescalagin (a quantitatively dominant hydrolysable tannin of Quercus robur), and a mix of condensed tannins. In a phylogenetically controlled design, we compare the response of two specialist moth species (Dichonia aprilina and Catocala sponsa) and two generalist species (Acronicta psi and Amphipyra pyramidea) to four artificial diets: a control diet, a diet with 50 mg g^?1 vescalagin, a diet with 15 mg/g condensed tannins, and a diet with both 50 mg g^?1 vescalagin and 15 mg g^?1 condensed tannins. Overall, we find drastic effects of vescalagin and pronounced differences in the responses of generalist and specialist herbivores, but no detectable effects of condensed tannins, and no interaction between the two types of compounds. More specifically, vescalagin reduced the growth of generalist species to one‐half of control levels over 72 h. The compound served as a strong feeding deterrent to generalists, reducing ingestion rates by two‐thirds. Vescalagin also reduced the metabolic and growth efficiency of generalist species to between 16% and 56% of control levels – effects which were lacking or even reversed in specialist species. These patterns suggest that vescalagin forms an important part of the oak's defence against herbivores, and that specialist species have adapted to deal with such substances. In terms of biological effects, condensed tannins seem much less important. Given a quantitative dominance of hydrolysable tannins over condensed tannins in oak leaves, and a seasonal decline in overall tannin levels, these findings contradict the previous notion that widespread spring feeding among oak herbivores could be attributed to tannins.     

Attract and deter: a dual role for pyrrolizidine alkaloids in plant–insect interactions

Pyrrolizidine alkaloids (PAs) are the major defense compounds of plants in the Senecio genus. Here I will review the effects of PAs in Senecio on the preference and performance of specialist and generalist insect herbivores. Specialist herbivores have evolved adaptation to PAs in their host plant. They can use the alkaloids as cue to find their host plant and often they sequester PAs for their own defense against predators. Generalists, on the other hand, can be deterred by PAs. PAs can also affect survival of generalist herbivores. Usually generalist insects avoid feeding on young Senecio leaves, which contain a high concentration of alkaloids. Structurally related PAs can differ in their effects on insect herbivores, some are more toxic than others. The differences in effects of PAs on specialist and generalists could lead to opposing selection on PAs, which may maintain the genetic diversity in PA concentration and composition in Senecio species.     

Specificity of induced resistance in wild radish: causes and consequences for two specialist and two generalist caterpillars

Inducible plant resistance against herbivores is becoming a paradigm of plant–herbivore ecology. Fundamental to understanding induced resistance and its evolutionary ecology is specificity of "induction" and "effects". Specificity in the induction of resistance refers to whether plant damage by various herbivores causes the same response in plants. Specificity in the effects of induced resistance refers to whether induction has the same consequences (i.e., reduced preference or performance) for various herbivores. I examined both specificity of induction and effect employing four lepidopteran herbivores and wild radish plants, a system for which fitness benefits and costs of induction have been documented for the plant. Variation in the specificity of induction and effects of induced plant resistance was found; however, this variation was not associated with diet specialization in the herbivores (i.e., specialists vs generalists). Induction caused by Plutella (specialist) and Spodoptera (generalist) resulted in general resistance to all of the herbivores, induction caused by Pieris (specialist) induced resistance only to Spodoptera (generalist) and Pieris , and plant damage by Trichoplusia (generalist) failed to induce resistance and reduce the performance of any of the herbivores. To the contrary, plants damaged by Trichoplusia supported enhanced growth of subsequently feeding Trichoplusia compared to uninduced controls. These results add a novel level of complexity to interactions between plants and leaf chewing caterpillars. Within the same guild of feeders, some herbivores cause strong induced resistance, no induced resistance, or induced susceptibility. Similarly, caterpillar species were variable in the level to which induced resistance affected their performance. Such interactions limit the possibility of pairwise coevolution between plants and herbivores, and suggest that coevolution can only be diffuse.     

