Caterpillar Herbivory Research Articles

Fatty alcohols, a minor component of the tree tobacco surface wax, are associated with defence against caterpillar herbivory.

Despite decades of research resulting in a comprehensive understanding of epicuticular wax metabolism, the function of these almost ubiquitous metabolites in plant-herbivore interactions remains unresolved. In this study, we examined the effects of CRISPR-induced knockout mutations in four Nicotiana glauca (tree tobacco) wax metabolism genes. These mutations cause a wide range of changes in epicuticular wax composition, leading to altered interactions with insects and snails. Three interaction classes were examined: chewing herbivory by seven caterpillars and one snail species, phloem feeding by Myzus persicae (green peach aphid) and oviposition by Bemisia tabaci (whitefly). Although total wax load and alkane abundance did not affect caterpillar growth, a correlation across species, showed that fatty alcohols, a minor component of N. glauca surface waxes, negatively affected the growth of both a generalist caterpillar (Spodoptera littoralis) and a tobacco-feeding specialist (Manduca sexta). This negative correlation was overshadowed by the stronger effect of anabasine, a nicotine isomer, and was apparent when fatty alcohols were added to an artificial lepidopteran diet. By contrast, snails fed more on waxy leaves. Aphid reproduction and feeding activity were unaffected by wax composition but were potentially affected by altered cutin composition. Wax crystal morphology could explain the preference of B. tabaci to lay eggs on waxy wild-type plants relative to both alkane and fatty alcohol-deficient mutants. Together, our results suggest that the varied responses among herbivore classes and species are likely to be a consequence of the co-evolution that shaped the specific effects of different surface wax components in plant-herbivore interactions.

Predator types, urbanization, and tree cover drive top-down control of herbivorous and carnivorous preys in an urban agroecosystem

ABSTRACT Prey-predator interactions hold significant importance, widely acknowledged as crucial processes within ecosystems. Yet, there is a scarcity of empirical data that effectively illustrates the influence of urbanization on such interactions. We performed a common garden experiment utilizing 1250 clay models to assess the predation risks faced by herbivorous and carnivorous prey in an urban agroecosystem in the southern Philippines. Our findings revealed significant differences in attack risks between the trophic levels, with herbivorous caterpillars (n = 246; 53.25%) experiencing higher predation rates compared to carnivorous lizards (n = 216; 46.75%). Interestingly, while the trophic level of the prey did not directly predict predation risk, the presence of predators showed significant effects. Arthropods emerged as the dominant predators of herbivorous prey compared to other predators, whereas mammalian predators predominantly attacked carnivorous prey. The landscape variable also had a strong influence on the risk of predation. We found that increasing tree cover was significantly related to increased predation risk, while built-up showed the opposite. Our research findings support the ‘increasing disturbance hypothesis’, suggesting that rising urbanization rates reduce predator diversity, resulting in a decrease and loss of predation pressure.

Auditory predator cues decrease herbivore survival and plant damage.

The high fitness cost of predation selects prey capable of detecting risk cues and responding in ways that reduce their vulnerability. While the impacts of auditory predator cues have been extensively researched in vertebrate prey, much less is known about invertebrate species' responses and their potential to affect the wider food web. We exposed larvae of Spodoptera exigua, a slow-moving and vulnerable herbivore hunted by aerial predators, to recordings of wasp buzzing (risk cue), mosquito buzzing (no-risk cue), or a no-sound control in both laboratory and field settings. In the laboratory, wasp buzzing (but not mosquito buzzing) reduced survival relative to the control; there was, however, no effect on time to or weight at pupation in survivors. In the field, wasp buzzing reduced caterpillar herbivory and increased plant biomass relative to the control treatment. In contrast, mosquito buzzing reduced herbivory less than wasp buzzing and had no effect on plant biomass. The fact that wasp cues evoked strong responses in both experiments, while mosquito buzzing generally did not, indicates that caterpillars were responding to predation risk rather than sound per se. Such auditory cues may have an important but largely unappreciated impacts on terrestrial invertebrate herbivores and their host plants.

