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A chamber, named SOIL-INSECT toolbox, was developed to analyse the effect of various factors on the behaviour of soil-dwelling insects. It is equipped with sensors that continuously monitor the concentration of CO2 in the different compartments of the chamber without disturbing the air balance in the soil. The chamber can be adapted to study different stimuli, including volatile compounds, both in the presence and absence of plants. The chamber was tested using the larvae of Melolontha spp., which confi rmed its suitability for carrying out complex studies on insect-insect and insect-plant-microbiome interactions in a complex environment such as soil. The results of behavioural experiments using L3 larvae of Melolontha spp. in sterilized and natural soils revealed that the soil condition affected the behaviour of the larvae, likely due to its effect on the soil microbiome and physicochemical characteristics.

Most herbivorous insects are diet specialists in spite of the apparent advantages of being a generalist. This conundrum might be explained by fitness trade‐offs on alternative host plants, yet the evidence of such trade‐offs has been elusive. Another hypothesis is that specialization is nonadaptive, evolving through neutral population‐genetic processes and within the bounds of historical constraints. Here, we report on a striking lack of evidence for the adaptiveness of specificity in tropical canopy communities of armored scale insects. We find evidence of pervasive diet specialization, and find that host use is phylogenetically conservative, but also find that more‐specialized species occur on fewer of their potential hosts than do less‐specialized species, and are no more abundant where they do occur. Of course local communities might not reflect regional diversity patterns. But based on our samples, comprising hundreds of species of hosts and armored scale insects at two widely separated sites, more‐specialized species do not appear to outperform more generalist species., In tropical canopies, we find evidence that diet specialization in armored scale insects might be nonadaptive. Diet generalists occur on more of their potential host plants and are no less abundant than diet specialists.

1. Plants interact with various organisms, aboveground as well as belowground. Such interactions result in changes in plant traits with consequences for members of the plant-associated community at different trophic levels. Research thus far focussed on interactions of plants with individual species. However, studying such interactions in a community context is needed to gain a better understanding. 2. Members of the aboveground insect community induce defences that systemically influence plant interactions with herbivorous as well as carnivorous insects. Plant roots are associated with a community of plant-growth promoting rhizobacteria (PGPR). This PGPR community modulates insect-induced defences of plants. Thus, PGPR and insects interact indirectly via plant-mediated interactions. 3. Such plant-mediated interactions between belowground PGPR and aboveground insects have usually been addressed unidirectionally from belowground to aboveground. Here, we take a bidirectional approach to these cross-compartment plant-mediated interactions. 4. Recent studies show that upon aboveground attack by insect herbivores, plants may recruit rhizobacteria that enhance plant defence against the attackers. This rearranging of the PGPR community in the rhizosphere has consequences for members of the aboveground insect community. This review focusses on the bidirectional nature of plant-mediated interactions between the PGPR and insect communities associated with plants, including (a) effects of beneficial rhizobacteria via modification of plant defence traits on insects and (b) effects of plant defence against insects on the PGPR community in the rhizosphere. We discuss how such knowledge can be used in the development of sustainable crop-protection strategies.

Herbivore-induced plant volatiles play important ecological roles in defense against stresses. However, if and which volatile(s) are involved in the plant-plant communication in response to herbivorous insects in tea plants remains unknown. Here, plant-plant communication experiments confirm that volatiles emitted from insects-attacked tea plants can trigger plant resistance and reduce the risk of herbivore damage by inducing jasmonic acid (JA) accumulation in neighboring plants. The emission of six compounds was significantly induced by geometrid Ectropis obliqua, one of the most common pests of the tea plant in China. Among them, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) could induce the accumulation of JA and thus promotes the resistance of neighboring intact plants to herbivorous insects. CsCYP82D47 was identified for the first time as a P450 enzyme, which catalyzes the final step in the biosynthesis of DMNT from (E)-nerolidol. Down-regulation of CsCYP82D47 in tea plants resulted in a reduced accumulation of DMNT and significantly reduced the release of DMNT in response to the feeding of herbivorous insects. The first evidence for plant-plant communication in response to herbivores in tea plants will help to understand how plants respond to volatile cues in response to herbivores and provide new insight into the role(s) of DMNT in tea plants.

Made available in DSpace on 2022-05-01T05:29:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-09-01 Intensification of urbanization has been shown to be associated with taxonomic and functional modifications of biological communities, leading to changes in trophic interactions. These changes may reduce the delivery of ecosystem services provided by urban ecosystems. For instance, predation on herbivorous insects is an important ecological process operating in urban biological communities. Specifically, on one hand, herbivorous insects serve as food resources for many organisms, and on the other hand predation on herbivorous insects may reduce pest populations on urban vegetation. In this study, we assessed the relationship between urbanization intensity and bird and arthropod predation pressure on herbivorous insects across the streetscape of Xalapa (Mexico), a Neotropical city with half a million people immersed in a cloud forest context. We exposed dummy caterpillar models at 16 sites across the streetscape and two sites in a peri-urban cloud forest patch, comprising a wide range of urbanization intensities. We observed that in streets where the proportion of built cover was higher, dummy caterpillars’ attack probability was substantially lower. Moreover, we observed that caterpillars were most often attacked by arthropods (62.41%), followed by birds (21.53%), independent of built cover. Our study provides evidence that built cover surrounding streets may negatively influence the interactions between herbivorous insects and their natural enemies. Spatial Ecology and Conservation Lab (LEEC) Department of Biodiversity Institute of Biosciences Sao Paulo State University - UNESP Red de Ambiente y Sustentabilidad Instituto de Ecología A.C. Red de Biología Evolutiva Instituto de Ecología A.C. Red de Ecoetología Instituto de Ecología A.C. Spatial Ecology and Conservation Lab (LEEC) Department of Biodiversity Institute of Biosciences Sao Paulo State University - UNESP

Herbivorous insects represent one of the major threats to sessile plants. To cope with herbivore challenges, plants have evolved sophisticated defense systems, in which the lipid-derived phytohormone jasmonate plays a crucial role. Perception of insect attack locally and systemically elicits rapid synthesis of jasmonate, which is perceived by the F-box protein COI1 to further recruit JAZ repressors for ubiquitination and degradation, thereby releasing transcription factors that subsequently activate plant defense against insect attack. Here, we review recent progress in understanding the molecular basis of jasmonate action in plant defense against insects.

