Showing papers in "Annual Review of Entomology in 1996"

The role of macroinvertebrates in stream ecosystem function.

Abstract: This review focuses on some of the roles of macroinvertebrate functional groups, i.e. grazers, shredders, gatherers, filterers, and predators, in stream-ecosystem processes. Many stream-dwelling insects exploit the physical characteristics of streams to obtain their foods. As consumers at intermediate trophic levels, macroinvertebrates are influenced by both bottom-up and top-down forces in streams and serve as the conduits by which these effects are propagated. Macroinvertebrates can have can important influence on nutrient cycles, primary productivity, decomposition, and translocation of materials. Interactions among macroinvertebrates and their food resources vary among functional groups. Macroinvertebrates constitute an important source of food for numerous fish, and unless outside energy subsidies are greater than in-stream food resources for fish, effective fisheries management must account for fish-invertebrate linkages and macroinvertebrate linkages with resources and habitats. Macroinvertebrates also serve as valuable indicators of stream degradation. The many roles performed by stream-dwelling macroinvertebrates underscore the importance of their conservation.

Ecology and behavior of ground beetles (Coleoptera: Carabidae).

Abstract: The ground beetles form the speciose beetle family Carabidae and, since their emergence in the Tertiary, have populated all habitats except deserts. Our knowledge about carabids is biased toward species living in north-temperate regions. Most carabids are predatory, consume a wide range of food types, and experience food shortages in the field. Feeding on both plant and animal material and scavenging are probably more significant than currently acknowledged. The most important mortality sources are abiotic factors and predators; pathogens and parasites can be important for some developmental stages. Although competition among larvae and adults does occur, the importance of competition as a community organization is not proven. Carabids are abundant in agricultural fields all over the world and may be important natural enemies of agricultural pests.

Biological Control with Trichogramma: Advances, Successes, and Potential of Their Use

Abstract: Major contributions to the release of Trichogramma for biological control of lepidopterous pests have been made in the past 20 years. Most trials have used only five species of Trichogramma against two pests; Ostrinia in corn is considered the most universally feasible. All Trichogramma programs must address the following four aspects to be successful commercially. Selection of the appropriate population is based on inter- and intraspecific variation, as well as on current definitions of parasitoid quality. Mass rearing is comprised of both host and parasitoid components, although major emphasis is now on developing artificial systems. Effective distribution of Trichogramma requires supportive extension and advanced technology. Strategies for use in the field vary according to the approach desired (inundative or inoculative), the timing, frequency and rate of release, and the multiple factors that affect release, such as the weather, crop, host, predation, pesticides, and dispersal. The past difficulty in...

Ecology of Insect Communities in Nontidal Wetlands

Abstract: Published research about wetland insects has proliferated, and a conceptual foundation about how wetland insect populations and communities are regulated is being built. Here we review and synthesize this new body of work. Our review begins with a summary of insect communities found in diverse wetland types, including temporary pools, seasonally flooded marshes, perennially flooded marshes, forested floodplains, and peatlands. Next, we critically discuss research on the population and community ecology of wetland insects, including the importance of colonization strategies and insect interactions with the physical environment, plants, predators, and competitors. Results from many of the experimental studies that we review indicate that some commonly held beliefs about wetland insect ecology require significant reevaluation. We then discuss the importance of wetland insect ecology for some applied concerns such as efforts to manage wetland insect resources as waterfowl food and development of ecologically ...

The Role of Nourishment in Oogenesis

Abstract: Oogenesis in insects is typically a nutrient-limited process, triggered only if sufficient nourishment is available. This nourishment can be acquired during the larval or adult stage, depending on the insect. Timing of food intake will have major effects on mechanisms of hormonal control. When nourishment for eggs is taken primarily by adults, insufficient nutrition inhibits egg development through mechanisms such as inhibition of corpora allata, as seen in Orthoptera and Blattaria. In adult Diptera, lack of protein inhibits release of brain factors that produce reproductive competency or ovarian stimulation. Lepidoptera have been characterized as lacking substantial regulation of oogenesis because egg development is underway at emergence. Many species for which ecological data are available do not mobilize reserves carried over from the larval stage until they feed as adults. The endocrine mechanisms underlying these systems are poorly understood. In many insects, mating and activity can affect nutritional state and therefore oogenesis. Mating can stimulate oogenesis through mobilization of reserves or through nutritional contributions by males to females. Activity, especially flight, and oogenesis can compete for energy. The flight apparatus, especially the muscle, can also compete with oogenesis for protein. Social insects exhibit extreme specializations in oogenesis; females range in fertility from completely sterile to hyperfecund. Food flow within colonies is a major factor regulating fecundity. Finally, maternal nourishment is not needed for oogenesis in parasitoids and pseudoplacental viviparous insects, which produce eggs with little or no yolk. Virtually nothing is known about the endocrine regulation of oogenesis on these insects.