Specificity of induced plant responses to specialist herbivores of the common milkweed Asclepias syriaca

Induced plant responses to herbivory appear to be universal, yet the degree to which they are specific to sets of herbivores is poorly understood. The generalist/specialist hypothesis predicts that generalist herbivores are more often negatively affected by host plant defenses, wheras specialists may be either unaffected by or attracted to these same "plant defenses". Therefore, specialists should be less predictable than generalists in their responses to induced plant resistance traits. To better understand the variation in plant responses to herbivore attack, and the impacts these responses have on specialist herbivores, we conducted a series of experiments examining pairwise interactinos between two specialaist herbivores of the common milkweed ( Asclepias syriaca ). We damaged plants mechnically, with swamp milkweed beetles ( Labidomera clivicollis ), or with monarchs ( Danaus plexippus ), and then asessed specificity of elicitation, both by measuring a putative defensive trait (latex volume) and by challenging plants with insects of both species in bioasays. Latex production increased by 34% and 13% following beetle and monarch herbivory, respectively, but only beetles significantly elevated latex production compared to undamaged controls. While beetle growth was negatively affected by latex across all experiments, beetles were not affected by previous damage caused by conspecifies or by monarchs. In contrast, monarchs feeding on previously damaged plants were 20% smaller, and their response was the same on plants damaged mechnically or by either herbivore. Therefore, these specialist herbivores exhibit both specificity of elicitation in plant responses and specificity of effects in response to prior damage.     

Experimental demography and the vital rates of generalist and specialist insect herbivores on native and novel host plants

1. Colonization success of species when confronted with novel environments is of interest in ecological, evolutionary and conservation contexts. Such events may represent the first step for ecological diversification. They also play an important role in adaptive divergence and speciation. 2. A species that is able to do well across a range of environments has a higher plasticity than one whose success is restricted to a single or few environments. The breadth of environments in which a species can succeed is ultimately determined by the full pattern of its vital rates in each environment. 3. Examples of organisms colonizing novel environments are insect herbivores expanding their diets to novel host plants. One expectation for insect herbivores is that species with specialized diets may display less plasticity when faced with novel hosts than generalist species. 4. We examine this hypothesis for two generalist and two specialist neotropical beetles (genus Cephaloleia: Chrysomelidae) currently expanding their diets from native to novel plants of the order Zingiberales. Using an experimental approach, we estimated changes in vital rates, life-history traits and lifetime fitness for each beetle species when feeding on native or novel host plants. 5. We did not find evidence supporting more plasticity for generalists than for specialists. Instead, we found similar patterns of survival and fecundity for all herbivores. Larvae survived worse on novel hosts; adults survived at least as well or better, but reproduced less on the novel host than on natives. 6. Some of the novel host plants represent challenging environments where population growth was negative. However, in four novel plant-herbivore interactions, instantaneous population growth rates were positive. 7. Positive instantaneous population growth rates during initial colonization of novel host plants suggest that both generalist and specialist Cephaloleia beetles may be pre-adapted to feed on some novel hosts. This plasticity in host use is a key factor for successful colonization of novel hosts. Future success or failure in the colonization of these novel hosts will depend on the demographic rates described in this research, natural selection and the evolutionary responses of life-history traits in novel environments.     

Effects of chlorogenic acid- and tomatine-fed caterpillars on performance of an insect predator

Two diet experiments addressed the effects of allelochemical-fed prey (Manduca sexta caterpillars), temperature, and gender on performance of the insect predator, Podisus maculiventris. Two of the major allelochemicals in tomato were used: chlorogenic acid and tomatine. Predator performance was negatively affected by both chlorogenic acid-fed and tomatine fed-prey, and there were allelochemical by thermal regime interactions for both. Relative consumption rate and growth rate decreased at the higher levels of tomatine at the warmer thermal regime (summer conditions) but were unaffected at the cooler thermal regime (spring conditions). At the cooler thermal regime, stadium duration was prolonged when the predators were given chlorogenic acid-fed prey, but at the warmer thermal regime there was no such effect. There were several effects of gender: biomass gained, food consumed, relative growth rate and efficiency of conversion of ingested food to biomass were higher for females than males. Furthermore, the effects of thermal regime and tomatine on food consumption and biomass gained differed for females and males. In general, the hypothesis that generalist insect predators may be a selective pressure shaping host plant range of insect herbivores was supported by these results. But the occurrence of allelochemical by thermal regime interactions means that it will be difficult to determine the relative importance of plant chemistry versus predators on patterns of feeding specialization by herbivores without taking into account a third factor, temperature. Received: 20 March 1995 /Accepted: 2 August 1996     

Invertebrate herbivory along a gradient of plant species diversity in extensively managed grasslands