Trees are large organisms that structure forest ecosystems by providing an environment for an enormous diversity of animal, microbial and plant species. As these species use trees as their common hosts, many are likely to interact with each other directly or indirectly. From studies on herbaceous plant species we know that microbes can affect the interaction of plants with herbivorous insects, for example via changes in plant metabolite profiles. The consequences of fungal colonization for tree-insect interactions are, however, barely known, despite the importance of these ecological communities. In this review we explore the interaction of leaf-inhabiting pathogenic and endophytic fungi with trees and the consequences for tree-living insect herbivores. We discuss molecular, physiological, chemical, biochemical and ecological aspects of tree-fungus interactions and summarize the current knowledge on the direct and indirect effects of tree-inhabiting fungi on insect herbivores. Our mechanistic understanding of the tripartite interaction of trees with leaf-inhabiting fungi and insect herbivores is still in its infancy. We are currently facing substantial drawbacks in experimental methodology that prevent us from revealing the effect of one single fungal species on a particular insect herbivore species and vice versa. Future studies applying a versatile toolbox of modern molecular, chemical analytical and ecological techniques in combined laboratory and field experiments will unequivocally lead to a better understanding of fungus-tree-insect interactions.

AIM: The strength of species interactions is traditionally expected to increase toward the Equator. However, recent studies have reported opposite or inconsistent latitudinal trends in the bottom-up (plant quality) and top-down (natural enemies) forces driving herbivory. In addition, these forces have rarely been studied together thus limiting previous attempts to understand the effect of large-scale climatic gradients on herbivory. LOCATION: Europe. TIME PERIOD: 2018–2019. MAJOR TAXA STUDIED: Quercus robur. METHODS: We simultaneously tested for latitudinal variation in plant–herbivore–natural enemy interactions. We further investigated the underlying climatic factors associated with variation in herbivory, leaf chemistry and attack rates in Quercus robur across its complete latitudinal range in Europe. We quantified insect leaf damage and the incidence of specialist herbivores as well as leaf chemistry and bird attack rates on dummy caterpillars on 261 oak trees. RESULTS: Climatic factors rather than latitude per se were the best predictors of the large-scale (geographical) variation in the incidence of gall-inducers and leaf-miners as well as in leaf nutritional content. However, leaf damage, plant chemical defences (leaf phenolics) and bird attack rates were not influenced by climatic factors or latitude. The incidence of leaf-miners increased with increasing concentrations of hydrolysable tannins, whereas the incidence of gall-inducers increased with increasing leaf soluble sugar concentration and decreased with increasing leaf C : N ratios and lignins. However, leaf traits and bird attack rates did not vary with leaf damage. MAIN CONCLUSIONS: These findings help to refine our understanding of the bottom-up and top-down mechanisms driving geographical variation in plant–herbivore interactions, and indicate the need for further examination of the drivers of herbivory on trees. This study was carried out with financial support from the French National Research Agency (ANR) in the frame of the Investments for the Future Programme, within the Cluster of Excellence COTE (Continental To coastal Ecosystems: evolution, adaptability and governance) (ANR-10-LABX-45). E.V.C. was funded by the BiodivERsA (BiodivERsA is a network of national and regional funding organisations promoting pan-European research on biodiversity and ecosystem services, and offering innovative opportunities for the conservation and sustainable management of biodiversity) project SPONFOREST (Unraveling the potential of spontaneous forest establishment for improving ecosystem functions and services in dynamic landscapes) (BiodivERsA3-2015-58). info:eu-repo/semantics/publishedVersion

Predicting how climate change affects biotic interactions and their evolution poses a challenge. Plant-insect herbivore interactions are particularly sensitive to climate change, as climate-induced changes in plant quality cascade into the performance of insect herbivores. Whereas the immediate survival of herbivore individuals depends on plastic responses to climate change induced nutritional stress, long-term population persistence via evolutionary adaptation requires genetic variation for these responses. In order to assess the prospects for population persistence under climate change, it is therefore crucial to characterise response mechanisms to climate change induced stressors, and quantify their variability in natural populations. Here, we test developmental and transcriptomic responses to water limitation induced host plant quality change in a Glanville fritillary butterfly (Melitaea cinxia) metapopulation. We combine nuclear magnetic resonance spectroscopy on the plant metabolome, larval developmental assays and an RNA seq analysis of the larval transcriptome. We observed that responses to feeding on water limited plants, in which amino acids and aromatic compounds are enriched, showed marked intrapopulation variation, with individuals of some families performing better on control and others on water limited plants. The transcriptomic responses were concordant with the developmental responses: Families exhibiting opposite developmental responses also produced opposite transcriptomic responses, e.g. in growth associated intracellular signalling. The opposite developmental and transcriptomic responses are associated with between families differences in organic compound catabolism and storage protein production. The results reveal heritable intrapopulation variability in plasticity, suggesting potential for evolutionary responses to drought-induced changes in host plant quality in the Finnish M. cinxia metapopulation.

As massive, sessile and long-lived organisms, Mediterranean pines are exposed to a wide array of insect herbivores that feed on their tissues causing damage and ultimately, tree death. To protect themselves against biotic risks, pines have a complex battery of chemical and physical defenses, that act directly to kill or repel the antagonist organisms. Defense production, however, is not constant throughout time, but can be fine-tuned to the particular biotic risk to which the individuals and populations are exposed, producing the so called induced defenses. Moreover, the defensive state of a tree might also be determined by mutualistic interactions between the tree and other organisms that act as indirect defenses by means of top-down effects on the herbivore populations. Knowledge about these intriguing interactions in Mediterranean pines is still very limited but most of the theoretical progress made in model plant species could be hopefully translated to these long-lived plants. The defensive arsenal that a tree produces requires large amounts of resources that are no longer available for other life functions (i.e. growth, reproduction). Pine resistance to biotic threats must thus be understood as a general function integrated with other life-history traits, where defensive allocation, ultimately leading to biotic resistance, is shaped by the optimal resource allocation across life functions according to the particular biotic and abiotic environment. Thus, environmental variation across the distribution range of Mediterranean pines generates patterns of phenotypic diversity in defensive investment, by means of both adaptive (genetic) and plastic responses. Genetic variation and plasticity in the expression of defenses in Meditteranean pines have inmidiate implications in the resistance capacity of these long-lived species. Understanding the sources of phenotypic variation driving allocation to defenses in Mediterranean pines is therefore specially relevant to forecast species responses to ongoing environmental changes, particularly those casued by increased biotic stresses associated with global change.

Plants possess their own defence mechanisms to combat infestations of herbivorous insects and pathogens. It has few preexisting defence mechanisms, whereas most of the defence response is activated only after insect or pathogen invasion. Crosstalk between defence signalling pathways induced in response to herbivore/pathogen attack offer plants to regulate defence mechanism in an effective manner. Crosstalk and interaction of signalling pathways can function synergistically, or either one is suppressed under stress condition. Crosstalk enables the plant to utilize less energy for defence response and allocate energy for its growth and development. Host plant resistance against herbivores can be manipulated using chemical elicitors, which induces defence signalling mechanism in plants. Unravelling of defence mechanisms and phytohormonal signalling pathway under stress condition, the induced responses of the herbivores can be predicted, that can be further utilized for pest management and reduction in crop losses.