Cotton plants as ideal models for teaching and research on inducible direct plant defenses

Cotton (Gossypium hirsutum) stores defensive compounds in glands covering its leaves and other tissues. The density and the chemical filling of these glands increase systematically in developing leaves in response to herbivory on older leaves. Cotton seedlings are known to respond more strongly to actual caterpillar herbivory than to mere physical damage. It is not clear whether this amplified response is linked to insect-derived elicitors or difference in damage properties. To investigate this, we assessed the effect of repeated artificial damage without and with application of regurgitant from Spodoptera exigua caterpillars. Repeated mechanical damage led to a systemic increase of gland density, gland size, and content of defensive terpenes, with no detectable additional elicitation upon regurgitant treatment. Dual choice feeding assays further showed that defense induction triggered by just physical damage made newly developing leaves far less palatable to S. exigua larvae as compared to leaves from undamaged seedlings, whereas they did not distinguish between leaves from damaged plants treated with or without regurgitant. Our study confirms that the systemic induction of cotton glands is an unspecific response to physical damage, although cotton is known to respond to caterpillar-associated elicitors for other defensive traits. Cotton glands induction can be readily visualized under modest magnification, making the experiments described in this study highly suited to teach chemical ecology and aspects of plant defense theory in practical classes.

Tree dissimilarity determines multi-dimensional beta-diversity of herbivores and carnivores via bottom-up effects.

Global biodiversity decline and its cascading effects through trophic interactions pose a severe threat to human society. Establishing the impacts of biodiversity decline requires a more thorough understanding of multi-trophic interactions and, more specifically, the effects that loss of diversity in primary producers has on multi-trophic community assembly. Within a synthetic conceptual framework for multi-trophic beta-diversity, we tested a series of hypotheses on neutral and niche-based bottom-up processes in assembling herbivore and carnivore communities in a subtropical forest using linear models, hieratical variance partitioning based on linear mixed-effects models (LMMs) and simulation. We found that the observed taxonomic, phylogenetic and functional beta-diversity of both herbivorous caterpillars and carnivorous spiders were significantly and positively related to tree dissimilarity. Linear models and variance partitioning for LMMs jointly suggested that as a result of bottom-up effects, producer dissimilarities were predominant in structuring consumer dissimilarity, the strength of which highly depended on the trophic dependencies on producers, the diversity facet examined, and data quality. Importantly, linear models for standardized beta-diversities against producer dissimilarities implied a transition between niche-based processes such as environmental filtering and competitive exclusion, which supports the role of bottom-up effect in determining consumer community assembly. These findings enrich our mechanistic understanding of the 'Diversity Begets Diversity' hypothesis and the complexity of higher-trophic community assembly, which is fundamental for sustainable biodiversity conservation and ecosystem management.

Additive genetic effects in interacting species jointly determine the outcome of caterpillar herbivory

Plant-insect interactions are common and important in basic and applied biology. Trait and genetic variation can affect the outcome and evolution of these interactions, but the relative contributions of plant and insect genetic variation and how these interact remain unclear and are rarely subject to assessment in the same experimental context. Here, we address this knowledge gap using a recent host-range expansion onto alfalfa by the Melissa blue butterfly. Common garden rearing experiments and genomic data show that caterpillar performance depends on plant and insect genetic variation, with insect genetics contributing to performance earlier in development and plant genetics later. Our models of performance based on caterpillar genetics retained predictive power when applied to a second common garden. Much of the plant genetic effect could be explained by heritable variation in plant phytochemicals, especially saponins, peptides, and phosphatidyl cholines, providing a possible mechanistic understanding of variation in the species interaction. We find evidence of polygenic, mostly additive effects within and between species, with consistent effects of plant genotype on growth and development across multiple butterfly species. Our results inform theories of plant-insect coevolution and the evolution of diet breadth in herbivorous insects and other host-specific parasites.

