Annual Review of Entomology - Volume 52, 2007

An account of the development of biological interest, and specifically interest in bees, by Charles D. Michener. Included topics are the role of graduate students and the relationship between behavioral studies and systematics. Sections are (a) upbringing, including initiation of biological interests, (b) early studies of bees, (c) student work at the University of California, Berkeley, (d) work at the American Museum of Natural History and in the U.S. Army, and (e) work at the University of Kansas, especially wild bee behavior and bee systematics.

The effect of parasites on their hosts has implications for basic and applied ecology (e.g., species’ population dynamics and distributions, biological control, and threats to at-risk species) and coevolution. Cuterebrid bot flies comprise one of the most-studied groups of insect parasites of mammals. Interest in their impact dates from at least 1857, when Cuterebra emasculator was so named because of the erroneous belief that its larvae castrate their hosts. This review addresses the effects of cuterebrid larvae on host biochemistry, physiology, behavior, and ecology. Despite high prevalence (peak values commonly range from 30% to 70%), at average intensities (one to three larvae per host) these parasites generally have little effect on the fitness or population dynamics of their typical hosts. This outcome likely reflects parasite/host coevolution favoring parasites that minimize harmful effects on hosts required for their survival and hosts that best tolerate perennial parasites they cannot avoid. In contrast, aggravated effects occur at higher intensities and with atypical hosts. Additional field studies involving experimental manipulation of infestation and spanning more than a few seasons are required to confirm these conclusions.

For many leaf-feeding herbivores, synchrony in phenology with their host plant is crucial as development outside a narrow phenological time window has severe fitness consequences. In this review, we link mechanisms, adaptation, and population dynamics within a single conceptual framework, needed for a full understanding of the causes and consequences of this synchrony. The physiological mechanisms underlying herbivore and plant phenology are affected by environmental cues, such as photoperiod and temperature, although not necessarily in the same way. That these different mechanisms lead to synchrony, even if there is spatial and temporal variation in plant phenology, is a result of the strong natural selection acting on the mechanism underlying herbivore phenology. Synchrony has a major impact on the population densities of leaf-feeding Lepidoptera, and years with a high synchrony may lead to outbreaks. Global climate change leads to a disruption of the synchrony between herbivores and their host plants, which may have major impacts for population viability if natural selection is insufficient to restore synchrony.

Burgeoning consumer interest in organically produced foods has made organic farming one of the fastest growing segments of agriculture. This growth has not been supported adequately by rigorous research to address challenges such as arthropod pest management. The research that has been conducted, however, is complemented by research in aspects of conventional agriculture that may have applicability in organic systems, as well as by research in underpinning fields such as applied ecology. This article synthesizes the available literature in relation to a conceptual model of arthropod pest management strategies suitable for organic systems. The present work uses the four phases of the model to review the strategies in an agroecological context and provides a synthesis of the factors that influence the success of each phase. Rather than constituting a fringe science, pest management research for organic systems draws on cutting edge science in fields such as landscape and chemical ecology and has a bright future.

Traditionally, measurement of the acute toxicity of pesticides to beneficial arthropods has relied largely on the determination of an acute median lethal dose or concentration. However, the estimated lethal dose during acute toxicity tests may only be a partial measure of the deleterious effects. In addition to direct mortality induced by pesticides, their sublethal effects on arthropod physiology and behavior must be considered for a complete analysis of their impact. An increasing number of studies and methods related to the identification and characterization of these effects have been published in the past 15 years. Review of sublethal effects reported in published literature, taking into account recent data, has revealed new insights into the sublethal effects of pesticides including effects on learning performance, behavior, and neurophysiology. We characterize the different types of sublethal effects on beneficial arthropods, focusing mainly on honey bees and natural enemies, and we describe the methods used in these studies. Finally, we discuss the potential for developing experimental approaches that take into account these sublethal effects in integrated pest management and the possibility of integrating their evaluation in pesticide registration procedures.

Parasitoids depend on a series of adaptations to the ecology and physiology of their hosts and host plants for survival and are thus likely highly susceptible to changes in environmental conditions. We analyze the effects of global warming and extreme temperatures on the life-history traits of parasitoids and interactions with their hosts. Adaptations of parasitoids to low temperatures are similar to those of most ectotherms, but these adaptations are constrained by the responses of their hosts. Life-history traits are affected by cold exposure, and extreme temperatures can reduce endosymbiont populations inside a parasitoid, eventually eliminating populations of endosymbionts that are susceptible to high temperatures. In several cases, divergences between the thermal preferences of the host and those of the parasitoid lead to a disruption of the temporal or geographical synchronization, increasing the risk of host outbreaks. A careful analysis on how host-parasitoid systems react to changes in temperature is needed so that researchers may predict and manage the consequences of global change at the ecosystem level.