Insect-associated microbes, including pathogens, parasites, and symbionts, influence the interactions of herbivorous insects and pollinators with their host plants. Moreover, herbivory-induced changes in plant resource allocation and defensive chemistry can influence pollinator behavior. This suggests that the outcomes of interactions between herbivores, their microbes and host plants could have implications for pollinators. As epizootic diseases occur at high population densities, pathogen and parasite-mediated effects on plants could have landscape-level impacts on foraging pollinators. The goal of this minireview is to highlight the potential for an herbivore's multitrophic interactions to trigger plant-mediated effects on the immunity and health of pollinators. We highlight the importance of plant quality and gut microbiomes in bee health, and how caterpillars as model herbivores interact with pathogens, parasites, and symbionts to affect plant quality, which forms the centerpiece of multitrophic interactions between herbivores and pollinators. We also discuss the impacts of other herbivore-associated factors, such as agricultural inputs aimed at decreasing herbivorous pests, on pollinator microbiomes.

The latitudinal biotic interaction hypothesis (LBIH) predicts that the strength of various biotic interactions decreases from low to high latitudes. Inconsistency between studies testing this hypothesis may result from variations among different types of interactions and among study systems. Therefore, exploration of multiple interactions within one system would help to disentangle latitudinal patterns across individual interactions and to evaluate latitudinal changes in the overall impact of enemies on prey. We tested the prediction based on the LBIH that the pressure of natural enemies on herbivorous insects decreases with increase in latitude across the boreal forest zone. We also asked whether the impacts of major groups of these enemies exhibit similar latitudinal patterns and whether these patterns are consistent across study years. In 10 forest sites located from 60°N to 69°N in Northern Europe, each summer, from 2016 to 2019, we measured (a) mortality of three groups of leafmining insects caused by birds, ants, parasitoids and unknown factors, (b) bird attacks on caterpillar-shaped plasticine models and (c) birch foliar damage caused by defoliators and leafminers. Latitudinal patterns in both insect herbivory on birch and top-down pressure on herbivorous insects varied considerably and inconsistently among the four study years, so that only some of the year-specific correlations with latitude were statistically significant. Nevertheless, meta-analysis combining correlations across years, preys and enemies revealed general decreases in predation by birds (on both natural and model prey) and ants, but an increase in parasitism rates, from low to high latitudes. We found that the direction of latitudinal changes in the strength of biotic interactions was interaction-specific: predation and herbivory supported LBIH, whereas parasitism exhibited an opposite trend. Consequently, the overall impact of natural enemies on herbivorous insects did not change with latitude and was therefore an unlikely reason for the poleward decrease in herbivory observed in our gradient. Considerable among-year variation in the strength of the latitudinal patterns in all the studied interactions suggests that this variation is a widespread phenomenon.

Leaf rolls by herbivorous insects evolved in various lepidopteran groups, aphids, and some attelabid weevil species. Leaf rolls are known to have a positive effect on the survival of immature insects, protecting them from natural enemies such as birds, ants, predatory wasps, and parasitoids as well as environmental stress. On the other hand, leaf rolls are considered to have a negative effect on immature survival, attracting natural enemies because of their noticeability and subsequent learning or specialization. In this study, we directly tested the effects of leaf rolls using an attelabid species by comparing the fate of immature insects between artificial leaf rolls and unrolled leaves. The results showed the following positive effects of leaf rolls: avoidance of parasitism by eulophid wasps and avoidance of egg predation by unknown predators. On the other hand, a negative effect of leaf rolls was also detected, specifically and increase in mortality via leaf roll herbivory. This study indicated that leaf shelters are not only protective refuges but are also sometimes risky hiding places, although total survival rates increased in leaf shelters.

For many organisms, dispersal may be a high-risk activity, and dispersers are likely to have behavioral, physiological, or other adaptations that increase the probability they will successfully settle in new habitat. Dispersing aphids, for example, are small-bodied, relatively weak flyers that must navigate through a complex landscape where non-host species may be much more common than suitable hosts are. While previous research has focused on how dispersing aphids locate and evaluate host species, little is known about how they interact with the non-host species they encounter while host searching. Here, I report on an experiment to test the hypothesis that dispersers of Aphis fabae spend less time evaluating non-host species with which they have had prior experience than novel non-host species. Aphids consistently spent less time in contact with familiar non-host species than novel non-host species, but the magnitude of this effect varied for different non-host species. Aphids that had previously encountered rose spent less time interacting with rose than with raspberry or goldenrod, and aphids that had previously encountered raspberry spent less time interacting with raspberry than with goldenrod. Aphids that had previously encountered goldenrod showed a less pronounced and statistically non-significant reduction in time spent interacting with goldenrod relative to either raspberry or rose. The ability to recognize previously encountered non-hosts may allow aphids to navigate more efficiently through an environment in which they face many more non-hosts than hosts, and therefore increase the probability that a disperser will ultimately locate and settle on an appropriate host plant.

Interspecific hybridization is a prevalent process in plant species that may have different ecological and evolutionary consequences. Interactions with herbivorous insects may be altered because of hybridization among host plants. These changes result from the morphological, physiological and chemical traits expressed in hybrid individuals. Therefore, it is of interest to document the changes in traits such as leaf morphology and their consequences on patterns of herbivory by insects in hybrid complexes of plants. Another useful indicator that may serve to evaluate developmental instability resulting from genetic or environmental stress in hybrid plants is fluctuating asymmetry. In this study, we used two previously genetically characterized complexes of hybridizing Mexican oaks as models to compare and understand the relationships between leaf morphology, fluctuating asymmetry and herbivory levels in parental and hybrid individuals. Results indicated that in the Quercus affinis × Q. laurina complex, hybrid individuals show a distinct morphology in relation to the parental species, while in the Q. magnoliifolia × Q. resinosa complex, hybrids were similar to Q. resinosa. In both hybrid complexes, our results show that hybrid individuals have higher levels of fluctuating asymmetry and herbivory levels, which may reflect higher levels of genetic or environmental stress in comparison to the parental species. These results might help explain why oak species usually remain distinct despite the high frequency of hybridization characteristic of the genus.

A lot of evidence on the involvement of microsymbionts in the adaptation of hosts to adverse environmental impacts of both abiotic and biotic natures has recently been collected. In particular, microorganisms living in plants are involved in the development of induced systemic resistance to pathogens and pests, which allows them to be regarded as a reserve for the design of ecologically safe plant defense tools. However, the endosymbionts of herbivores are also putatively involved in both the adaptation of a macrosymbiont to the environment and the effect on host plant immune system in order to reduce the efficiency of defense responses. The obtained data show that the understanding of the mechanisms underlying the interaction of plants and pathogens or pests is incomplete without knowledge about the role of “hidden players,” microsymbionts that are present in both parties.

