Annual Review of Entomology - Volume 63, 2018

The braconid parasitoid wasp subfamily Microgastrinae is perhaps the most species-rich subfamily of animals on Earth. Despite their small size, they are familiar to agriculturalists and field ecologists alike as one of the principal groups of natural enemies of caterpillars feeding on plants. Their abundance and nearly ubiquitous terrestrial distribution, their intricate interactions with host insects, and their historical association with mutualistic polydnaviruses have all contributed to Microgastrinae becoming a key group of organisms for studying parasitism, parasitoid genomics, and mating biology. However, these rich sources of data have not yet led to a robust genus-level classification of the group, and some taxonomic confusion persists as a result. We present the current status of understanding of the general biology, taxonomic history, diversity, geographical patterns, host relationships, and phylogeny of Microgastrinae as a stimulus and foundation for further study. Current progress in elucidating the biology and taxonomy of this important group is rapid and promises a revolution in the classification of these wasps in the near future.

We summarize the status of semiochemical-based management of the major bark beetle species in western North America. The conifer forests of this region have a long history of profound impacts by phloem-feeding bark beetles, and species such as the mountain pine beetle (Dendroctonus ponderosae) and the spruce beetle (D. rufipennis) have recently undergone epic outbreaks linked to changing climate. At the same time, great strides are being made in the application of semiochemicals to the integrated pest management of bark beetles. In this review, we synthesize and interpret these recent advances in applied chemical ecology of bark beetles for scientists and land managers.

Tritrophic interactions between plants, herbivores, and their natural enemies are an integral part of all terrestrial ecosystems. Herbivore-induced plant volatiles (HIPVs) play a key role in these interactions, as they can attract predators and parasitoids to herbivore-attacked plants. Thirty years after this discovery, the ecological importance of the phenomena is widely recognized. However, the primary function of HIPVs is still subject to much debate, as is the possibility of using these plant-produced cues in crop protection. In this review, we summarize the current knowledge on the role of HIPVs in tritrophic interactions from an ecological as well as a mechanistic perspective. This overview focuses on the main gaps in our knowledge of tritrophic interactions, and we argue that filling these gaps will greatly facilitate efforts to exploit HIPVs for pest control.

Attract-and-kill has considerable potential as a tactic in integrated management of pests of agricultural crops, but the use of sex pheromones as attractants is limited by male multiple mating and immigration of mated females into treated areas. Attractants for both sexes, and particularly females, would minimize these difficulties. Volatile compounds derived from plants or fermentation of plant products can attract females and have been used in traps for monitoring and control, and in sprayable attract-and-kill formulations or bait stations. Recent advances in fundamental understanding of insect responses to plant volatiles should contribute to the development of products that can help manage a wide range of pests with few impacts on nontarget organisms, but theory must be tempered with pragmatism in the selection of volatiles and toxicants and in defining their roles in formulations. Market requirements and regulatory factors must be considered in parallel with scientific constraints if successful products are to be developed.

Insect behavior can be manipulated by parasites, and in many cases, such manipulation involves the central and peripheral nervous system. Neuroparasitology is an emerging branch of biology that deals with parasites that can control the nervous system of their host. The diversity of parasites that can manipulate insect behavior ranges from viruses to macroscopic worms and also includes other insects that have evolved to become parasites (notably, parasitic wasps). It is remarkable that the precise manipulation observed does not require direct entry into the insect brain and can even occur when the parasite is outside the body. We suggest that a spatial view of manipulation provides a holistic approach to examining such interactions. Integration across approaches from natural history to advanced imaging techniques, omics, and experiments will provide new vistas in neuroparasitology. We also suggest that for researchers interested in the proximate mechanisms of insect behaviors, studies of parasites that have evolved to control such behavior is of significant value.

