Specific plant associations may decrease (associational resistance, AR) or increase (associational susceptibility, AS) the likelihood of detection by, and/or vulnerability to, herbivores. We discuss presumed mechanisms leading to AR and AS, suggest others, and conduct meta-analyses on plant and herbivore traits affecting AR and AS, and the effects of habitat. Specific plant associations determine the likelihood of detection and/or vulnerability of focal plants to herbivores. AS is more likely with insects and AR more likely with mammals. Unpalatable neighbors increase the likelihood of AR. An herbivore's feeding guild, diet breadth, and habitat type do not influence the likelihood of AR or AS. The effectiveness of AR in reducing herbivore abundance is independent of whether neighboring plants are within a plot of focal crops or along the edge of a plot. AR and AS may be applicable to associations among herbivores, and may be appropriately studied from a landscape perspective.

SignificanceDecades of research have fostered the now-prevalent assumption that noncrop habitat facilitates better pest suppression by providing shelter and food resources to the predators and parasitoids of crop pests. Based on our analysis of the largest pest-control database of its kind, noncrop habitat surrounding farm fields does affect multiple dimensions of pest control, but the actual responses of pests and enemies are highly variable across geographies and cropping systems. Because noncrop habitat often does not enhance biological control, more information about local farming contexts is needed before habitat conservation can be recommended as a viable pest-suppression strategy. Consequently, when pest control does not benefit from noncrop vegetation, farms will need to be carefully comanaged for competing conservation and production objectives.

Brown marmorated stink bug, Halyomorpha halys Stål, is an invasive, herbivorous insect species that was accidentally introduced to the United States from Asia. First discovered in Allentown, PA, in 1996, H. halys has now been reported from at least 40 states in the United States. Additional invasions have been detected in Canada, Switzerland, France, Germany, Italy, and Lichtenstein, suggesting this invasive species could emerge as a cosmopolitan pest species. In its native range, H. halys is classified as an outbreak pest; however, in North America, H. halys has become a major agricultural pest across a wide range of commodities. H. halys is a generalist herbivore, capable of consuming Ͼ100 different species of host plants, often resulting in substantial economic damage; its feeding damage resulted in US$37 million of losses in apple in 2010, but this stink bug species also attacks other fruit, vegetable, field crop, and ornamental plant species. H. halys has disrupted integrated pest management programs for multiple cropping systems. Pesticide applications, including broad-spectrum insecticides, have increased in response to H. halys infestations, potentially negatively influencing populations of beneficial arthropods and increasing secondary pest outbreaks. H. halys is also challenging because it affects homeowners as a nuisance pest; the bug tends to overwinter in homes and outbuildings. Although more research is required to better understand the ecology and biology of H. halys, we present its life history, host plant damage, and the management options available for this invasive pest species.

Habitat fragmentation is a complex process that affects ecological systems in diverse ways, altering everything from population persistence to ecosystem function. Despite widespread recognition that habitat fragmentation can influence food web interactions, consensus on the factors underlying variation in the impacts of fragmentation across systems remains elusive. In this study, we conduct a systematic review and meta-analysis to quantify the effects of habitat fragmentation and spatial habitat structure on resource consumption in terrestrial arthropod food webs. Across 419 studies, we found a negative overall effect of fragmentation on resource consumption. Variation in effect size was extensive but predictable. Specifically, resource consumption was reduced on small, isolated habitat fragments, higher at patch edges, and neutral with respect to landscapescale spatial variables. In general, resource consumption increased in fragmented settings for habitat generalist consumers but decreased for specialist consumers. Our study demonstrates widespread disruption of trophic interactions in fragmented habitats and describes variation among studies that is largely predictable based on the ecological traits of the interacting species. We highlight future prospects for understanding how changes in spatial habitat structure may influence trophic modules and food webs.

Previous syntheses have identified the key roles that phylogeny, body size, and trophic level play in determining arthropod stoichiometry. To date, however, detritivores have been largely omitted from such syntheses, despite their importance in nutrient cycling, biodiversity, and food web interactions. Here, we report on a compiled database of the allometry and nutritional stoichiometry (N and P) of detritivorous arthropods. Overall, both N and P content for detritivores varied among major phylogenetic lineages. Detritivore N content was similar to the N content of herbivores, but below that of predators. By contrast, detritivore P content was independent of trophic level. Contrary to previous reports, neither nutrient varied with body size. This analysis places detritivores in the context of related herbivores and predators, and as such, sets the stage for future investigations into the causes and consequences of elemental (mis)matches between detritivores and their detrital resources.