Woody encroachment in grasslands has become increasingly problematic globally. Grazing by domestic animals can facilitate woody encroachment by reducing competition from herbaceous plants and fire frequency. Herbivorous insects and parasitic plants can each exert forces that result in the natural biological control of encroaching woody plants through reducing seeding of their host woody plants. However, the interplay of grazing and dynamics of herbivorous insects or parasitic plants, and its effects on the potential biological control of woody encroachment in grasslands remains unclear. We investigated the flower and pod damage by herbivorous insects, and the infection rates of a parasitic plant on the shrub Caragana microphylla, which is currently encroaching in Inner Mongolia Steppe, under different grazing management treatments (33-year non-grazed, 7-year non-grazed, currently grazed). Our results showed that Caragana biomass was highest at the currently grazed site, and lowest at the 33-year non-grazed site. Herbaceous plant biomass followed the opposite pattern, suggesting that grazing is indeed facilitating the encroachment of Caragana plants in Inner Mongolia Steppe. Grazing also reduced the abundance of herbivorous insects per Caragana flower, numbers of flowers and pods damaged by insect herbivores, and the infection rates of the parasitic plant on Caragana plants. Our results suggest that grazing may facilitate woody encroachment in grasslands not only through canonical mechanisms (e.g. competitive release via feeding on grasses, reductions in fires, etc.), but also by limiting natural biological controls of woody plants (herbivorous insects and parasitic plants). Thus, management efforts must focus on preventing overgrazing to better protect grassland ecosystems from woody encroachment., Summary: Grazing can negatively affect herbivorous insects and parasitic plants on woody plants, and thus limit the effectiveness of their natural biological control effects on woody encroachment.

Brazilian peppertree, Schinus terebinthifolia Raddi (Anacardiaceae), is a South American plant that is highly invasive in Florida. The impact of insect herbivores on the performance of Brazilian peppertree was evaluated at two locations in Florida using an insecticide exclusion method. Although 38 species of insect herbivores were collected on the invasive tree, there were no differences in growth or reproductive output of insecticide protected and unprotected trees, providing evidence that insect feeding had no measurable impact on tree performance. The majority of insects collected on Brazilian peppertree were generalists, and several were serious agricultural pests.

Although comprising ~ 80% of the Earth's air, nitrogen (N), in a usable form, is a limited resource for herbivorous insects. Additionally, much of the consumed dietary N is lost through-excretion, further challenging such insects, while limiting their growth and reproduction. To meet this challenge, many insect groups have evolved symbiotic relationships with microbes, enabling success within otherwise inhospitable niches. These mutualistic microbes contribute to their hosts' N-economies through nitrogen recycling, fixation and/or upgrading, using divergent metabolic strategies with varying precursors and physiological requirements. In this chapter we highlight each strategy, organizing our discussion by insect taxonomy, while enumerating the various microbes and innovations that have converged upon N-centric, nutritive functions. Our overview places a large emphasis on N-recycling, due in part to a lack of recent reviews on this topic. In reviewing N-fixation, we take a termite-centred approach, capitalizing upon an extensive bank of research performed across several decades. We also emphasize essential amino acid (EAA) and precursor biosynthesis, discussing non-fixing, non-recycling mutualisms in which symbionts make up for dietary shortcomings and missing pathways for nutrient biosynthesis in their hosts. In these explorations, we discuss the specificity and evolutionary histories between herbivorous insect hosts and their often ancient N-metabolizing symbionts. We focus, further, on correlations between dietary evolution and altered symbioses, which cast light on the causes and consequences of these nutritional relationships. We, finally, describe the evidence supporting prior arguments for N-centric mutualisms, emphasizing how a pairing of genomics and experimentation can uncover mechanism, while pinpointing just how symbiont metabolism shapes the fitness and N-budgets of diverse, herbivorous hexapods.

The enemy-release hypothesis is one of the most popular but also most discussed hypotheses to explain invasion success. However, there is a lack of explicit, experimental tests of predictions of the enemy-release hypothesis (ERH), particularly regarding the effects of above- and belowground herbivory. Long-term studies investigating the relative effect of herbivores on invasive vs. native plant species within a community are still lacking. Here, we report on a long-term field experiment in an old-field community, invaded by Solidago canadensis s. l., with exclusion of above- and belowground insect herbivores. We monitored population dynamics of the invader and changes in the diversity and functioning of the plant community across eight years. Above- and belowground insects favoured the establishment of the invasive plant species and thereby increased biomass and decreased diversity of the plant community. Effects of invertebrate herbivores on population dynamics of S. canadensis appeared after six years and increased over time, suggesting that long-term studies are needed to understand invasion dynamics and consequences for plant community structure. We suggest that the release from co-evolved trophic linkages is of importance not only for the effect of invasive species on ecosystems, but also for the functioning of novel species assemblages arising from climate change.

The shapes of plant leaves are remarkably diverse, but their ecological functions are largely unknown. Reports on the effects of leaf shape on biotic interactions such as herbivory are especially scarce, partly because herbivorous insects rarely rely on leaf shape for host selection. Here, we show that leaf shape acts as a physical deterrent against a leaf-processing herbivore. Plants in the genus Isodon (Lamiaceae) host a specialized leaf-rolling weevil (Apoderus praecellens) whose ovipositing females process an entire leaf into a leaf roll to serve as larval food and shelter. Among the species of Isodon, I. umbrosus var. hakusanensis is exceptional in that it has deeply lobed leaves. Because leaf processing follows a consistent sequence of complex behaviours, the unusual shape of I. umbrosus leaves may disrupt this process. Under both natural and laboratory conditions, female weevils preferred I. trichocarpus, a close relative with non-lobed leaves, over I. umbrosus. Nutritional properties of the leaves do not explain this preference because weevil larvae developed equally well on both hosts. Modifying the non-lobed I. trichocarpus leaves to mimic the shape of I. umbrosus leaves also discouraged leaf processing. Leaf processing often terminated because weevils failed to complete the inspection routine on I. umbrosus leaves. Leaf shape may be an important but overlooked factor that affects the interactions between plants and leaf-processing herbivores.

Iceland is the only known terrestrial place in the subarctic North Atlantic providing a fairly continuous sedimentary and plant fossil record over the past 15 million years. While the basic palaeobotanical framework of this pattern has been well established during the last decade, less attention has been paid to the abundant insect traces on fossil leaves/leaflets. Here, we assess the diversity and frequency of insect herbivory on 4349 fossil angiosperm leaves/leaflets from six plant-bearing sedimentary formations exposed at 18 localities. By combining analyses of environmental factors, species interactions, ecology, biogeography, and the geological history, our results demonstrate how patterns of herbivory have changed over time in relation to temperature fluctuations that profoundly influenced levels of insect-mediated damage diversity and frequency. In addition, higher structural complexity, particularly the establishment of species-rich herb layer communities seems to have positively influenced the structure of insect communities in early late Miocene palaeoforests of Iceland.