The synthesis of vitellogenin and its uptake by maturing oocytes during egg maturation are essential for successful female reproduction. These events are regulated by the juvenile hormones and ecdysteroids and by the nutritional signaling pathway regulated by neuropeptides. Juvenile hormones act as gonadotropins, regulating vitellogenesis in most insects, but ecdysteroids control this process in Diptera and some Hymenoptera and Lepidoptera. The complex crosstalk between the juvenile hormones, ecdysteroids, and nutritional signaling pathways differs distinctly depending on the reproductive strategies adopted by various insects. Molecular studies within the past decade have revealed much about the relationships among, and the role of, these pathways with respect to regulation of insect reproduction. Here, we review the role of juvenile hormones, ecdysteroids, and nutritional signaling, along with that of microRNAs, in regulating female insect reproduction at the molecular level.

With a million described species and more than half a billion preserved specimens, the large scale of insect collections is unequaled by those of any other group. Advances in genomics, collection digitization, and imaging have begun to more fully harness the power that such large data stores can provide. These new approaches and technologies have transformed how entomological collections are managed and utilized. While genomic research has fundamentally changed the way many specimens are collected and curated, advances in technology have shown promise for extracting sequence data from the vast holdings already in museums. Efforts to mainstream specimen digitization have taken root and have accelerated traditional taxonomic studies as well as distribution modeling and global change research. Emerging imaging technologies such as microcomputed tomography and confocal laser scanning microscopy are changing how morphology can be investigated. This review provides an overview of how the realization of big data has transformed our field and what may lie in store.

The last 25 years of phylogenetic investigation into the three orders constituting the superorder Neuropterida—Raphidioptera, Megaloptera, and Neuroptera—have brought about a dramatic revision in our understanding of the evolution of lacewings, snakeflies, dobsonflies, and their diverse relatives. Phylogenetic estimations based on combined analyses of diverse data sources, ranging from adult and larval morphology to full mitochondrial genomic DNA, have begun to converge on similar patterns, many times in accordance with hypotheses put forth by Cyril Withycombe nearly a century ago. These data, in combination with information from the fossil record, have given a revised perspective on the historical evolution and classification of Neuropterida, necessitating an overhaul of their organization and providing focus and insight on fruitful future efforts for neuropterology.

Insects and mites are common inhabitants and accidental invaders of food, including durable commodities, and their presence can have both direct and indirect effects on human health. The most common direct effect is contamination of food with arthropod fragments and related contaminants, which may be allergenic or even carcinogenic. The most important indirect effect is that their presence can change the storage microenvironment, making durable products suitable for the rapid development of fungi and other microorganisms. Some of these fungi can produce toxins (e.g., aflatoxins) that endanger human health. Insects may actively or passively contribute to the spread of microorganisms, increasing product contamination, and they may host bacteria that have developed antibiotic resistance, contributing to their spread in food. Several species also may host, attract, or transmit tapeworms, predators, or parasitoids that may affect health. This review synthesizes research on these topics and suggests directions for future research.

Body size is a key life-history trait influencing all aspects of an organism's biology. Ants provide an interesting model for examining body-size variation because of the high degree of worker polymorphism seen in many taxa. We review worker-size variation in ants from the perspective of factors internal and external to the colony that may influence body-size distributions. We also discuss proximate and ultimate causes of size variation and how variation in worker size can promote worker efficiency and colony fitness. Our review focuses on two questions: What is our current understanding of factors influencing worker-size variation? And how does variation in body size benefit the colony? We conclude with recommendations for future work aimed at addressing current limitations and ask, How can we better understand the contribution of worker body-size variation to colony success? And, what research is needed to address gaps in our knowledge?

The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), is an invasive pentatomid introduced from Asia into the United States, Canada, multiple European countries, and Chile. In 2010, BMSB populations in the mid-Atlantic United States reached outbreak levels and subsequent feeding severely damaged tree fruit as well as other crops. Significant nuisance issues from adults overwintering inside homes were common. BMSB is a highly polyphagous species with a strong dispersal capacity and high reproductive output, potentially enabling its spread and success in invaded regions. A greater understanding of BMSB biology and ecology and its natural enemies, the identification of the male-produced aggregation pheromone, and the recognition that BMSB disperses into crops from adjacent wooded habitats have led to the development of behavior-based integrated pest management (IPM) tactics. Much is still unknown about BMSB, and continued long-term collaborative studies are necessary to refine crop-specific IPM programs and enhance biological control across invaded landscapes.