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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.

Weeds are a major constraint to agricultural production, particularly in the developing world. Cost-efficient biological control is a self-sustaining way to reduce this problem, and produces fewer non-target effects than chemical methods, which can cause serious damage to the environment. This book covers the origin, distribution, and ecology of twenty model invasive weed species, which occur in habitats from tropical to temperate to aquatic. Sustainable biological control of each weed using one or more arthropods is discussed. The aim is to provide ecological management models for use across the tropical world, and to assist in the assessment of potential risks to native and economic plants. This is a valuable resource for scientists and policy makers concerned with the biological control of invasive tropical plants.

Interspecific competition between phytophagous insects can occur when plant responses induced by an early-season herbivore alter host quality for later colonizers. Recent evidence for specificity in the elicitation of induced plant responses by different attackers suggests that dynamics of host use in the field may be more complex than previously anticipated, because host suitability for colonizing herbivores may depend on which herbivore species has initially damaged a plant. In each of two years, we manipulated the first herbivore to attack Solarium dulcamara plants in an experimental population using several different arthropod species and subsequently monitored colonization by natural herbivores over the course of the growing season. We additionally performed weekly herbivore counts in wild S. dulcamara populations following natural variation in herbivore arrival. Plant-mediated interactions occurred primarily between two leaf-feeding beetles, Psylliodes affinis and Plagiometriona clavata. In both manipulative and observational experiments, P. clavata oviposition was reduced on plants initially damaged by P. affinis (or a third leaf-feeding beetle, Lema trilinea) relative to plants that were initially undamaged. Lowered P. clavata occurrence continued through subsequent life-history stages, resulting in decreased emergence of second-generation P. clavata adults on these plants. The occurrence of P. affinis was also lowered on plants damaged by conspecifics in both manipulative and observational experiments. Resistance against P. affinis also followed applications of jasmonic acid, an elicitor of plant defensive responses. Conversely, early-season damage by P. clavata did not influence plant quality for either later conspecifics or P. affinis. Initial herbivory by the spittlebug Aphrophora saratogensis or generalist taildropper slugs (Prophysaon sp.) likewise had no influence on P. clavata and P. affinis colonization, whereas L. trilinea damage did not affect later arriving P. affinis. Hence, only a subset of early-season damagers influenced herbivore occurrence on S. dulcamara. Preference tests examining P. affinis feeding and P. clavata oviposition confirmed that specificity in elicitation of induced plant responses produced the divergent herbivore occurrence patterns observed in the field. Overall, the existence of plant-mediated competitive asymmetry between herbivore species on S. dulcamara highlights the dynamic nature of plant resistance and its potential role in organizing herbivore communities.

A growing body of evidence indicates that plants can influence the survival and reproduction of the insect herbivores they host via both herbivore density-dependent and density-independent processes. A remaining challenge is identifying how density-dependent and density-independent processes in herbivores contribute to the distribution of herbivores in natural populations. I tested which herbivore recruitment parameters-the intrinsic rate of increase, carrying capacity, or shape of density dependence-contributed to variance in the distribution of a gall-making fly among individuals of its host plant by experimentally manipulating herbivore density on plants in the field. I used model selection to determine the relationships between herbivore demographic parameters and the natural, pre-experimental pattern of herbivore abundances. The naturally occurring pattern of herbivore abundances before the experiment covaried positively with the herbivore carrying capacity, a parameter inversely related to the strength of density dependence, but not with the shape of density dependence or the intrinsic reproductive rate. This means that plants with high natural herbivore abundances had lower herbivore density dependence but not higher rates of herbivore reproduction at low abundances. More generally, these results suggest that density dependence mediated through the host plant was responsible for the significant spatial variance in abundance of this herbivore among host plants. This also means that the processes influencing the spatial variance in the abundance of this herbivore occur at high, but not at low, herbivore density. This suggests that when measuring parameters of herbivore preference for, or performance on, plants with different genotypes or phenotypes, ecologists should use a range of herbivore densities to ensure that they capture density-dependent processes. Density-dependent recruitment at the scale of host plants could be a widespread determinant of abundance patterns for the many insect herbivores that have high heterogeneity in abundances among host plants and low variance in that pattern through time.

Although it is well known that insects are sensitive to temperature, how they will be affected by ongoing global warming remains uncertain because these responses are multifaceted and ecologically complex. We reviewed the effects of climate warming on 31 globally important phytophagous (plant-eating) insect pests to determine whether general trends in their responses to warming were detectable. We included four response categories (range expansion, life history, population dynamics, and trophic interactions) in this assessment. For the majority of these species, we identified at least one response to warming that affects the severity of the threat they pose as pests. Among these insect species, 41% showed responses expected to lead to increased pest damage, whereas only 4% exhibited responses consistent with reduced effects; notably, most of these species (55%) demonstrated mixed responses. This means that the severity of a given insect pest may both increase and decrease with ongoing climate warming. Overall, our analysis indicated that anticipating the effects of climate warming on phytophagous insect pests is far from straightforward. Rather, efforts to mitigate the undesirable effects of warming on insect pests must include a better understanding of how individual species will respond, and the complex ecological mechanisms underlying their responses.