Empirical studies indicate that many populations of herbivorous insects exhibit periodic outbreaks, but the intrinsic causes of this behavior are not well understood. Thus, in this study, we investigated a herbivore-plant system with time delay based on reaction-diffusion equations. Using normal formal theory and the center manifold theorem for partial functional differential equations, we show that this model exhibits the property of Hopf bifurcation. Therefore, interactions between the time delay and spatial diffusion will induce periodic outbreaks in herbivore populations. These results may suggest a new mechanism for herbivore outbreaks.

Under natural conditions, aboveground herbivory and plant-soil feedbacks (PSFs) are omnipresent interactions strongly affecting individual plant performance. While recent research revealed that aboveground insect herbivory generally impacts the outcome of PSFs, no study tested to what extent the intensity of herbivory affects the outcome. This, however, is essential to estimate the contribution of PSFs to plant performance under natural conditions in the field. Here, we tested PSF effects both with and without exposure to aboveground herbivory for four common grass species in nine grasslands that formed a gradient of aboveground invertebrate herbivory. Without aboveground herbivores, PSFs for each of the four grass species were similar in each of the nine grasslands—both in direction and in magnitude. In the presence of herbivores, however, the PSFs differed from those measured under herbivory exclusion, and depended on the intensity of herbivory. At low levels of herbivory, PSFs were similar in the presence and absence of herbivores, but differed at high herbivory levels. While PSFs without herbivores remained similar along the gradient of herbivory intensity, increasing herbivory intensity mostly resulted in neutral PSFs in the presence of herbivores. This suggests that the relative importance of PSFs for plant-species performance in grassland communities decreases with increasing intensity of herbivory. Hence, PSFs might be more important for plant performance in ecosystems with low herbivore pressure than in ecosystems with large impacts of insect herbivores.

Herbivore attack can alter plant interactions with pollinators, ranging from reduced to enhanced pollinator visitation. The direction and strength of effects of herbivory on pollinator visitation could be contingent on the type of plant tissue or organ attacked by herbivores, but this has seldom been tested experimentally. We investigated the effect of variation in feeding site of herbivorous insects on the visitation by insect pollinators on flowering Brassica nigra plants. We placed herbivores on either leaves or flowers, and recorded the responses of two pollinator species when visiting flowers. Our results show that variation in herbivore feeding site has profound impact on the outcome of herbivore–pollinator interactions. Herbivores feeding on flowers had consistent positive effects on pollinator visitation, whereas herbivores feeding on leaves did not. Herbivores themselves preferred to feed on flowers, and mostly performed best on flowers. We conclude that herbivore feeding site choice can profoundly affect herbivore–pollinator interactions and feeding site thereby makes for an important herbivore trait that can determine the linkage between antagonistic and mutualistic networks. Electronic supplementary material The online version of this article (10.1007/s00442-019-04539-1) contains supplementary material, which is available to authorized users.

Plants defend themselves against diverse communities of herbivorous insects. This requires an investment of limited resources, for which plants also compete with neighbours. The consequences of an investment in defence are determined by the metabolic costs of defence as well as indirect or ecological costs through interactions with other organisms. These ecological costs have a potentially strong impact on the evolution of defensive traits, but have proven to be difficult to quantify.We aimed to quantify the relative impact of the direct and indirect or ecological costs and benefits of an investment in plant defence in relation to herbivory and intergenotypic competition for light. Additionally, we evaluated how the benefits of plant defence balance its costs in the context of herbivory and intergenotypic competition.To this end, we utilised a functional‐structural plant (FSP) model of Brassica nigra that simulates plant growth and development, morphogenesis, herbivory and plant defence. In the model, a simulated investment in defences affected plant growth by competing with other plant organs for resources and affected the level and distribution of herbivore damage.Our results show that the ecological costs of intergenotypic competition for light are highly detrimental to the fitness of defended plants, as it amplifies the size difference between defended and undefended plants. This leads to herbivore damage counteracting the effects of intergenotypic competition under the assumption that herbivore damage scales with plant size. Additionally, we show that plant defence relies on reducing herbivore damage rather than the dispersion of herbivore damage, which is only beneficial under high levels of herbivore damage.We conclude that the adaptive value of plant defence is highly dependent on ecological interactions and is predominantly determined by the outcome of competition for light. plain language summary is available for this article.

Plants evolve diverse strategies to cope with herbivorous insects, in which the lipid-derived phytohormone jasmonic acid (JA) plays a crucial role. This study was conducted to investigate the differential responses of tomato and maize plants to Spodoptera exiguaherbivory and to clarify the role played by JA, methyl-jasmonate (MeJA) and jasmonoyl-L-isoleucine (JA-L-Ile) in their defense responses. JA, MeJA and JA-L-Ile were quantified using HPLC-MS/MS. The results showed that maize plant was more tolerant toS. exiguaherbivory than tomato. Spodopteraexigua attack induced JA, MeJA, and JA-L-Ile to high levels after 2 h of infestation in both test plants. Then, all studied JAsconcentration decreased gradually by increasing infestation time up to 1 week. JA concentration in infested maize was much higher than that in infested tomato leaves. However, MeJA concentration in infested tomato leaves was higher than that in maize. In control plants, JA was not recorded, while MeJA was recorded in comparable values both in tomato and maize. Our results showed that JA plays the main role in increasing defense responses to S. exigua infestation in the studied plants as a direct signaling molecule; however, MeJA could play an indirect role by inducing JA accumulation. JA-L-Ile indicated a less efficient role in defense responses to S. exigua attack in both test plants where its level is much lower than JA and MeJA.

Understanding the evolutionary dynamics underlying herbivorous insect mega-diversity requires investigating the ability of insects to shift and adapt to different host plants. Feeding experiments with nine related stick insect species revealed that insects retain the ability to use ancestral host plants after shifting to novel hosts, with host plant shifts generating fundamental feeding niche expansions. These expansions were, however, not accompanied by expansions of the realised feeding niches, as species on novel hosts are generally ecologically specialised. For shifts from angiosperm to chemically challenging conifer hosts, generalist fundamental feeding niches even evolved jointly with strong host plant specialisation, indicating that host plant specialisation is not driven by constraints imposed by plant chemistry. By coupling analyses of plant chemical compounds, fundamental and ecological feeding niches in multiple insect species, we provide novel insights into the evolutionary dynamics of host range expansion and contraction in herbivorous insects.

