Annual Review of Entomology - Volume 53, 2008

This article presents an account of the development of Geoffrey Scudder's interest in entomology, with an emphasis on threads and serendipity. Early interests in Hemiptera, insect dispersal, evolution, and chemical ecology were followed by research on insect genitalia and seed bug systematics while at Oxford University. A faculty appointment in Canada led to research on water boatmen, water striders, cardenolides, faunistics, biodiversity, and habitat restoration. Since retirement, activities have diversified to include biodiversity mapping, conservation planning, and enhancing raised-bog integrity.

One of the most obvious characteristics of an insect society is reproductive cooperation. Yet insect colonies are vulnerable to reproductive parasitism, both by workers from their own colony and by workers from others. Little is known about the mechanisms insect societies have evolved to protect themselves from being exploited from within and outside the colony and the mechanisms that social parasites have evolved to circumvent these mechanisms. Here we showcase recently discovered cases of intraspecific parasitism by workers in eusocial bees. These discoveries overturn the widespread view that insect colonies are like fortresses populated by female eunuchs, and yield important insights into the mechanisms that normally enforce functional worker sterility.

The larvae of Megaselia scalaris (Diptera: Phoridae) exploit a broad spectrum of larval pabula. Consequently, the species features in a range of situations that affect the resources or well-being of humans. Furthermore, M. scalaris is readily cultured in the laboratory and is therefore favored as an experimental species for genetic, developmental, and bioassay studies. However, the extensive but widely scattered literature, reviewed herein, is frequently ignored by specialists, which gives rise to the unwitting repetition of previous work as well as insupportable proposals.

West Nile virus (WNV) (Flavivirus: Flaviviridae) is the most widespread arbovirus in the world. A significant range expansion occurred beginning in 1999 when the virus was introduced into New York City. This review highlights recent research into WNV epizootiology and epidemiology, including recent advances in understanding of the host-virus interaction at the molecular, organismal, and ecological levels. Vector control strategies, vaccines, and antivirals, which now must be considered on a global scale, are also discussed.

Edible and seminal gifts that male arthropods transfer to their mates range from important material donations to items that provide little direct benefit. Recent reviews and research have emphasized the negative effect of gifts on female fitness, suggesting that male donations reduce the female's remating rate below her optimum or even that nuptial feeding is a net detriment to her fitness. However, comparative, experimental, and natural history evidence reveal that most edible gifts of prey or glandular products provide direct benefits to females. Gifts clearly supply nutrients when females compete for them or increase mating rates when food from other sources is limited. I point out the difficulties in determining that female remating rates are suboptimal and suggest several alternative hypotheses for the apparently low female mating rates in some gift-giving species. With regard to seminal contributions (absorbed from the ejaculate), I discuss how to separate hormonal (potentially manipulative) and material-benefit effects of male secretions on females.

A forensic entomological investigation can benefit from a variety of widely practiced molecular genotyping methods. The most commonly used is DNA-based specimen identification. Other applications include the identification of insect gut contents and the characterization of the population genetic structure of a forensically important insect species. The proper application of these procedures demands that the analyst be technically expert. However, one must also be aware of the extensive list of standards and expectations that many legal systems have developed for forensic DNA analysis. We summarize the DNA techniques that are currently used in, or have been proposed for, forensic entomology and review established genetic analyses from other scientific fields that address questions similar to those in forensic entomology. We describe how accepted standards for forensic DNA practice and method validation are likely to apply to insect evidence used in a death or other forensic entomological investigation.

Because of their selectivity and safety, microbial control agents (MCAs) appear to be ready-made components of integrated pest management (IPM) systems that do not pose a threat to applicators or the environment and allow other natural enemies to function. Control of several orchard pest insects using MCAs, including viruses, Bacillus thuringiensis, fungi, and entomopathogenic nematodes (EPNs), have been demonstrated in apple, pear, stone fruits, citrus, and several nut crops. B. thuringiensis is the most used MCA for control of lepidopteran orchard pests. Significant use of EPNs in citrus for control of root weevils is also reported. The granulovirus of codling moth is used increasingly in apple and pear by organic growers, with interest also shown by conventional growers. Although some success has been achieved, in most orchard systems MCAs account for a relatively small proportion of the pest control tactics employed, and in some systems they are not used at all. Research toward improving MCA efficacy and economic competitiveness is required to enhance the role of MCAs in IPM.