The effect of zinc fertilizer on maize growth, leaf mineral nutrition, and caterpillar herbivory

The effect of zinc fertilizer on maize growth, leaf mineral nutrition, and caterpillar herbivory

Contrasting impacts of herbivore induction and elevated atmospheric CO2 on silicon defences and consequences for subsequent herbivores

AbstractPlants are often sequentially attacked by multiple herbivores; feeding by one herbivore can alter host plant quality that affects the performance of subsequent herbivores. Previous studies suggest that silicon (Si) is a highly inducible defence in grasses (Poaceae) following herbivory, so could mediate such temporally separated insect herbivore interactions. Elevated atmospheric CO2 concentrations (eCO2), in contrast, often reduce Si accumulation, which potentially weakens this interaction. We examined the effects of prior feeding by Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on the performance of crickets, Acheta domesticus (L.) (Orthoptera: Gryllidae), subsequently feeding on the same plant. We used Brachypodium distachyon (L.) P. Beauv. grass supplemented or non‐supplemented with Si and grown in the glasshouse maintained at ambient (aCO2) or eCO2 concentrations. As hypothesized, prior feeding by caterpillars induced Si accumulation. Despite eCO2 reducing Si accumulation, initial herbivore induction of Si negated the effects of eCO2. Both, previous caterpillar herbivory and Si supplementation reduced cricket performance. Si induction by successive herbivory was additive. Plant biomass was similar in plants attacked by caterpillars alone or both herbivores, suggesting that initial Si induction by caterpillars deterred feeding by crickets. Our results demonstrate that Si induction by one herbivore negatively impacts successive herbivores, as has been demonstrated for secondary metabolite‐mediated interactions. Uniquely, however, Si induction is an irreversible defence and potentially a stronger, or perhaps longer‐lasting mediator of such herbivore interactions in some plant taxa.

Analysis of Inducible Terpenoids in Cotton Leaves to Test for Indirect Plant–Endophyte-Herbivore Interactions

Analysis of Inducible Terpenoids in Cotton Leaves to Test for Indirect Plant–Endophyte-Herbivore Interactions

Herbivorous Caterpillars and the Green Leaf Volatile (GLV) Quandary.

Several herbivorous caterpillars contain effectors in their oral secretions that alter the emission of green leaf volatiles (GLVs) produced by the plants upon which the caterpillars are feeding. These effectors include an isomerase, a fatty acid dehydratase (FHD), and a heat-stable hexenal trapping (HALT) molecule. GLVs serve as signaling compounds in plant-insect interactions and inter-and intra-plant communication. However, it is not known whether these GLV-altering effectors are common among herbivorous caterpillars, or the evolutionary context of these effectors in relation to GLV emission by host plants in response to feeding damage. Here, we examined the distribution and activity of the isomerase, FHD, and HALT effectors across 10 species spanning 7 lepidopteran families. Six of the 10 species possessed all three effectors in their oral secretions. Activity from the HALT and FHD effectors was observed in all examined caterpillar species, while activity from the isomerase effector varied in some species and was absent in others. There was no discernable pattern in effector activity based on evolutionary divergence, since individual species within a family did not possess similar mechanisms to alter GLV emission. These data, demonstrating the GLV-altering effectors acting at different steps in the GLV biosynthetic pathway and present in the examined caterpillar species at different combinations with different activities, highlight the importance of these effectors in changing the emission of these compounds during caterpillar herbivory. Understanding the prevalence and roles of GLV-altering effectors and GLV emission itself will open new research areas in the dynamics of plant-insect interactions.