Increasing plant diversity has long been hypothesized to negatively affect levels of invertebrate herbivory due to a lower number of specialist insect herbivores in more diverse sites, but studies of natural systems have been rare. We used a planned comparison to study herbivory in a set of 19 semi-natural montane grasslands managed as hay meadows. Herbivory was measured in transects through the plant communities, and in individuals of Plantago lanceolata and Trifolium pratense that were transplanted into each meadow. In addition, plant community biomass and arthropod abundances were determined in the grasslands. Before the first mowing in June, mean herbivory levels correlated negatively with plant species richness, as predicted by theory, but they were also significantly affected by plant community biomass and plant community composition. After mowing, herbivory levels were only significantly related to plant community composition. Damage levels in the transplants were lower than herbivory levels in the established plant communities. Most insect herbivores were generalists and not specialists. The number of insect herbivores and spiders were positively correlated and tended to increase with increasing plant species richness. Herbivory levels were correlated negatively with spider abundances. We conclude that while the predicted negative relationship between plant species richness and insect herbivory can be found in grasslands, the underlying mechanism involves generalist rather than specialist herbivores. Our data also suggest a role of natural enemies in generalist herbivore activities.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Diversity and abundance of insect herbivores foraging on seedlings in a rainforest in Guyana

1. Free-living insect herbivores foraging on 10 000 tagged seedlings representing five species of common rainforest trees were surveyed monthly for more than 1 year in an unlogged forest plot of 1 km² in Guyana. 2. Overall, 9056 insect specimens were collected. Most were sap-sucking insects, which represented at least 244 species belonging to 25 families. Leaf-chewing insects included at least 101 species belonging to 16 families. Herbivore densities were among the lowest densities reported in tropical rainforests to date: 2.4 individuals per square metre of foliage. 3. Insect host specificity was assessed by calculating Lloyd’s index of patchiness from distributional records and considering feeding records in captivity and in situ. Generalists represented 84 and 78% of sap-sucking species and individuals, and 75 and 42% of leaf-chewing species and individuals. In particular, several species of polyphagous xylem-feeding Cicadellinae were strikingly abundant on all hosts. 4. The high incidence of generalist insects suggests that the Janzen–Connell model, explaining rates of attack on seedlings as a density-dependent process resulting from contagion of specialist insects from parent trees, is unlikely to be valid in this study system. 5. Given the rarity of flushing events for the seedlings during the study period, the low insect densities, and the high proportion of generalists, the data also suggest that seedlings may represent a poor resource for free-living insect herbivores in rainforests.     

Specialist and generalist herbivores exert opposing selection on a chemical defense

* Plant defense traits often show high levels of genetic variation, despite clear impacts on plant fitness. This variation may be partly maintained by trade-offs in the defense against multiple herbivore species, for example between generalists and coevolved specialists. Despite a long-standing discussion in the literature on the subject, no study to date has specifically manipulated specialist and generalist herbivores independently of one another to determine whether the two guilds exert opposing selection pressures on specific defensive traits. * In two separate experiments, the dominant specialist and generalist herbivores of Brassica nigra were independently manipulated to test whether the composition of the herbivore community altered the direction of selection on a major defensive trait of the plant, sinigrin concentration. * It was found that generalist damage was negatively correlated but specialist loads were positively correlated with increasing sinigrin concentrations; and sinigrin concentration was favored when specialists were removed, disfavored (past an intermediate point) when generalists were removed and selectively neutral when plants faced both generalists and specialists.     

Insect herbivore counteradaptations to the plant glucosinolate-myrosinase system

The glucosinolate-myrosinase system found in plants of the Brassicales order is one of the best studied plant chemical defenses. Glucosinolates and their hydrolytic enzymes, myrosinases, are stored in separate compartments in the intact plant tissue. Upon tissue disruption, bioactivation of glucosinolates is initiated, i.e. myrosinases get access to their glucosinolate substrates, and glucosinolate hydrolysis results in the formation of toxic isothiocyanates and other biologically active products. The defensive function of the glucosinolate-myrosinase system has been demonstrated in a variety of studies with different insect herbivores. However, a number of generalist as well as specialist herbivores uses glucosinolate-containing plants as hosts causing large agronomical losses in oil seed rape and other crops of the Brassicaceae. While our knowledge of counteradaptations in generalist insect herbivores is still very limited, considerable progress has been made in understanding how specialist insect herbivores overcome the glucosinolate-myrosinase system and even exploit it for their own defense. All mechanisms of counteradaptation identified to date in insect herbivores specialized on glucosinolate-containing plants ensure that glucosinolate breakdown to toxic isothiocyanates is avoided. This is accomplished in many different ways including avoidance of cell disruption, rapid absorption of intact glucosinolates, rapid metabolic conversion of glucosinolates to harmless compounds that are not substrates for myrosinases, and diversion of plant myrosinase-catalyzed glucosinolate hydrolysis. One of these counteradaptations, the nitrile-specifier protein identified in Pierid species, has been used to demonstrate mechanisms of coevolution of plants and their insect herbivores.     