Learning and memory, defined as the acquisition and retention of neuronal representations of new information, are ubiquitous among insects. Recent research indicates that a variety of insects rely extensively on learning for all major life activities including feeding, predator avoidance, aggression, social interactions, and sexual behavior. There is good evidence that individuals within an insect species exhibit genetically based variation in learning abilities and indirect evidence linking insect learning to fitness. Although insects rely on innate behavior to successfully manage many types of variation and unpredictability, learning may be superior to innate behavior when dealing with features unique to time, place, or individuals. Among insects, social learning, which can promote the rapid spread of novel behaviors, is currently known only from a few well-studied examples in social Hymenoptera. The prevalence and importance of social learning in insects are still unknown. Similarly, we know little about ecological factors that may have promoted enhanced learning abilities in insects, and whether learning has significantly contributed to speciation in insects.

Carbon dioxide (CO2) is a ubiquitous sensory cue that plays multiple roles in insect behavior. In recent years understanding of the well-known role of CO2 in foraging by hematophagous insects (e.g., mosquitoes) has grown, and research on the roles of CO2 cues in the foraging and oviposition behavior of phytophagous insects and in behavior of social insects has stimulated interest in this area of insect sensory biology. This review considers those advances, as well as some of the mechanistic bases of the modulation of behavior by CO2 and important progress in our understanding of the detection and CNS processing of CO2 information in insects. Finally, this review briefly addresses how the ongoing increase in atmospheric CO2 levels may affect insect life.

In the tobacco hornworm, Manduca sexta, 5-hydroxytryptamine (5HT) acting at the level of the antennal lobes contributes significantly to changing the moth's responsiveness to olfactory stimuli. 5HT targets K⁺ conductances in the cells, increasing the excitability of central olfactory neurons and their responsiveness to olfactory cues. Effects of 5HT modulation are apparent not only at the single cell level, but also in the activity patterns of populations of neurons that convey olfactory information from antennal lobes to higher centers of the brain. Evidence suggests that 5HT-induced changes in activity within neural circuits of the antennal lobes might also drive structural plasticity, providing the basis for longer-term changes in antennal lobe function.

Declines in bumble bee species in the past 60 years are well documented in Europe, where they are driven primarily by habitat loss and declines in floral abundance and diversity resulting from agricultural intensification. Impacts of habitat degradation and fragmentation are likely to be compounded by the social nature of bumble bees and their largely monogamous breeding system, which renders their effective population size low. Hence, populations are susceptible to stochastic extinction events and inbreeding. In North America, catastrophic declines of some bumble bee species since the 1990s are probably attributable to the accidental introduction of a nonnative parasite from Europe, a result of global trade in domesticated bumble bee colonies used for pollination of greenhouse crops. Given the importance of bumble bees as pollinators of crops and wildflowers, steps must be taken to prevent further declines. Suggested measures include tight regulation of commercial bumble bee use and targeted use of environmentally comparable schemes to enhance floristic diversity in agricultural landscapes.

The dominant and ancestral mode of sex determination in the Hymenoptera is arrhenotokous parthenogenesis, in which diploid females develop from fertilized eggs and haploid males develop from unfertilized eggs. We discuss recent progress in the understanding of the genetic and cytoplasmic mechanisms that make arrhenotoky possible. The best-understood mode of sex determination in the Hymenoptera is complementary sex determination (CSD), in which diploid males are produced under conditions of inbreeding. The gene mediating CSD has recently been cloned in the honey bee and has been named the complementary sex determiner. However, CSD is only known from 4 of 21 hymenopteran superfamilies, with some taxa showing clear evidence of the absence of CSD. Sex determination in the model hymenopteran Nasonia vitripennis does not involve CSD, but it is consistent with a form of genomic imprinting in which activation of the female developmental pathway requires paternally derived genes. Some other hymenopterans are not arrhenotokous but instead exhibit thelytoky or paternal genome elimination.

The Argentine ant, Linepithema humile, has invaded urban, agricultural, and natural habitats worldwide, causing economic damage and disrupting ecosystem processes. Introduced populations of L. humile and those of many other invasive ants tend to be unicolonial, forming expansive, multiqueened supercolonies that dominate native ant communities and challenge control practices in managed habitats. Argentine ant management typically entails the application of residual insecticide liquids, granules, or baits to only a portion of the colony, resulting in fairly rapid reinfestation. We suggest that prevailing control methodologies are incomplete and not compatible with the behavior, nesting habits, and population structure of this ant, and therefore, more aggressive management strategies are required. Successful eradication efforts against other invasive unicolonial ant species can provide useful insights for local-scale L. humile eradication.

