Showing papers in "Annual Review of Entomology in 1998"

Sustainability of Transgenic Insecticidal Cultivars: Integrating Pest Genetics and Ecology

Abstract: ▪ Abstract This review examines potential impacts of transgenic cultivars on insect population dynamics and evolution. Experience with classically bred, insecticidal cultivars has demonstrated that a solid understanding of both the target insect's ecology and the cultivar's performance under varied field conditions will be essential for predicting area-wide effects of transgenic cultivars on pest and natural enemy dynamics. This experience has also demonstrated the evolutionary capacity of pests for adaptive response to insecticidal traits in crops. Biochemical and genetic studies of insect adaptation to the Bacillus thuringiensis (Bt) toxins expressed by currently marketed transgenic cultivars indicate a high risk for rapid adaptation if these cultivars are misused. Theoretical and practical issues involved in implementing strategies to delay pest adaptation to insecticidal cultivars are reviewed. Emphasis is placed on examining the “high dose”/refuge strategy that has become the goal of industry and reg...

Nutritional Interactions in Insect-Microbial Symbioses: Aphids and Their Symbiotic Bacteria Buchnera

Abstract: Most aphids possess intracellular bacteria of the genus Buchnera. The bacteria are transmitted vertically via the aphid ovary, and the association is obligate for both partners: Bacteria-free aphids grow poorly and produce few or no offspring, and Buchnera are both unknown apart from aphids and apparently unculturable. The symbiosis has a nutritional basis. Specifically, bacterial provisioning of essential amino acids has been demonstrated. Nitrogen recycling, however, is not quantitatively important to the nutrition of aphid species studied, and there is strong evidence against bacterial involvement in the lipid and sterol nutrition of aphids. Buchnera have been implicated in various non-nutritional functions. Of these, just one has strong experimental support: promotion of aphid transmission of circulative viruses. It is argued that strong parallels may exist between the nutritional interactions (including the underlying mechanisms) in the aphid-Buchnera association and other insect symbioses with intracellular microorganisms.

Integrated pest management: historical perspectives and contemporary developments.

Abstract: Twenty five years after its first enunciation, IPM is recognized as one of the most robust constructs to arise in the agricultural sciences during the second half of the twentieth century. The history of IPM, however, can be traced back to the late 1800s when ecology was identified as the foundation for scientific plant protection. That history, since the advent of modern organosynthetic pesticides, acquired elements of drama, intrigue, jealousy, and controversy that mark the path of many great scientific or technological achievements. Evolution of IPM followed multiple paths in several countries and reached beyond the confines of entomological sciences. Time and space constraints, however, bias this review toward entomology, among the plant protection sciences, and give it an obvious US slant, despite the global impact of IPM.

Biological control of weeds

Abstract: Classical biological control, i.e. the introduction and release of exotic insects, mites, or pathogens to give permanent control, is the predominant method in weed biocontrol. Inundative releases of predators and integrated pest management are less widely used. The United States, Australia, South Africa, Canada, and New Zealand use biocontrol the most. Weeds in natural ecosystems are increasingly becoming targets for biocontrol. Discussion continues on agent selection, but host-specificity testing is well developed and reliable. Post-release evaluation of impact is increasing, both on the target weed and on non-target plants. Control of aquatic weeds has been a notable success. Alien plant problems are increasing worldwide, and biocontrol offers the only safe, economic, and environmentally sustainable solution.

Plasticity in Life-History Traits

Abstract: We describe the impact of recent life-history plasticity theory on insect studies, particularly on the interface between genetics and plasticity. We focus on the three-dimensional relationship between three key life-history traits: adult size (or mass), development time and growth rate, and the connections to life cycle regulation, host plant choice, and sexual selection in seasonal environments. The review covers fitness consequences of variation in size, development time and growth rate, and effects of sex, photoperiod, temperature, diet, and perceived mortality risk on these traits. We give special attention to evidence for adaptive plasticity in growth rates because of the important effects of such plasticity on the expected relationships between development time and adult size and, hence, on the use of life-history, fitness, and optimality approaches in ecology, as well as in genetics.

New insecticides with ecdysteroidal and juvenile hormone activity.