Ion Channels as Targets for Insecticides

Abstract: Ion channels are the primary target sites for several classes of natural and synthetic insecticidal compounds. The voltage-sensitive sodium channel is the major target site for DDT and pyrethroids, the veratrum alkaloids, andN-alkylamides. Recently, neurotoxic proteins from arthropod venoms, some of which specifically attack insect sodium channels, have been engineered into baculoviruses to act as biopesticides. The synthetic pyrazolines also primarily affect the sodium channel, although some members of this group target neuronal calcium channels as well. The ryanoids have also found use as insecticides, and these materials induce muscle contracture by irreversible activation of the calcium-release channel of the sarcoplasmic reticulum. The arylheterocycles (e.g. endosulfan and fipronil) are potent convulsants and insecticides that block the GABA-gated chloride channel. In contrast, the avermectins activate both ligand and voltage-gated chloride channels, which leads to paralysis. At field-use rates, a ne...

Host immunity to ticks.

Abstract: The tick-host-pathogen interface is characterized by complex immunological interactions. Tick feeding induces host immune regulatory and effector pathways involving antibodies, complement, antigen-presenting cells, T lymphocytes, and other bioactive molecules. Acquired resistance impairs tick engorgement, ova production, and viability. Tick countermeasures to host defenses reduce T-lymphocyte proliferation, elaboration of the TH1 cytokines interleukin-2 and interferon-γ, production of macrophage cytokines interleukin-1 and tumor necrosis factor, and antibody responses. The dynamic balance between acquired resistance and tick modulation of host immunity affects engorgement and pathogen transmission. A thorough understanding of acquired immunity to ticks is essential for rational development of antitick vaccines.

Geographic structure of insect populations: gene flow, phylogeography, and their uses.

Abstract: Geographic structure of populations is a fundamental component of ecology and evolution that combines both demographic and genetic processes, such as gene flow and migration, genetic drift, selection, and population extinction. Recent advances in both molecular biology and theory have revolutionized the field and have not only expanded the availability of data but also facilitated the accessibility and interpretation of current data. These new techniques allow analysis of genetic similarity among populations to be coupled with phylogeography and the distribution of genotypes within and among populations relative to the history of those genotypes. The numerous case studies described herein illustrate the growing impact of geographic structure on insect science, as well as the importance of insect model systems for understanding general concepts in ecology and evolution.

Floral resource utilization by solitary bees (Hymenoptera: Apoidea) and exploitation of their stored foods by natural enemies.

Abstract: Bees are phytophagous insects that exhibit recurrent ecological specializations related to factors generally different from those discussed for other phytophagous insects. Pollen specialists have undergone extensive radiations, and specialization is not a always a derived state. Floral host associations are conserved in some bee lineages. In others, various species specialize on different host plants that are phenotypically similar in presenting predictably abundant floral resources. The nesting of solitary bees in localized areas influences the intensity of interactions with enemies and competitors. Abiotic factors do not always explain the intraspecific variation in the spatial distribution of solitary bees. Foods stored by bees attract many natural enemies, which may shape diverse facets of nesting and foraging behavior. Parasitism has evolved repeatedly in some, but not all, bee lineages. Available evidence suggests that cleptoparasitic lineages are most speciose in temperate zones. Female parasites f...

Discontinuous gas exchange in insects

Abstract: Many insects exchange respiratory gases cyclically and discontinuously. A typical discontinuous gas exchange cycle (DGC) starts with a closed-spiracle (C) phase, during which little external gas exchange takes place, followed by a fluttering-spiracle (F) phase, which is usually dominated by diffusive oxygen uptake. The DGC is terminated by an open-spiracle (O) phase, during which accumulated CO2 escapes. This review critically examines the applicability of the DGC to insect gas exchange in general, discusses the primary mechanisms of gas exchange in the F and O phases, evaluates the widespread hypothesis that the DGC lowers respiratory water loss rates adaptively, and proposes new hypotheses concerning the evolutionary genesis of the DGC in insects and other tracheate arthropods.

Predatory behavior of jumping spiders.