Is the remarkable diversity in the behavior of insects reflected in the organization of their nervous systems? The ventral nerve cords (VNCs) have been described from over 300 insect species covering all the major orders. Interpreting these data in the context of phylogenetic relationships reveals remarkable diversity. The presumed ancestral VNC structure is rarely observed; instead the VNCs of most insects show extensive modification and substantial convergence. Modifications include shifts in neuromere positions, their fusion to form composite ganglia, and, potentially, their separation to revert to individual ganglia. These changes appear to be facilitated by the developmental and functional modularity of the VNC, a neuromere for each body segment. The differences in VNC structure emphasize trade-offs between behavioral requirements and the costs incurred while maintaining the nervous system and signaling between its various parts. The diversity in structure also shows that nervous systems may undergo dramatic morphological changes during evolution.

The mosquito Aedes aegypti is more widely dispersed now than at any time in the past, placing billions of humans at risk of infection with one or more of the four dengue viruses. This review presents and discusses information on mosquito-dengue infection dynamics and describes the prominent role that temperature and rainfall play in controlling dengue viral transmission including discussions of the effect of interannual climate variations and the predicted effect of global warming. Complementary human determinants of dengue epidemiology include viremia titer, variation in viremic period, enhanced viremias, and threshold viremia. Topics covered include epidemiological phenomena such as traveling waves, the generation of genetic diversity of dengue viruses following virgin soil introductions and in hyperendemic settings, and evidence for and against viral virulence as a determinant of the severity of dengue infections. Also described is the crucial role of monotypic and heterotypic herd immunity in shaping dengue epidemic behavior.

Many key advances in our understanding of firefly biology and signaling have been made over the past two decades. Here we review this recent research, which includes new phylogenetic results that shed light on the evolution of courtship signal diversity within the family Lampyridae, new insights into firefly flash control, and the discovery of firefly nuptial gifts. We present a comprehensive overview of sexual selection in lampyrids, including evidence from Photinus fireflies that females choose their mates on the basis of male flash signals, and discuss the importance of examining both precopulatory and postcopulatory sexual selection in this group. Finally, we review recent findings on firefly chemical defenses, and discuss their implications for flash signal evolution in response to generalist predators as well as specialist predatory fireflies. This review provides new insight into how firefly flash signals have been shaped by the dual evolutionary processes of sexual selection (mate choice) and natural selection (predation), and proposes several exciting directions for future research.

Tick-borne diseases are on the rise. Lyme borreliosis is prevalent throughout the Northern Hemisphere, and the same Ixodes tick species transmitting the etiologic agents of this disease also serve as vectors of pathogens causing human babesiosis, human granulocytic anaplasmosis, and tick-borne encephalitis. Recently, several novel agents of rickettsial diseases have been described. Despite an explosion of knowledge in the fields of tick biology, genetics, molecular biology, and immunology, transitional research leading to widely applied public health measures to combat tick-borne diseases has not been successful. Except for the vaccine against tick-borne encephalitis virus, and a brief campaign to reduce this disease in the former Soviet Union through widespread application of DDT, success stories in the fight against tick-borne diseases are lacking. Both new approaches to tick and pathogen control and novel ways of translating research findings into practical control measures are needed to prevent tick-borne diseases in the twenty-first century.

Charles Darwin first became interested in entomology during his childhood, and this interest grew into a beetle-collecting obsession during his college days. Following the voyage of the Beagle, his focus on insects shifted from collecting specimens to searching for insect observations that supported his theory of natural selection as proposed in On the Origin of Species. Initially, Darwin believed that entomologists were opposed to his views. Using Darwin's correspondence, I show that his perception was based, in part, on three reviews, including one that he erroneously attributed to an entomological critic, and that not all entomologists were opposed to his ideas. Henry Walter Bates, discoverer of Batesian mimicry, voiced his support of Darwin in his papers and during meetings of the (now Royal) Entomological Society. In America, entomologist Benjamin D. Walsh wrote to Darwin in 1864, expressing his support and promising to counter any anti-Darwinian attack, and by 1868, Darwin was enjoying significant entomological support on both sides of the Atlantic. After his death in 1882, Darwin's supporters gained influence in Britain and the United States, completing entomology's shift to a Darwinian perspective.

Parasitoids display remarkable inter- and intraspecific variation in their reproductive and associated traits. Adaptive explanations have been proposed for many of the between-trait relationships. We present an overview of the current knowledge of parasitoid reproductive biology, focusing on egg production strategies in females, by placing parasitoid reproduction within physiological and ecological contexts. Thus, we relate parasitoid reproduction both to inter- and intraspecific patterns of nutrient allocation, utilization, and acquisition, and to key aspects of host ecology, specifically abundance and dispersion pattern. We review the evidence that resource trade-offs underlie several key intertrait correlations and that reproductive and feeding strategies are closely integrated at both the physiological and the behavioral levels. The idea that parasitoids can be divided into capital-breeders or income-breeders is no longer tenable; such terminology is best restricted to the females’ utilization of particular nutrients.