Abstract: Agrochemical research over the last two decades has resulted in the discovery of chemically novel insecticides that mimic the action of the two insect growth and developmental hormones, the steroidal 20-hydroxyecdysone (20E) and the sesquiterpenoid juvenile hormone (JH). Bisacylhydrazines are non-steroidal agonists of 20E and exhibit their insecticidal activity via interaction with the ecdysteroid receptor proteins. Interestingly, two of the bisacylhydrazine (tebufenozide and RH-2485) insecticides are very selectively toxic to lepidopteran pests. These insecticides are safe to beneficial insects and have a benign ecotoxicological profile. Aromatic non-terpenoidal insecticides (fenoxycarb and pyriproxyfen) mimic the action of JHs. However, like the JHs, their exact mode of action is not well understood. These insecticides are toxic to a broad spectrum of insects during their embryonic, last larval, or reproductive stages. The insecticidal, ecotoxicological properties and the mode of action of the two groups of insecticides are reviewed in this article.

Golden age of insecticide research: past, present, or future?

Abstract: Insecticide research led to the first "complete" victories in combatting pests almost 50 years ago with the chlorinated hydrocarbons followed quickly by the organophosphates, methylcarbamates, and pyrethroids--all neuroactive chemicals. This Golden Age of Discovery was the source of most of our current insecticides. The challenge then became health and the environment, a Golden Age met with selective and degradable compounds. Next the focus shifted to resistance, novel biochemical targets, and new chemical approaches for pest control. The current Golden Age of Genetic Engineering has curtailed, but is unlikely to eliminate, chemical use on major crops. Insecticide research, having passed through several Golden Ages, is now in a renaissance of integrating chemicals and biologicals for sustainable pest control with human safety.

Biodiversity of stream insects: variation at local, basin, and regional scales.

Abstract: ▪ Abstract We review the major conceptual developments that have occurred over the last 50 years concerning the factors that influence insect biodiversity in streams and examine how well empirical descriptions and theory match. Stream insects appear to respond to both spatial and temporal variation in physical heterogeneity. At all spatial scales, the data largely support the idea that physical complexity promotes biological richness, although exceptions to this relationship were found. These exceptions may be related to how we measure habitat complexity at finer spatial scales and to factors that influence regional richness, such as biogeographic history, at broader spatial scales. However, the degree to which local stream insect assemblages are influenced by regional processes is largely unknown.

The ecology and behavior of burying beetles

Abstract: Burying beetles conceal small vertebrate carcasses underground and prepare them for consumption by their young. This review places their complex social behavior in an ecological context that focuses on the evolution of biparental care and communal breeding. Both males and females provide extensive parental care, and the major benefit of male assistance is to help defend the brood and carcass from competitors. As intensity and type of competition vary, so do the effectiveness and duration of male care. In many species, a single brood may be reared on large carcasses by more than one male and/or female. Limited reproductive opportunities, the greater effectiveness of groups in preventing the probability of brood failure (especially that caused by competing flies), and the superabundance of food on large carcasses have contributed to the evolution of this cooperative behavior.

Predaceous Coccinellidae in biological control.

Abstract: Coccinellids have been widely used in biological control for over a century, and the methods for using these predators have remained virtually unchanged. The causes for the relatively low rates of establishment of coccinellids in importation biological control have not been examined for most species. Augmentative releases of several coccinellid species are well documented and effective; however, ineffective species continue to be used because of ease of collection. For most agricultural systems, conservation techniques for coccinellids are lacking, even though they are abundant in these habitats. Evaluation techniques are available, but quantitative assessments of the efficacy of coccinellids have not been done for most species in most agricultural crops. Greater emphasis is needed on evaluation, predator specificity, understanding colonization of new environments, and assessment of community-level interactions to maximize the use of coccinellids in biological control.

Higher-order predators and the regulation of insect herbivore populations

Abstract: ▪ Abstract Empirical research has not supported the prediction that populations of terrestrial herbivorous arthropods are regulated solely by their natural enemies. Instead, both natural enemies (top-down effects) and resources (bottom-up effects) may play important regulatory roles. This review evaluates the hypothesis that higher-order predators may constrain the top-down control of herbivore populations. Natural enemies of herbivorous arthropods generally are not top predators within terrestrial food webs. Insect pathogens and entomopathogenic nematodes inhabiting the soil may be attacked by diverse micro- and mesofauna. Predatory and parasitic insects are attacked by their own suite of predators, parasitoids, and pathogens. The view of natural enemy ecology that has emerged from laboratory studies, where natural enemies are often isolated from all elements of the biotic community except for their hosts or prey, may be an unreliable guide to field dynamics. Experimental work suggests that interactions ...