Until the 1980s theories of social insect evolution drew strongly on halictine and allodapine bees. However, that early work suffered from a lack of sound phylogenetic inference and detailed information on social behavior in many critical taxa. Recent studies have changed our understanding of these bee groups in profound ways. It has become apparent that forms of social organization, caste determination, and sex allocation are more labile and complex than previously thought, although the terminologies for describing them are still inadequate. Furthermore, the unexpected complexity means that many key parameters in kin selection and reproductive skew models remain unquantified, and addressing this lack of information will be formidable. At the same time, phylogenetic questions have become more tractable, and DNA sequence-based studies have resolved questions that earlier studies could not resolve, radically changing our understanding of the number of origins and losses of sociality in these bees.

New insights into the anatomy, systematics, and biogeography of centipedes have put these predatory terrestrial arthropods at the forefront of evolutionary studies. Centipedes have also played a pivotal role in understanding high-level arthropod relationships. Their deep evolutionary history, with a fossil record spanning 420 million years, explains their current worldwide distribution. Recent analyses of combined morphological and molecular data provide a stable phylogeny that underpins evolutionary interpretations of their biology. The centipede trunk, with its first pair of legs modified into a venom-delivering organ followed by 15 to 191 leg pairs, is a focus of arthropod segmentation studies. Gene expression studies and phylogenetics shed light on key questions in evolutionary developmental biology concerning the often group-specific fixed number of trunk segments, how some centipedes add segments after hatching whereas others hatch with the complete segment count, the addition of segments through evolution, and the invariably odd number of leg-bearing trunk segments.

Studies in Drosophila melanogaster have revealed paradigms for regulating gene expression through chromatin structure, including mechanisms of gene activation and silencing. Regulation occurs at the level of individual genes, chromosomal domains, and entire chromosomes. The chromatin state is dynamic, allowing for changes in gene expression in response to cellular signals and/or environmental cues. Changes in chromatin result from the action of ATP-dependent chromatin-remodeling complexes, reversible epigenetic histone modifications, and the incorporation of histone variants. Many of the chromatin-based transcriptional regulatory mechanisms discovered in D. melanogaster are evolutionarily conserved and therefore serve as a foundation for studies in other organisms.

Dichotomous keys that follow a single pathway of character state choices to an end point have been the primary tools for the identification of unknown organisms for more than two centuries. However, a revolution in computer diagnostics is now under way that may result in the replacement of traditional keys by matrix-based computer interactive keys that have many paths to a correct identification and make extensive use of hypertext to link to images, glossaries, and other support material. Progress is also being made on replacing keys entirely by optical matching of specimens to digital databases and DNA sequences. These new tools may go some way toward alleviating the taxonomic impediment to biodiversity studies and other ecological and evolutionary research, especially with better coordination between those who produce keys and those who use them and by integrating interactive keys into larger biological Web sites.

Yellow fever virus (YFV) is the prototype member of the genus Flavivirus, a group of viruses that are transmitted between vertebrates by arthropod vectors. The virus is found in tropical regions of Africa and South America and is transmitted to primates by mosquitoes: Aedes spp. in Africa and Haemagogus and Sabethes spp. in South America. Despite the availability of an effective vaccine, yellow fever (YF) is considered a reemerging disease owing to its increased incidence in the past 25 years. Molecular epidemiologic data suggest there are seven genotypes of YFV that are geographically separated, and outbreaks of disease are more associated with particular genotypes. In addition, the risk of urban YF, owing to transmission of the virus by Aedes aegypti, is increasing in Africa, as is the potential of urban YF returning to South America. Both present serious potential public health problems to large population centers.

Xenobiotic resistance in insects has evolved predominantly by increasing the metabolic capability of detoxificative systems and/or reducing xenobiotic target site sensitivity. In contrast to the limited range of nucleotide changes that lead to target site insensitivity, many molecular mechanisms lead to enhancements in xenobiotic metabolism. The genomic changes that lead to amplification, overexpression, and coding sequence variation in the three major groups of genes encoding metabolic enzymes, i.e., cytochrome P450 monooxygenases (P450s), esterases, and glutathione-S-transferases (GSTs), are the focus of this review. A substantial number of the adaptive genomic changes associated with insecticide resistance that have been characterized to date are transposon mediated. Several lines of evidence suggest that P450 genes involved in insecticide resistance, and perhaps insecticide detoxification genes in general, may share an evolutionary association with genes involved in allelochemical metabolism. Differences in the selective regime imposed by allelochemicals and insecticides may account for the relative importance of regulatory or structural mutations in conferring resistance.

The choice of a new nest site is ecologically critical for an insect colony. In swarm-founding social insects, or those that move as colonies from one site to another, this choice is one of the best-available examples of a distributed, nonhierarchical decision-making process in animals. In the few species of ants and bees that have been studied in detail, the main features of this collective decision making are strikingly similar, although some differences occur. Individual scouts discover potential nest sites and integrate multiple properties of these sites into assessments of their quality. The discovered sites then compete for a limited pool of nest-site scouts, and attrition of less-favored sites occurs by several mechanisms. Finally, the mass movement of the colony to the new site is triggered by a quorum-sensing mechanism when sufficient scouts are present at one of the alternatives. Movement itself is coordinated by different mechanisms in different insects.