Understanding the evolutionary dynamics underlying herbivorous insect mega-diversity requires investigating the ability of insects to shift and adapt to different host plants. Feeding experiments with nine related stick insect species revealed that insects retain the ability to use ancestral host plants after shifting to novel hosts, with host plant shifts generating fundamental feeding niche expansions. These expansions were not accompanied by expansions of the realized feeding niches however, as species on novel hosts are generally ecologically specialized. For shifts from angiosperm to chemically challenging conifer hosts, generalist fundamental feeding niches even evolved jointly with strong host plant specialization, indicating that host plant specialization is more likely driven by species interactions than by constraints imposed by plant chemistry. By coupling analyses of plant chemical compounds, fundamental and ecological feeding niches in multiple insect species, we provide novel insights into the evolutionary dynamics of host range expansion and contraction in herbivorous insects.

1. Studies of grassland communities have demonstrated that increasingvertebrate grazing decreases the diversity of specialised herbivorous insects,while plant diversity is maintained or increased. However, we still have a limitedunderstanding of the causal mechanisms underlying these contrasting observations of two tightly linked groups of organisms.2. We used spatially linked plant and moth observations from salt marshes,sampled for 3 years along an experimental sheep-grazing gradient (0, 1–2, 3–4and 10 sheep ha1), to test whether the disruption of plant–insect interactionsby large herbivores accounts for these contrasting grazing effects. Moths werecaught using emergence traps, which were moved and repositioned every3 weeks.3. Firstly, we quantified species turnover between the grazing regimes forboth taxa (measured as Sørensen dissimilarity) using a null-model approach.Secondly, we analysed the number of observed insect ̶ host associations underthe different regimes.4. Species turnover between grazing regimes was significant (after correctingfor rarefaction effects) for moth species, but not for plants, indicating very fewand random effects of grazing on plant species composition. The percentage ofrealised plant–moth associations decreased from 37% in the absence of grazingto 6.5% under high stocking densities.5. We thus conclude that vertebrate grazing caused a disruption of plant–moth associations, probably by rendering the host-plants unsuitable for most ofthe moth species. Our findings provide further mechanistic understanding onhow large herbivores shape arthropod communities and illustrate the importance of host-plant associations in explaining effects of natural or anthropogenic habitat modification. 1. Studies of grassland communities have demonstrated that increasingvertebrate grazing decreases the diversity of specialised herbivorous insects,while plant diversity is maintained or increased. However, we still have a limited understanding of the causal mechanisms underlying these contrasting observations of two tightly linked groups of organisms.2. We used spatially linked plant and moth observations from salt marshes,sampled for 3 years along an experimental sheep-grazing gradient (0, 1–2, 3–4 and 10 sheep ha1), to test whether the disruption of plant–insect interactions by large herbivores accounts for these contrasting grazing effects. Moths were caught using emergence traps, which were moved and epositioned every 3 weeks.3. Firstly, we quantified species turnover between the grazing regimes forboth taxa (measured as Sørensen dissimilarity) using a null-model approach.Secondly, we analysed the number of observed insect ̶ host associations underthe different regimes.4. Species turnover between grazing regimes was significant (after correctingfor rarefaction effects) for moth species, but not for plants, indicating very fewand random effects of grazing on plant species composition. The percentage of realised plant–moth associations decreased from 37% in the absence of grazing to 6.5% under high stocking densities.5. We thus conclude that vertebrate grazing caused a disruption of plant–moth associations, probably by rendering the host-plants unsuitable for most of the moth species. Our findings provide further mechanistic understanding on how large herbivores shape arthropod communities and illustrate the importance of host-plant associations in explaining effects of natural or anthropogenic habitat modification.

Insectivorous birds are known to play a decisive role for the natural control of herbivorous insects. Thus, they enhance the growth, reproduction, and survival of plant individuals and in the long-term benefit plant regeneration. However, particularly in the tropics, forest fragmentation has been suggested to cause a loss of insectivorous birds. Yet, it is unclear whether this hampers the trophic control of herbivorous insects with potential consequences for plants. Therefore, we investigated the effect of increasing forest fragmentation on tritrophic interactions between insectivorous birds, herbivorous insects, and plants in a subtropical forest landscape, South Africa. We monitored the community composition of birds and estimated insectivorous bird abundances along a gradient of forest fragmentation. In the same sites, we installed bird exclosures on a common plant species (Englerophytum natalense) to assess effects of the trophic control of insectivorous birds on herbivorous insects and leaf area loss (LAL). Forest fragmentation strongly shaped the functional composition of bird communities, particularly through a loss of forest-dependent insectivorous birds. Moreover, LAL was higher within bird exclosures than on control branches and increased with increasing forest fragmentation on the control branches. Altogether, forest fragmentation seems to hamper the trophic control of herbivorous insects by insectivorous birds through changes in the community composition. This, in turn, may interfere with tritrophic interactions and ecological processes. Thus, conservation efforts aiming at enhancing the natural control of herbivorous insects should focus on the maintenance of continuous indigenous forests that are well-connected to smaller forest fragments on the landscape scale.

Host specialization among closely related herbivores is common and is therefore a major theme in ecology. Despite its ecological importance, no general explanatory framework for host specialization is currently available. We introduce a new model of the evolution of host specialization in herbivorous insects. We use a two-dimensional lattice comprising 32 × 32 cells. Moreover, the model incorporates reproductive interference, defined as any negative outcomes resulting from interspecific mating, between two species of herbivores feeding on two different host plants as well as ordinary resource competition and differences in host suitability. Our simulation showed that reproductive interference, together with other factors such as host-related performance and resource competition, can actually drive the evolution of host specialization and thereby host partitioning between herbivorous insects during secondary contact. Host specialization arises particularly when levels of both reproductive interference and resource competition are intermediate. In contrast, host specialization seldom occurs if reproductive interference is absent. Thus, reproductive interference is as key to specialization as is spatial partitioning, which was not regarded as a realistic outcome when only resource competition was considered.

Plant–soil feedbacks are legacy effects created by an initial plant on the growth of subsequent plants using the same soil. These indirect soil-mediated interactions are primarily studied in the context of changes in the belowground biotic community. Here, we review current evidence surrounding plant–soil feedbacks, focusing on how these interactions are studied from an experimental standpoint and expand this discussion into new directions surrounding the influence of feedbacks on interactions with aboveground herbivorous insects. The taxon-specific impact of individual soil groups on foliar-feeding insects is well-described, but expanding this framework to plant–soil feedbacks is challenging because different plant species cause simultaneous and dramatic shifts in the composition of all soil life, sometimes in contradictory directions (i.e., certain fungi may increase, while nematodes decrease). Thus, expanding simple pair-wise root herbivore–plant–insect relationships to more holistic approaches that account for the full spectrum of changes in soil biota represents both a mechanistic and analytical challenge. These community-wide shifts, however, are representative of true legacy effects encountered by plants and insects in nature. We end our chapter on a discussion of how plant–soil feedbacks can be functionally used to steer the microbiome for enhanced crop protection in applied agricultural systems.