INTRODUCTION: In the past decade ecological speciation has been recognized as having an important role in the diversification of plant-feeding insects. Aphids are host-specialised phytophagous insects that mate on their host plants and, as such, they are prone to experience reproductive isolation linked with host plant association that could ultimately lead to species formation. The generality of such a scenario remains to be tested through macroevolutionary studies. To explore the prevalence of host-driven speciation in the diversification of the aphid genus Cinara and to investigate alternative modes of speciation, we reconstructed a phylogeny of this genus based on mitochondrial, nuclear and Buchnera aphidicola DNA sequence fragments and applied a DNA-based method of species delimitation. Using a recent software (PhyloType), we explored evolutionary transitions in host-plant genera, feeding sites and geographic distributions in the diversification of Cinara and investigated how transitions in these characters have accompanied speciation events. RESULTS: The diversification of Cinara has been constrained by host fidelity to conifer genera sometimes followed by sequential colonization onto different host species and by feeding-site specialisation. Nevertheless, our analyses suggest that, at the most, only half of the speciation events were accompanied by ecological niche shifts. The contribution of geographical isolation in the speciation process is clearly apparent in the occurrence of species from two continents in the same clades in relatively terminal positions in our phylogeny. Furthermore, in agreement with predictions from scenarios in which geographic isolation accounts for speciation events, geographic overlap between species increased significantly with time elapsed since their separation. CONCLUSIONS: The history of Cinara offers a different perspective on the mode of speciation of aphids than that provided by classic models such as the pea aphid. In this genus of aphids, the role of climate and landscape history has probably been as important as host-plant specialisation in having shaped present-day diversity.

The intimate associations between plants and the insects that eat them have helped define and shape both groups for millions of years. This pioneering volume is a comprehensive, up-to-date treatment of the evolutionary biology of herbivorous insects, including their relationships with host plants and natural enemies. Chapters focus on the dynamic relationships between insects and plants from the standpoint of evolutionary change at different levels of biological organization—individuals, populations, species, and clades. Written by prominent evolutionary biologists, entomologists, and ecologists, the chapters are organized into three sections: Evolution of Populations and Species; Co- and Macroevolutionary Radiation; and Evolutionary Aspects of Pests, Invasive Species, and the Environment. The volume is unified by the idea that understanding the ecological framework of the interactions between herbivorous insects and their host plants is fundamental to understanding their evolution.

Kavayva Zhang, Silvestre & Gates, gen. nov. , and two species are described from the Neotropics, Kavayva bodoquenensis Zhang, Silvestre & Gates, sp. nov. , and Kavayva davidsmithi , Zhang & Gates, sp. nov. Specimens of the new species were collected independently during separate research efforts in Peru and Brazil, reared from the seeds of Guarea F. Allam ex L. (Meliaceae), which represents a new host plant family for Eurytomidae. A differential diagnosis of the New World seed-feeding eurytomids is also provided.

The phenology of insect emergence affects reproductive success and is especially critical in short-lived species. An increasing number of studies have documented the effects of thermal and other climatic variations and of unpredictable habitats on the timing of adult insect emergence within and between populations and years. Numerous interacting factors may affect the phenology of adult emergence. Host-plant quality and availability is a key factor that has been largely neglected in studies of the phenology of phytophagous insects. The purpose of this study was to determine the effect of host plant characteristics on the rate of larval growth and the pattern of emergence in a wild population of Lobesia botrana (European grapevine moth), a significant pest in European vineyards. The phenology of emergence differed significantly among the six tested varieties of grapes. The percentage of bunches harboring pupae was similar among the different grape varieties, and the total number of pupae collected was similar to the number of emerging adults per bunch. Among the six varieties of grapes, 0–25 pupae were produced on each bunch. Each of the grape varieties had a single wave of emergence, in which males emerged before females, but their emergence phenology differed significantly in Chardonnay, Chasselas, and Pinot grapes. Both genders had extended durations of emergence in Merlot grapes. Together, the present results show that the characteristics of the grape host plant affect the emergence phenology of L. botrana.

Elucidating the relative strength of top-down and bottom-up forces in communities of phytophagus insects has been a major historical focus. Current consensus is that both forces play a role, but it is poorly known if these forces act differently on herbivores in the same assemblage and what factors underlie this variation. Using manipulative experiments with an assemblage of sap-feeding phytophagous insects (six species of planthoppers, leafhoppers, and heteropteran bugs) inhabiting intertidal Spartina marshes, we examined the association between herbivore behavior, risk of predation, and ultimately the relative impact of top-down (wolf spider predation) and bottom-up (host-plant nutrition) factors on the population density of each sap-feeding herbivore. A factorial experiment on open Spartina islets in the field (two levels of plant nutrition crossed with two levels of spider predation) showed that bottom-up and top-down manipulations differentially affected the various sap-feeders. Overall, bottom-up effects dominated in this sap-feeder community, whereby the density of all six sap-feeders increased when the nitrogen content of Spartina was elevated. By contrast, wolf-spider addition significantly suppressed populations of only the Prokelisia species and had little impact on the other four sap-feeder species in the community. Functional-response experiments and behavioral studies revealed that certain species (Prokelisia planthoppers) were at much higher risk of attack by wolf spiders than other sap-feeders in the assemblage and that risk of predation was associated with a species' particular \"escape/defensive behavior.\" Moreover, risk of spider predation was roughly linked to the strength of top-down impacts in the field, because species with ineffective escape behaviors and a high risk of spider attack (Prokelisia planthoppers) were the only sap-feeders whose populations were suppressed by spider predation in the field. Thus, specific behavioral characteristics of the sap-feeders on Spartina influenced risk of predation and the relative strength of top-down and bottom-up impacts on their population dynamics. Notably, all herbivores in this system were positively influenced by elevated plant nutrition, only the common sap-feeder species (Prokelisia planthoppers) were adversely affected by spider predation, and it was the rarer sap-feeders in the assemblage that were least impacted by predation. These results call into question the overall pervasiveness of top-down forces and underscore the primacy of basal resources in structuring this community of phytophagous insects.