Allatostatins are pleiotropic neuropeptides for which one function in insects is the inhibition of juvenile hormone synthesis. Juvenile hormone, an important regulator of development and reproduction in insects, is produced by the corpora allata. Mandibular organs, the crustacean homologs of insect corpora allata, produce precursors of juvenile hormone with putatively similar functions. Three types of allatostatins in insects have been isolated: FGLamides, W(X)6Wamides, and PISCFs. All act rapidly and reversibly; however, although these types occur in all groups of insects studied, they act as inhibitors of juvenile hormone production in only some groups. Only the FGLamide-type peptides have been isolated in crustaceans, in which they may function to stimulate production of hormone by the mandibular glands, as occurs in early cockroach embryos. Much remains to be learned in order to understand the role of allatostatins in the modulation of hormone production.

Among herbivorous insects with a complete metamorphosis the larval and adult stages usually differ considerably in their nutritional requirements and food ecology. Often, feeding on plant structural tissue is restricted to the larval stage, whereas the adult stage feeds primarily or exclusively on plant-provided food supplements such as nectar and pollen. Research on herbivore nutritional ecology has largely been divided along these lines. Most studies focus on actual herbivory by larval stages, while nectar and pollen feeding by adult herbivores has been addressed mainly in the light of plant-pollinator interactions. Only recently have we started to realize that the two phenomena are closely interlinked and that nectar and pollen feeding by adult herbivores can have a strong impact on plant-herbivore interactions. Here we address this largely ignored aspect of multitrophic level interactions and discuss its wide-ranging implications.

The Adelgidae form a small clade of insects within the Aphidoidea (Hemiptera) that includes some of the most destructive introduced pest species threatening North American forest ecosystems. Despite their importance, little is known about their evolutionary history and their taxonomy remains unresolved. Adelgids are cyclically parthenogenetic and exhibit multigeneration complex life cycles. They can be holocyclic, with a sexual generation and host alternation, or anholocyclic, entirely asexual and without host alternation. We discuss adelgid behavior and ecology, emphasizing plant-insect interactions, and we explore ways that the biogeographic history of their host plants may have affected adelgid phylogeny and evolution of adelgid life cycles. Finally, we highlight several areas in which additional research into speciation, population genetics, multitrophic interactions, and life-history evolution would improve our understanding of adelgid biology and evolution.

The cimicids, or bed bugs, belong to a highly specialized hematophagous taxon that parasitizes primarily humans, birds, and bats. Their best-known member is the bed bug, Cimex lectularius. This group demonstrates some bizarre but evolutionarily important biology. All members of the family Cimicidae show traumatic insemination and a suite of female adaptations to this male trait. Cimicids therefore constitute an ideal model system for examining the extreme causes and consequences of sexual selection. Our dual goal in re-examining the extensive literature on this group is to identify issues relevant to pest control, such as dispersal ecology and the recent global spread, and to understand the selective forces that have shaped the unique aspects of this insect's biology.

Push-pull strategies involve the behavioral manipulation of insect pests and their natural enemies via the integration of stimuli that act to make the protected resource unattractive or unsuitable to the pests (push) while luring them toward an attractive source (pull) from where the pests are subsequently removed. The push and pull components are generally nontoxic. Therefore, the strategies are usually integrated with methods for population reduction, preferably biological control. Push-pull strategies maximize efficacy of behavior-manipulating stimuli through the additive and synergistic effects of integrating their use. By orchestrating a predictable distribution of pests, efficiency of population-reducing components can also be increased. The strategy is a useful tool for integrated pest management programs reducing pesticide input. We describe the principles of the strategy, list the potential components, and present case studies reviewing work on the development and use of push-pull strategies in each of the major areas of pest control.

The arthropod class Diplopoda, the millipedes, ranks among the most diverse groups of terrestrial organisms, with over 12,000 species described. Although they play an important ecological role in most terrestrial ecosystems, little is known about the group's diversity, morphology, and phylogeny compared with other arthropod groups. We review diplopod natural history and discuss the historical and current literature pertaining to millipede morphology, ecology, chemical defenses, and the paleontological record of the group's ancient history. Diplopod systematics, past and present, are reviewed with a focus on taxonomy, collections, and biogeography. The phylogenetics of the class is reviewed, with particular attention on diplopod placement within the Myriapoda and emphasis on recent advances using molecular approaches to phylogenetic reconstruction. We present (a) the first combined morphological and molecular analysis of the millipede orders, and (b) a list of critically evaluated characteristics of nominal clades identifying putative apomorphies.