Phytochemical diversity and synergistic effects on herbivores

Synergistic effects of multiple plant secondary metabolites on upper trophic levels constitute an underexplored but potentially widespread component of coevolution and ecological interactions. Examples of plant secondary metabolites acting synergistically as insect deterrents are not common, and many studies focus on the pharmaceutical applications of natural products, where activity is serendipitous and not an evolved response. This review summarizes some systems that are ideal for testing synergistic plant defenses and utilizes a focused meta-analysis to examine studies that have tested effects of multiple compounds on insects. Due to a dearth of ecological synergy studies, one of the few patterns for synergy that we are able to report from the meta-analysis is that phytochemical mixtures have a larger overall effect on generalist herbivores than specialist herbivores. We recommend a focus on synergy in chemical ecology programs and suggest future hypothesis tests and methods. These approaches are not focused on techniques in molecular biology to examine mechanisms at the cellular level, rather we recommend uncovering the existence of synergy first, by combining the best methods in organic synthesis, isolation, chemical ecology, bioassays, and quantitative analyses. Data generated by our recommended methods should provide rigorous tests of important hypotheses on how intraclass and interclass compounds act synergistically to deter insects, disrupt the immune response, and ultimately contribute to diversification. Further synergy research should also contribute to determining if antiherbivore synergy is widespread among plant secondary metabolites, which would be consistent with the hypothesis that synergistic defenses are a key attribute of the evolved diverse chemical mixtures found in plants.     

Combined effects of allelochemical-fed and scarce prey on the generalist insect predator Podisusmaculiventris

1. The simultaneous effects of allelochemicals ingested by herbivorous insect prey and prey scarcity on the performance of a generalist insect predator were examined.
2. Fifth-instar predatory stinkbugs ( Podisus maculiventris : Pentatomidae) were fed caterpillars ( Manduca sexta : Sphingidae) in three prey scarcity treatments: every day (unlimited amount), one caterpillar every third day, one caterpillar every fifth day. The caterpillars were fed either a plain diet or a diet containing rutin, chlorogenic acid and tomatine, which are three of the major allelochemicals in tomato leaves ( Lycopersicon esculentum : Solanaceae), the preferred food of these caterpillars.
3. Food consumed, efficiency of conversion of ingested food to biomass (ECI), biomass gained, stadium duration and relative growth rate (RGR) of predators were negatively affected by prey scarcity. The allelochemicals negatively affected food consumed and ECI.
4. There were prey scarcity by allelochemical interactions for ECI, biomass gained and RGR. For ECI, the allelochemicals had a greater negative impact on the predatory stinkbugs when prey were scarce. When prey diet contained allelochemicals, biomass gained and RGR declined more steeply with increased prey scarcity. There was an allelochemical by predator gender interaction for biomass gained. Allelochemicals had no effect on biomass gained by female stinkbugs, whereas biomass gained declined more steeply with increased prey scarcity for male stinkbugs fed caterpillars containing allelochemicals than for males fed control caterpillars.     

Herbivore responses to plant secondary compounds: a test of phytochemical coevolution theory

Literature data were collected on the floristic distribution and toxicity of phytochemicals to herbivores and on herbivore specialization in order to test phytochemical coevolution theory. The theory makes four predictions that can be tested with this information. Herbivores can adapt to novel, more toxic chemicals by becoming specialists, or they can become generalists but at the cost of lower feeding success on any particular host. Thus, the first two predictions are as follows: herbivores should do better on chemicals that are present in their normal host, and this pattern should be stronger for specialists than for generalists. The "escape and radiation" aspect of the theory holds that if a plant taxon with a novel defense chemical diversifies, the chemical will become widespread. Eventually, herbivores will adapt to and disarm it. So the third prediction is that more widespread chemicals are less toxic than more narrowly distributed ones. Because generalists should not do as well as specialists on chemicals disarmed by the latter, the fourth prediction is that the third prediction should be more true for generalists than specialists and should depend on presence/absence of the chemical in the normal host. Multiple regressions of toxicity (herbivore mortality and final weight) on three predictor variables (chemical presence/absence in the normal host, specialism, and chemical floristic distribution) and relevant interactions were used to test these predictions. Chemical presence/absence in the normal host, the interaction between this variable and specialism, and chemical floristic distribution had significant effects on both measures of toxicity, supporting the first three predictions of the model. Support for the fourth prediction (a three-way interaction among all predictor variables) was evident for final weight but not mortality, perhaps because growth is more responsive to toxicity differences than survival. In short, the phytochemistry literature provides broad support for the phytochemical coevolution model.     