Distinct Arabidopsis Responses to Two Generalist Caterpillar Species Differing in Host Breadth

In general, caterpillar herbivores with a narrow host preference (specialists) have evolved mechanisms to circumvent specific plant defenses. In contrast, caterpillars with a broader host range (generalists) may manipulate phytohormone pathways common to many plant species to attenuate induced defenses. Many studies have compared plant responses to specialist versus generalist caterpillars. In contrast, this study evaluates the induced response of Arabidopsis thaliana to two generalist caterpillar species, the cabbage looper, Trichoplusia ni, and the beet armyworm, Spodoptera exigua. Although both caterpillars are considered generalists, S. exigua has a broader plant host range, whereas T. ni prefers Brassicaceous plants. Our study shows that most responses to caterpillar herbivory, such as the jasmonate burst, are similar in plants attacked by either insect species; however, we do observe dynamic and temporal differences in specific responses. Expression of AtZAT10, a 12-oxo-phytodienoic acid-responsive gene, is only induced in response to T. ni damage. In comparison, only S. exigua herbivory activates the salicylic acid/NPR1-dependent pathway, as observed by the expression of the marker gene AtPR1. Even though both species induce AtPDF1.2 expression, we found caterpillar-specific temporal differences: T. ni herbivory results in sustained expression over time, whereas gene expression is sharply downregulated at 36 h in S. exigua-attacked plants. Although damage by these two caterpillar species induced AtMYB28 and AtMYB34 expression, specific short- and long-chain aliphatic and indolic glucosinolates accumulate only in response to S. exigua herbivory. These species-specific, plant-induced responses likely reflect differences in effectors found in caterpillar oral secretions. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Impact of Soil Rhizobacteria Inoculation and Leaf-Chewing Insect Herbivory on Mentha piperita Leaf Secondary Metabolites.

Secondary metabolites commonly play important physiological roles in plants and can be modified quantitatively and qualitatively by exposure to biotic and abiotic interactions. Plant growth promoting rhizobacteria (PGPR) and herbivory induce systemic resistance. In the present study, we analyzed the induction of secondary metabolites in peppermint plants in response to chewing insect herbivory on PGPR-inoculated Mentha piperita plants. The secondary metabolites of M. piperita plants were increased when plants were inoculated with PGPR and also exposed to caterpillar herbivory. It was found that the total essential oil yield in inoculated plants with insect damage was ~2.6-fold higher than in controls. The yield was similar to that of plants either damaged by insects or inoculated, indicating that there was no synergism. The same trend was observed for phenolic compounds. In contrast, VOC emissions were significantly higher in plants infested by insects, independent of whether they were inoculated. Insect damaged plants had 5.5 times higher monoterpene emissions than control plants, and ~ 2-fold higher emissions than on PGPR-inoculated plants without insects. To gain a better understanding of how herbivory on PGPR-inoculated plants can cause an increase in secondary metabolites of peppermint, we examined changes in plant defense hormones in inoculated plants after herbivory. We found that the combination of both treatments increased the endogenous jasmonic and salicylic acid levels to the same extent as in plants only inoculated or only insect-damaged. Because different interactions can alter the phytochemistry of plants such as M. piperita, this topic is both ecologically and economically relevant.

Intraspecific competition reduces plant size and quality and damage severity increases defense responses in the herbaceous perennial, Asclepias syriaca

Competition among plants within populations affects plant size, nutrient status and allocation to defenses. Herbivory places additional stress on plant allocation of resources. When resources are limited due to intraspecific competition, induced defenses may reduce costs of defense responses and trade-offs between allocation to growth or defense. We hypothesized that increased intraspecific competition would result in a decrease in plant size and leaf tissue nutrient quality, and that both intraspecific competition and leaf damage severity would affect inducibility of leaf defensive traits. We tested these hypotheses in common milkweed (Asclepias syriaca) using greenhouse experiments that manipulated plant density and damage severity treatments. We measured a suite of leaf traits generally related with herbivore performance, including size; nitrogen, carbon, lignin, and fiber concentrations; and latex production. Increased density decreased plant size and leaf nutrient quality, but increased lignin levels. Damage severity increased leaf lignin levels and latex production. There were no density–damage severity interactions. We additionally addressed the question of whether plants respond differently to simulated or natural herbivory and hypothesized that insect herbivores and mechanical plant tissue removal would similarly affect induced defensive responses. Leaf fiber and lignin increased in response to damage, but the response was greater on plants subjected to simulated, compared with caterpillar herbivory. Other plant traits responded similarly to either damage type. Our findings suggest that intraspecific competition has the potential to generate feedbacks among plants and herbivores as plants respond to herbivory.