Abstract: Salticids, the largest family of spiders, have unique eyes, acute vision, and elaborate vision-mediated predatory behavior, which is more pronounced than in any other spider group. Diverse predatory strategies have evolved, including araneophagy, aggressive mimicry, myrmicophagy, and prey-specific prey-catching behavior. Salticids are also distinctive for development of behavioral flexibility, including conditional predatory strategies, the use of trial-and-error to solve predatory problems, and the undertaking of detours to reach prey. Predatory behavior of araneophagic salticids has undergone local adaptation to local prey, and there is evidence of predator-prey coevolution. Trade-offs between mating and predatory strategies appear to be important in ant-mimicking and araneophagic species.

Evolution of Ticks

Abstract: Evolutionary patterns in ticks have traditionally been cast in terms of host associations. Largely untested assumptions of cospeciation and observations of current host associations are used to estimate the age of different taxa. Several recent phylogenetic studies of supraspecific relationships in ticks, based on both morphological and DNA-sequence data, allow the first rigorous testing of these assumptions. Reanalysis of patterns of tick-host associations suggests that the perception of host specificity in ticks may be an artifact of incomplete sampling. An analysis of tick-host and -habitat associations and biogeographical patterns, in the context of the newly derived phylogenies, suggests that much of the existing host-association patterns may be explained as artifacts of biogeography and ecological specificity.

Bacillus sphaericus toxins: molecular biology and mode of action.

Abstract: Bacillus sphaericus is a spore-forming aerobic bacterium, several strains of which are pathogenic for mosquito larvae. During sporulation, the most active strains produce a crystal toxin with a high degree of larvicidal activity. The toxin is composed of two proteins of 51.4 and 41.9 kDa, which are encoded by highly conserved chromosomal genes. After B. sphaericus is ingested, these proteins are released in the larva's midgut, and, in susceptible mosquito species, bind to a specific receptor present on midgut brush-border membranes. The resulting damages to the midgut cells leads to the mosquitoes' death. During vegetative growth, some B. sphaericus strains also synthesize mosquito larvicidal proteins of 100 and 30.8 kDa (Mtx toxins), the mode of action of which is still unknown. The mechanism of acquisition of the recessive mosquito resistance to the crystal toxin varies with selection conditions.

Living on leaves: mites, tomenta, and leaf domatia.

Abstract: Structures on the surfaces of leaves strongly affect phylloplane mites. Glandular trichomes defend against some plant parasites but can also mire predators. However, leaves with tomenta of nonglandular trichomes are often inhabited by large populations of predatory mites. Tufts of hairs and other minute structures in the vein axils are called leaf domatia. Comparative observations and experimental data demonstrate that leaves with domatia have enhanced levels of predatory mites. By accumulating predatory mites, leaf domatia act as a kind of constitutive defense against herbivores. Mites benefit from leaf domatia by securing a safe place for oviposition and molting. Like several other plant structures, leaf domatia are the manifestation of a long-term and mutually beneficial interaction between plants and arthropods.

Semiochemical parsimony in the Arthropoda.

Abstract: A wide variety of arthropods have adapted their own semiochemicals to subserve multiple functions in diverse contexts. Semiochemicals, the pheromones and allomones, have been detected in arthropod species in six orders, and it has been clearly established that these compounds are used with great parsimony. The versatility of these invertebrates in using these natural products for an incredible diversity of functions emphasizes the significance of semiochemicals in the evolutionary biology of Arthropoda. Multifunctional pheromones have proved to be especially characteristic of the queens of eusocial species. Compounds such as the queen substance of the honey bee, Apis mellifera, possess unrelated primer and releaser functions for the workers and act as a sex attractant for drones. Females of other hymenopterous species exploit the secretions of sting-associated glands as sex pheromones, whereas a variety of nonhymenopterous species have adapted components in diverse defensive secretions to function as sex pheromones. The alarm pheromones of many arthropods are also used as defensive allomones, activity inhibitors, cryptic alarm pheromones, aggregative attractants, robbing agents, digging agents, trail pheromones, and antimicrobial agents. Defensive allomones also possess some of these parsimonious roles; in addition, however, some of these compounds possess highly distinctive roles, such as functioning as lethal attractants for prey, or, in he aquatic milieu, cuticular wetting agents. Clearly, the availability of a variety of pheromones and allomones has enabled arthropods to evolve an elegant semiochemical parsimony with which to exploit the biological milieu.