Plants can respond to insect egg deposition and thus resist attack by herbivorous insects from the beginning of the attack, egg deposition. We review ecological effects of plant responses to insect eggs and differentiate between egg-induced plant defenses that directly harm the eggs and indirect defenses that involve egg parasitoids. Furthermore, we discuss the ability of plants to take insect eggs as warning signals; the eggs indicate future larval feeding damage and trigger plant changes that either directly impair larval performance or attract enemies of the larvae. We address the questions of how egg-associated cues elicit plant defenses, how the information that eggs have been laid is transmitted within a plant, and which molecular and chemical plant responses are induced by egg deposition. Finally, we highlight evolutionary aspects of the interactions between plants and insect eggs and ask how the herbivorous insect copes with egg-induced plant defenses and may avoid them by counteradaptations.

Plant volatiles are used not only by herbivorous insects to find their host plants, but also by the natural enemies of the herbivores to find their prey. There is also increasing evidence that plant volatiles, in addition to species-specific pheromones, help these insects to find mating partners. Plant structures such as flowers, fruit, and leaves are frequently rendezvous sites for mate-seeking insects. Here we propose that the combined use of plant volatiles and pheromones can efficiently guide insects to these sites, where they will have access to both mates and food. This notion is supported by the fact that plant volatiles can stimulate the release of sex pheromones and can render various insects more receptive to potential mates.

Chewing herbivores, such as caterpillars and beetles, while feeding on the host plant, cause extensive tissue damage and release a wide array of cues to alter plant defenses. Consequently, the cues can have both beneficial and detrimental impacts on the chewing herbivores. Herbivore-associated molecular patterns (HAMPs) are molecules produced by herbivorous insects that aid them to elicit plant defenses leading to impairment of insect growth, while effectors suppress plant defenses and contribute to increased susceptibility to subsequent feeding by chewing herbivores. Besides secretions that originate from glands (e.g., saliva) and fore- and midgut regions (e.g., oral secretions) of chewing herbivores, recent studies have shown that insect frass and herbivore-associated endosymbionts also play a critical role in modulating plant defenses. In this review, we provide an update on a growing body of literature that discusses the chewing insect HAMPs and effectors and the mechanisms by which they modulate host defenses. Novel “omic” approaches and availability of new tools will help researchers to move forward this discipline by identifying and characterizing novel insect HAMPs and effectors and how these herbivore-associated cues are perceived by host plant receptors.

Elevated ground-level ozone (O3) reduced C-based defense chemicals, however, severe grazing damages were found in leaves grown in the low O3 condition of a free air O3-concentration enrichment (O3-FACE) system. To explain this phenomenon, this study investigates the role of BVOCs (biogenic volatile organic compounds) as signaling compounds for insect herbivores. BVOCs act as scents for herbivore insects to locate host plants, while some BVOCs show high reactivity to O3, inducing changes in the composition of BVOCs in atmospheres with elevated O3. To assess the aforementioned phenomenon, profiles of BVOCs emitted from birch (Betula platyphylla var. japonica Hara) leaves were analyzed ex situ, and Y-tube insect preference tests were conducted in vitro to study the insect olfactory response. The assays were conducted in June and August or September, according to the life cycle of the adult alder leaf beetle Agelastica coerulea Baly (Coleoptera: Chrysomelidae). The Y-tube tests revealed that the leaf beetles were attracted to BVOCs, and O3 per se had neither an attractant nor a repellent effect. BVOCs became less attractant when mixed with highly concentrated O3 (&gt, 80 ppb). About 20% of the total BVOCs emitted were highly O3-reactive compounds, such as &beta, ocimene. The results suggest that BVOCs emitted from the birch leaves can be altered by elevated O3, thus potentially reducing the attractiveness of leaves to herbivorous insects searching for food.

Richness and diversity of plant and herbivorous insect species were significantly lower in abandoned and intensified grasslands than in traditional grasslands. This trend was consistent throughout the seasons in 2011 and 2012. Changes in mowing frequency and surrounding landscape due to land abandonment and intensification explained plant richness declines around paddy terraces. Declines in herbivorous insects were well explained by plant richness declines and changes in mowing frequency. Plant and herbivore richness were maximized at an intermediate mowing frequency (about twice per year), which is a typical practice on traditional terraces.

SummaryTo survive and complete their life cycle, herbivorous insects face the difficult challenge of coping with the arsenal of plant defences. A new study reports that aphids secrete evolutionarily conserved cytokines in their saliva to suppress host immune responses.

Introductions of both plants and herbivorous insects have had tremendous impacts on the world's ecosystems. Novel herbivorous insect-plant interactions are important consequences of introductions of either plants or herbivorous insects. We contrast novel herbivorous insect-plant interactions that arise due to plant versus insect introductions with the aim of understanding whether the causes and consequences of the interaction depend on which party is non-native. The biotic context of the herbivore-plant interaction, in terms of mutualists, predators, and competitors can limit the prevalence of that interaction and varies between native and introduced ranges. Introduced plants can have a large, direct impact on their environment, whereas the impact of introduced herbivorous insects is often mediated through the plants that they consume.

Herbivorous insects may have significant impacts on litter decomposi- tion through modification of plant litter quality and quantity. The effects of herbivorous insects on decomposition processes are of growing interest. 2. Here, experiments were conducted to examine how sap-feeding aphids modify plant litter and whether the aphid-induced modification influences litter decomposition processes, using a plant-herbivore system consisting of soybean (Glycine max (L.)) and soybean aphids (Aphis glycines Matsumura). 3. First, litter traits produced by aphid-free and aphid-infected plants were compared, and it was found that aphids did not affect litter mass and carbon concentration, but significantly decreased the nitrogen concentration. Such aphid-mediated modification of litter quality may cause deceleration of litter decomposition as the higher C/N ratio inhibits litter decomposition. 4. A decomposition experiment was then carried out to compare the decomposition of litter between the aphid-free and aphid-infected plants. No impacts of aphid herbivory were found on litter carbon mineralisation but negative impacts were found on nitrogen mineralisation. Litter nitrogen mineralisation of aphid-infected plants decreased by 40% and 28% compared with that of aphid-free plants 1 and 3 months after commencement of the experiment, respectively. 5. The experimental results clearly showed that aphids decelerated litter nitrogen mineralisation by modifying litter quality.