Plant Defense by Latex: Ecological Genetics of Inducibility in the Milkweeds and a General Review of Mechanisms, Evolution, and Implications for Agriculture.

Latex occurs in 10% of plant families, has evolved independently many times, and is the most effective defense of milkweeds against its chewing herbivores. Here we report on new experiments on the heritability and inducibility of latex in several milkweed species. In addition, we review what is known about the genetic and environmental determinants of latex exudation, hormonal regulation, evolution within and among species, and the role and frequency of latex in agricultural crops. We first evaluated genotype-by-environment interactions using ~20 full-sibling genetic families in each of seven Asclepias species treated as controls or attacked by monarch butterfly caterpillars. All species showed substantial genetic variation for latex exudation and six of seven species responded to monarch herbivory (two species increased latex, two species decreased, and two showed variation among genetic families). Exogenous application of jasmonic acid (JA) to three species induced a consistent increase in latex (including species which showed a decline following caterpillar herbivory). We next evaluated three hypotheses for what determines genetic variation for induced latex in A. syriaca: 1) a trade-off with constitutive investment, 2) differential endogenous JA induction, or 3) variation in responsiveness to JA. We only found support for the second hypothesis: genetic families with a stronger JA-burst showed the greatest latex exudation following herbivory. We conclude that most species exhibit a genetic and inducible basis for latex, although genetic variation in inducibility is not pervasive. Finally, we summarized studies across 22 species of Asclepias and found that neither a species' latitude nor its phylogenetic position predicted latex inducibility. Nonetheless, a negative association between constitutive and induced latex across species indicates a macroevolutionary trade-off in allocation to this defense. Our review indicates that jasmonic acid is a key regulator of latex exudation, laticifer morphology, and defensive metabolites within latex. Biotic and abiotic factors strongly modulate latex expression. A survey of latex in food crops revealed that latex and analogous exudates (gums, resins, mucilage) are more common than expected based on their distribution across all plants. In conclusion, despite its widespread occurrence, the literature on latex is currently dominated by rubber trees and milkweeds, and we look forward to the broadening of ecological, agricultural, and mechanistic research into other systems.

Leaf metabolic signatures induced by real and simulated herbivory in black mustard (Brassica nigra)

IntroductionThe oxylipin methyl jasmonate (MeJA) is a plant hormone active in response signalling and defence against herbivores. Although MeJA is applied experimentally to mimic herbivory and induce plant defences, its downstream effects on the plant metabolome are largely uncharacterized, especially in the context of primary growth and tissue-specificity of the response.ObjectivesWe investigated the effects of MeJA-simulated and real caterpillar herbivory on the foliar metabolome of the wild plant Brassica nigra and monitored the herbivore-induced responses in relation to leaf ontogeny.MethodsAs single or multiple herbivory treatments, MeJA- and mock-sprayed plants were consecutively exposed to caterpillars or left untreated. Gas chromatography (GC) and liquid chromatography (LC) time-of-flight mass-spectrometry (TOF-MS) were combined to analyse foliar compounds, including central primary and specialized defensive plant metabolites.ResultsPlant responses were stronger in young leaves, which simultaneously induced higher chlorophyll levels. Both MeJA and caterpillar herbivory induced similar, but not identical, accumulation of tricarboxylic acids (TCAs), glucosinolates (GSLs) and phenylpropanoids (PPs), but only caterpillar feeding led to depletion of amino acids. MeJA followed by caterpillars caused higher induction of defence compounds, including a three-fold increase in the major defence compound allyl-GSL (sinigrin). When feeding on MeJA-treated plants, caterpillars gained less weight indicative of the reduced host-plant quality and enhanced resistance.ConclusionsThe metabolomics approach showed that plant responses induced by herbivory extend beyond the regulation of defence metabolism and are tightly modulated throughout leaf development. This leads to a new understanding of the plant metabolic potential that can be exploited for future plant protection strategies.