Response of pest control by generalist predators to local‐scale plant diversity: a meta‐analysis

Disentangling the effects of plant diversity on the control of herbivores is important for understanding agricultural sustainability. Recent studies have investigated the relationships between plant diversity and arthropod communities at the landscape scale, but few have done so at the local scale. We conducted a meta‐analysis of 32 papers containing 175 independent measures of the relationship between plant diversity and arthropod communities. We found that generalist predators had a strong positive response to plant diversity, that is, their abundance increased as plant diversity increased. Herbivores, in contrast, had an overall weak and negative response to plant diversity. However, specialist and generalist herbivores differed in their response to plant diversity, that is, the response was negative for specialists and not significant for generalists. While the effects of scale remain unclear, the response to plant diversity tended to increase for specialist herbivores, but decrease for generalist herbivores as the scale increased. There was no clear effect of scale on the response of generalist predators to plant diversity. Our results suggest that the response of herbivores to plant diversity at the local scale is a balance between habitat and trophic effects that vary according to arthropod specialization and habitat type. Synthesis and applications. Positive effects of plant diversity on generalist predators confirm that, at the local scale, plant diversification of agroecosystems is a credible and promising option for increasing pest regulation. Results from our meta‐analysis suggest that natural control in plant‐diversified systems is more likely to occur for specialist than for generalist herbivores. In terms of pest management, our results indicate that small‐scale plant diversification (via the planting of cover crops or intercrops and reduced weed management) is likely to increase the control of specialist herbivores by generalist predators.     

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.     

Preference and performance of generalist and specialist herbivores on chemically defended host plants

1. Both the physiological efficiency (PE) hypothesis and the preference–performance (PP) hypothesis address the complex interactions between herbivores and host plants, albeit from different perspectives. The PE hypothesis contends that specialists are better physiologically adapted to their host plants than generalists. The PP hypothesis predicts that larvae perform best on the host plant preferred by ovipositing females. 2. This study tests components of both hypotheses using the specialist checkerspot, Euphydryas anicia, the generalist salt marsh caterpillar, Estigmene acrea, and host plants in the genus Penstemon, which are defended by iridoid glycosides. 3. In laboratory experiments, the generalist preferred and performed significantly better on the less well defended host plant species. This is consistent with results from a common garden experiment where the less well defended Penstemon species received more damage from the local community of generalists. Larvae of the specialist checkerspot preferred the more chemically defended species in the laboratory, but performed equally well on both hosts. However, field experiments demonstrated that adult checkerspot females preferred to oviposit on the less well defended host plant. 4. Components of the physiological efficiency hypothesis were supported in this system, as the specialist outperformed the generalist on the more iridoid glycoside‐rich host plant species. There was no support for the PP hypothesis, however, as there was no clear relationship between female preference in the field and offspring performance in the laboratory.     

Effects of non-native plants on the native insect community of Delaware

Due to the lack of a co-evolutionary history, the novel defenses presented by introduced plants may be insurmountable to many native insects. Accordingly, non-native plants are expected to support less insect biomass than native plants. Further, native insect specialists may be more affected by introduced plants than native generalist herbivores, resulting in decreased insect diversity on non-native plants due to the loss of specialists. To test these hypotheses, we used a common garden experiment to compare native insect biomass, species richness, and the proportion of native specialist to native generalist insects supported by 45 species of woody plants. Plants were classified into three groupings, with 10 replicates of each species: 15 species native to Delaware (Natives), 15 non-native species that were congeneric with a member of the Native group (Non-native Congeners), and 15 non-native species that did not have a congener present in the United States (Aliens). Native herbivorous insects were sampled in May, June, and July of 2004 and 2005. Overall, insect biomass was greater on Natives than Non-native Congeners and Aliens, but insect biomass varied unpredictably between congeneric pair members. Counter to expectations, Aliens held more insect biomass than did Non-native Congeners. There was no difference in species richness or the number of specialist and generalist species collected among the three plant groupings in either year, although our protocol was biased against sampling specialists. If these results generalize to other studies, loss of native insect biomass due to introduced plants may negatively affect higher trophic levels of the ecosystem.