Development of Recombinant Baculoviruses for Insect Control

Abstract: In this review, we provide an overview of the current status of recombinant baculoviruses, describe the development of genetically engineered baculoviruses for use as rapid-action biological insecticides, and provide more detailed information on one particular set of recombinant viruses. The advantages and disadvantages of recombinant baculovirus insecticides, and the importance of risk-assessment studies of these genetically modified organisms, are reviewed. Finally the importance of sensible regulatory strategies to the success and future prospects of this technology is discussed.

Tympanal hearing in insects.

Abstract: Specialized hearing organs, known as tympanal organs, have evolved in at least seven different orders of insects. Tympanal organs are usually defined by the presence of a tympanal membrane (or eardrum). They are backed by an air-filled space or cavity and are innervated by a chordotonal sensory organ. In some insects, however, a recognizable tympanal membrane may not be easily identified by visual inspection, yet may possess tympanal hearing organs. In insects that possess them, tympanal hearing organs may mediate the detection of predators, prey, and potential mates and rivals. Unlike the ears of vertebrates, which are localized to cranial segments, the ears of insects may be found in a bewildering variety of locations on their bodies, depending on the species. The embryological and evolutionary origins of tympanal organs are related to ancestral states as proprioceptive chordotonal organs.

Culicoides Variipennis and Bluetongue-Virus Epidemiology in the United States

Abstract: The bluetongue viruses are transmitted to ruminants in North America by Culicoides variipennis. US annual losses of approximately $125 million are due to restrictions on the movement of livestock and germplasm to bluetongue-free countries. Bluetongue is the most economically important arthropod-borne animal disease in the United States. Bluetongue is absent in the northeastern United States because of the inefficient vector ability there of C. variipennis for bluetongue. The vector of bluetongue virus elsewhere in the United States is C. variipennis sonorensis. The three C. variipennis subspecies differ in vector competence for bluetongue virus in the laboratory. Understanding C. variipennis genetic variation controlling bluetongue transmission will help identify geographic regions at risk for bluetongue and provide opportunities to prevent virus transmission. Information on C. variipennis and bluetongue epidemiology will improve trade and provide information to protect US livestock from domestic and foreign arthropod-borne pathogens.

Insect Pests of Beans in Africa: Their Ecology and Management

Abstract: Damage by insect pests, inter alia, is considered the liming factor of bean praduction in Africa. This paper reviews the current status of insect pests of beans, focusing on their ecology and management, as well as the potential for integrated pest management (IPM) approaches in subsistence farming conditions, under which most beans are grown in Africa. Although numerous insect pests attacked parts of beans, bean stem maggots and bruchids are the most important field and storage pests, respectively. Foliage beetles, flower thrips, pollen beetles, pod borers, pod bugs, and sap suckers such as aphids also inflict signifcant damage. Control of bean pests in Africa is achieved through the use of a traditional IPM approach that consists of appropriate sowing dates, optimum plant density, varietal mixtures, intercropping, good crop husbandry, and locally available materials. Research should focus on low-input IPM approaches that encompass farmers’ current practices, host-plant resistance, and natural biological...

Sexual receptivity in insects.

Abstract: Sexual receptivity is female behavior that allows or helps a male to fertilize her eggs; through this behavior, females play an active role in reproduction. Multiple signals may be used for receptivity or unreceptivity. Insect species exhibit three ontogenetic patterns of receptivity: cyclic, in which females alternately become receptive and unreceptive; brief, in which females mate during on short developmental period; and continuous. Primary (initial) receptivity may be stimulated or inhibited by diet, ovarian development, or juvenile hormone. In species with cyclic receptivity, remating may be inhibited by copulation itself, the presence of eggs, sperm stored in spermathecae, or seminal factors--usually peptides--secreted by the male accessory glands. In many species, there is substantial genetic variation for both primary receptivity and speed of remating. Several single-gene mutations reduce female receptivity; most of these mutations also impair sensory functioning.

Sexual selection in relation to pest-management strategies.

Abstract: The application of principles derived from the sexual selection literature can assist attempts to subvert the normal mating behavior of pests. Sexual selection encompasses both intermale competition for access to females and female choice of mates. It can operate during long-range attraction and short-range courtship, as well as after copulation. We review the major aspects of sexual selection and illustrate their application to pheromonal and SIT pest-management programs. Pheromones are important both in long-range attraction and in close-range mate choice; parapheromones may be very useful in pest management because of their influence on male mating success. Sexual selection theory provides a scheme for studying the normal mating behavior of a pest species and thus determining which attributes of the mass-reared sterile males are critical to their success with wild females. We hope that our review will suggest novel ways of attacking pests as well as encourage behavioral ecologists to study pest species.