Herbivorous Caterpillars Can Utilize Three Mechanisms to Alter Green Leaf Volatile Emission.

Green plants emit green leaf volatiles (GLVs) as a general damage response. These compounds act as signals for the emitter plant, neighboring plants, and even for insects in the ecosystem. However, when oral secretions from certain caterpillars are applied to wounded leaves, GLV emissions are significantly decreased or modified. We examined four caterpillar species representing two lepidopteran families for their capacity to decrease GLV emissions from Zea mays leaf tissue. We also investigated the source of the GLV modifying components in the alimentary tract of the various caterpillars. In Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae), Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), and Manduca sexta (Linnaeus) (Lepidoptera: Sphingidae), we found three distinct mechanisms to modify GLV emission: a heat-stable compound in the gut, a heat-labile enzyme in salivary gland homogenate (previously described in Bombyx mori (Linnaeus) (Lepidoptera: Bombycidae), and an isomerase in the salivary gland homogenate, which catalyzes the conversion of (Z)-3-hexenal to (E)-2-hexenal (previously described in M. sexta). These mechanisms employed by caterpillars to suppress or modify GLV emission suggest a counteraction against the induced indirect volatile defenses of a plant and provides further insights into the ecological functions of GLVs.

Effects of tree species diversity on insect herbivory and leaf defences in Cordia dodecandra

1. It is broadly accepted that plant diversity influences plant–herbivore interactions, yet few studies have separated damage by different herbivore species and simultaneously tested for effects on herbivory and plant defences to elucidate the mechanisms underlying such effects.2. This study tested for effects of tree species diversity on leaf damage by beetle larvae and caterpillars on Cordia dodecandra in a diversity experiment, and measured leaf chemical and physical traits to assess whether differences in herbivory underlie changes in plant traits.3. Four year‐old trees were sampled in 21 × 21‐m plots classified as monocultures of C. dodecandra or mixtures of this species plus three other tree species. Herbivory by beetle larvae and caterpillars was estimated, and we subsequently collected undamaged leaves to quantify total phenolics and condensed tannins, trichome density, and specific leaf area.4. A significant effect of diversity on herbivory by beetle larvae was found, with mixtures exhibiting an 80% lower mean value than monocultures. By contrast, there was no diversity effect on caterpillar herbivory. Additionally, a positive relationship was found between beetle larvae (but not caterpillar) damage and plant chemical defences, yet there was no effect of diversity on defences. Specific leaf area was higher and trichome density tended to be lower in mixtures than in monocultures, but neither trait was associated with herbivory, and damage did not explain diversity effects on these traits.5. These findings emphasise the importance of separating diversity effects on different herbivore species and measuring plant traits associated with herbivory to better understand controls of diversity on plant–herbivore interactions.

Oviposition preference of three lepidopteran species is not affected by previous aphid infestation in wild cabbage

AbstractSeveral studies have shown that pre‐infestation with aphids can improve plant quality for herbivorous caterpillars. This effect is often explained by the negative crosstalk between specific plant defence, signal‐transduction pathways induced by aphids and caterpillars, respectively. However, in these studies caterpillars are introduced on the plants by the researcher, whereas in nature, the adult mother often chooses the food plants for her offspring. According to the preference–performance hypothesis adult females should choose oviposition sites that result in optimal performance and survival of their offspring. In this study, we investigated whether three lepidopteran species–Pieris brassicae (L.) (Pieridae), Plutella xylostella L. (Plutellidae) and Mamestra brassicae L. (Noctuidae)–prefer aphid‐infested over clean plants. Adult females of the three species was given the choice between wild cabbage (Brassica oleracea L., Brassicaceae) plants infested with aphids, Brevicoryne brassicae (L.) (Hemiptera: Aphididae) for 3, 7, or 14 days vs. non‐infested clean plants. Pieris brassicae females was also given the choice between plants dually infested with B. brassicae aphids and P. xylostella caterpillars when the order of infestation was varied. For oviposition, adult females of all three species did not discriminate between aphid‐infested and clean plants, irrespective of the duration of aphid infestation. Also, P. brassicae females did not discriminate between sets of dually infested plants, irrespective of the order of infestation. Several mechanisms are discussed that could explain this lack of preference.