Australia harbours a very diverse phytophagous insect fauna, but little is known about the patterns of insect herbivory in dominant forest systems, especially in dry sclerophyll forests. Here, we assess variation in leaf herbivory in four species of narrow-ranged sclerophyllous shrubs across their geographical distribution. We assessed leaf herbivory as the percentage of missing leaf area, and estimated the proportion of damage types, such as chewing, sucking and mining. We found that the levels of leaf herbivory and the proportions of damage types were consistent among plant species but showed considerable variability within single plant species among sites and individual plants. This variability is most likely due to the patchy distribution of herbivorous insects in space and time. Leaf damage was dominated by chewing, but mining and sucking occurred on all plant four species. Sap sucking, although much less conspicuous, was found to be a major damage type, demonstrating that neglect of sap sucking damage in leaf herbivory assessments could lead to a considerable underestimation of the total herbivore damage inflicted on host plants.

Interactions among herbivores or between herbivores and other plant natural enemies, such as fungal pathogens, range from competition to facilitation. Moreover, the outcome of these interactions depends on the ecological context where they occur. In this study we examined the effects of clipping, as a surrogate of herbivory by ungulates, on the damage caused by two types of natural enemies (herbivorous insects and foliar fungal pathogens) on bilberry, Vaccinium myrtillus, in combination with nitrogen (N) fertilization representing current N atmospheric deposition. To examine whether the responses of both these natural enemies were mediated by changes in the plant, we estimated the effects of the treatments on bilberry growth and branching and on chlorophyll content as proxy of N content in leaves. Clipping increased the proportion of leaves damaged by herbivorous insects regardless of whether it was combined with N fertilization or not in 2008. In 2007 and 2009 repeated damage to the shrub also facilitated insect herbivory but only under N applications. Regarding fungal infestation incidence, clipping decreased the proportion of infected leaves in all the years considered but only in fertilized plots. Our results suggest that vertebrate herbivores facilitate insect herbivory and reduce fungal infestation but that these effects are dependent on nutritional conditions. Moreover, we found a negative residual correlation between insect herbivory and fungal infestation on bilberry leaves. Therefore, interactions between insect herbivores and fungal pathogens could be implicated in the final outcome of interactions between browsing ungulates and both bilberry natural enemies.

Plants and herbivores both release volatile organic compounds that have important roles in mediating important biological functions related to defence and reproduction. Plants emit complex blends of chemicals that are involved in multitrophic interactions, coordination of systemic defence responses and pollination, whereas herbivorous insects release pheromones that play important roles in attracting mates, instigating defence responses and initiating aggregation. Interactions between plants and herbivores have been subject to a wealth of studies and knowledge on their biology, biochemistry, ecology and evolution is constantly expanding. In this chapter the idea of communication between plants and herbivores will be explored. Communication between organisms of consecutive trophic levels is somewhat controversial due to unidirectional reliance and competition precluding some of the requirements of a conventional communication process, but there are growing examples of where chemically mediated interactions between plants and herbivores can be viewed as eavesdropping by a signal recipient, or even as true communication where both chemical emitter and receiver gain a benefit from communication. Examples of herbivores responding to plant-emitted cues and plants responding to herbivore-emitted cues are both explored, and suggestions for future directions in this field are provided.

Herbivorous insects have been categorized as generalists or specialists depending on the taxonomic relatedness of the plants they use as food or oviposition substrates. The plasticity in host plant selection behavior of species belonging to the two categories received little attention. In the present work, fifth instar caterpillars of the generalist herbivore Helicoverpa armigera and its closely related species, the specialist Helicoverpa assulta, were fed on common host plants or artificial diet, after which their feeding preference was assessed individually by using dual - and triple- plant choice assays. Results show both the two Helicoverpa species have a preference hierarchy for host plants. Compared to the fixed preference hierarchy of the specialist H. assulta, the generalist H. armigera exhibited extensive plasticity in feeding preference depending on the host plant experienced during larval development. Whereas the specialist H. assulta exhibited a rigid preference in both dual and triple-plant choice assays, our findings demonstrate that the generalist H. armigera expressed stronger preferences in the dual-plant choice assay than in the triple-plant choice assay. Our results provide additional evidence supporting the neural constraints hypothesis which predicts that generalist herbivores make less accurate decisions than specialists when selecting plants.

Plants respond to feeding by herbivorous insects by producing volatile organic chemicals, which mediate interactions between herbivores and plants. Yet, few studies investigated whether such plant responses to herbivory differ between historical host and novel plants. Here, we investigated whether herbivory by the pine weevil Hylobius abietis causes a release of volatile organic chemicals from a novel tree Pinus brutia and compared the relative amounts of volatiles released from herbivore's historical hosts and P. brutia. We collected volatiles emitted from P. brutia seedlings that were either subjected to feeding by H. abietis or no feeding. Our results indicated that feeding increased emission of volatile compounds, composed of monoterpenes and sesquiterpenes, and that the emission was several fold higher in the damaged seedlings than in undamaged seedlings. In particular, emission of monoterpenes and sesquiterpenes increased by 4.4-and 10-fold in the damaged plants, respectively. Strikingly, individual monoterpenes and sesquiterpenes showed much greater dissimilarity between damaged and undamaged seedlings. Furthermore, several minor monoterpenes showed negative relationships with the weevil gnawed area. We discussed these results with the results of previous studies focused on historical host plants of H. abietis and hypothesized the ecological relevance and importance of our results pertaining relevance to the plant–herbivory interactions. © 2016 Blackwell Verlag GmbH

At least half of metazoan species are herbivorous insects. Why are they so diverse? Most herbivorous insects feed on few plant species, and adaptive host specialization is often invoked to explain their diversification. Nevertheless, it is possible that the narrow host ranges of many herbivorous insects are non-adaptive. Here, we test predictions of this hypothesis with comparative phylogenetic analyses of scale insects, a group for which there appears to be few host-use tradeoffs that would select against polyphagy, and for which passive wind-dispersal should make host specificity costly. We infer a strong positive relationship between host range and diversification rate, and a marked asymmetry in cladogenetic changes in diet breadth. These results are consonant with a system of pervasive non-adaptive host specialization in which small, drift-and extinction-prone populations are frequently isolated from persistent and polyphagous source populations. They also contrast with the negative relationship between diet breadth and taxonomic diversification that has been estimated in butterflies, a disparity which likely stems from differences in the average costs and benefits of host specificity and generalism in scale insects vs. butterflies. Our results indicate the potential for non-adaptive processes to be important to diet-breadth evolution and taxonomic diversification across herbivorous insects.

Plants can respond to attack by herbivorous insects very soon after herbivores start producing a new generation by depositing eggs onto their leaves. Egg-induced plant responses may result in killing the attacker in its egg stage. However, if the eggs do survive, they can also prime feeding-induced plant defenses against the larvae hatching from eggs. In this paper we focus first on egg-induced plant responses that resemble hypersensitive responses (HR) to phytopathogens and lead to egg desiccation or detachment from plants. We then summarize the current knowledge about egg-mediated effects on feeding-induced plant defenses against larvae. Finally, we discuss the insect species specificity of plant responses to eggs and the variability of insect susceptibility to these responses.