Plant, herbivore and parasitoid community composition in native Nothofagaceae forests vs. exotic pine plantations

Abstract Converting natural areas into land used for production causes dramatic changes in the configuration of landscapes. Both the loss and fragmentation of native habitats contribute to biodiversity loss world‐wide and the consequent creation of artificial edges can have a significant influence on community assembly. The conservation value of plantation forests has been identified for specific species, but it is not clear whether exotic pine plantations can also be used for the preservation of native communities in general. We studied whether community composition of different trophic levels (plants, herbivorous caterpillars, parasitoids) changed across native Nothofagaceae forests to exotic pine plantations, and whether habitat edges affected communities differently depending on the forest type considered. To accomplish this, we sampled plants, herbivorous caterpillars and parasitoids in native Nothofagaceae and exotic pine plantation forests and compared community composition of each trophic level across habitats. We found that community composition of plants, herbivorous caterpillars and parasitoids differed significantly between native and exotic plantation forests, and that variation in the composition of the upper trophic levels was strongly dependent on variation in the composition of the lower trophic level. Moreover, differences in community composition were mostly the result of species turnover, suggesting that plantations are complementary habitats for some species, but cannot be a substitute habitat for all native forest species. Furthermore, edge effects had a strong impact on the composition of native communities, such that certain species were only present in the interior of the native habitat. Synthesis and applications. Large areas of native vegetation, where the interior remains intact, are essential to preserve species that are susceptible to edge effects and that cannot occupy other habitat types. Creating straight instead of winding edges could decrease the impact that plantations have on native forests. Furthermore, increasing the representativeness of native plant communities in exotic plantation forests would cascade up to higher consumer trophic levels, considerably increasing the conservation value of these commercial stands.

Caterpillars lack a resident gut microbiome

Many animals are inhabited by microbial symbionts that influence their hosts' development, physiology, ecological interactions, and evolutionary diversification. However, firm evidence for the existence and functional importance of resident microbiomes in larval Lepidoptera (caterpillars) is lacking, despite the fact that these insects are enormously diverse, major agricultural pests, and dominant herbivores in many ecosystems. Using 16S rRNA gene sequencing and quantitative PCR, we characterized the gut microbiomes of wild leaf-feeding caterpillars in the United States and Costa Rica, representing 124 species from 15 families. Compared with other insects and vertebrates assayed using the same methods, the microbes that we detected in caterpillar guts were unusually low-density and variable among individuals. Furthermore, the abundance and composition of leaf-associated microbes were reflected in the feces of caterpillars consuming the same plants. Thus, microbes ingested with food are present (although possibly dead or dormant) in the caterpillar gut, but host-specific, resident symbionts are largely absent. To test whether transient microbes might still contribute to feeding and development, we conducted an experiment on field-collected caterpillars of the model species Manduca sexta Antibiotic suppression of gut bacterial activity did not significantly affect caterpillar weight gain, development, or survival. The high pH, simple gut structure, and fast transit times that typify caterpillar digestive physiology may prevent microbial colonization. Moreover, host-encoded digestive and detoxification mechanisms likely render microbes unnecessary for caterpillar herbivory. Caterpillars illustrate the potential ecological and evolutionary benefits of independence from symbionts, a lifestyle that may be widespread among animals.