Insect performance on experimentally stressed woody plants: a meta-analysis.

Abstract: In this review, we test the hypothesis that abiotic stress increases the suitability of plants as food for herbivores. We conducted a meta-analysis that included 70 experimental studies in which insect performance was measured on woody plants subjected to water stress, pollution, and/or shading. Overall, plant stress had no significant effect on insect growth rate, fecundity, survival, or colonization density. We found great variation, however, in the magnitude and direction of insect responses among studies, most of which was related to insect feeding guild. In general, boring and sucking insects performed better on stressed plants, whereas plant stress adversely affected gall-makers and chewing insects. Reduction in performance of chewers was greater on stressed slow-growing plants than on stressed fast growers. Reproductive potential of sucking insects was increased by pollution but reduced by water stress. In some cases where sample sizes were small or the treatment periods short, apparent differences in insect responses to stress were probably artifacts due to inappropriate experimental design.

Fire and insects in northern and boreal forest ecosystems of North America.

Abstract: ▪ Abstract Fire and insects are natural disturbance agents in many forest ecosystems, often interacting to affect succession, nutrient cycling, and forest species composition. We review literature pertaining to effects of fire-insect interactions on ecological succession, use of prescribed fire for insect pest control, and effects of fire on insect diversity from northern and boreal forests in North America. Fire suppression policies implemented in the early 1900s have resulted in profound changes in forest species composition and structure. Associated with these changes was an increased vulnerability of forest stands to damage during outbreaks of defoliating insects. Information about the roles that both fire and insects play in many northern forests is needed to increase our understanding of the ecology of these systems and to develop sound management policies.

Malaria parasite development in mosquitoes

Abstract: Mosquitoes of the genus Anopheles transmit malaria parasites to humans. Anopheles mosquito species vary in their vector potential because of environmental conditions and factors affecting their abundance, blood-feeding behavior, survival, and ability to support malaria parasite development. In the complex life cycle of the parasite in female mosquitoes, a process termed sporogony, mosquitoes acquire gametocyte-stage parasites from blood-feeding on an infected host. The parasites carry out fertilization in the midgut, transform to ookinetes, then oocysts, which produce sporozoites. Sporozoites invade the salivary glands and are transmitted when the mosquito feeds on another host. Most individual mosquitoes that ingest gametocytes do not support development to the sporozoite stage. Bottle-necks occur at every stage of the cycle in the mosquito. Powerful new techniques and approaches exist for evaluating malaria parasite development and for identifying mechanisms regulating malaria parasite-vector interactions. This review focuses on those interactions that are important for the development of new approaches for evaluating and blocking transmission in nature.

Manipulating Natural Enemies By Plant Variety Selection and Modification: A Realistic Strategy?

Abstract: ▪ Abstract The host plants of arthropod pests may affect parasitoids and predators directly or indirectly, through multitrophic interactions. Direct plant effects may involve simple mechanisms such as reduced parasitoid searching efficiency caused by trichomes. Multitrophic effects often involve complex interactions that are not well understood, and their impact on natural enemies and biological control are difficult to predict. Knowledge of the direct and multitrophic effects creates opportunities to increase the effectiveness of natural enemies by incorporating natural enemy–enhancing traits into crop plants. The strategy may have potential for both generalist and specialist natural enemies, but the enemies' behavior and other factors will affect the results. Although combining natural enemies and plant resistance may slow the adaptation of some insect pests, it may speed up adaptations of others. A better understanding of plant/pest/natural enemy evolution is necessary to predict how to combine natural...

Eradication and pest management

Abstract: Eradication is the elimination of every single individual of a species from an area to which recolonization is unlikely to occur. Cost-benefit analyses of eradication programs involve biases that tend to underestimate the costs and overestimate the benefits. In this review, we (a) highlight limitations of current cost-benefit analyses, (b) assess eradication strategies from biological and sociological perspectives by discussing particular cases of successful and failed eradication efforts, and ( c) briefly contrast eradication and ongoing area-wide control as pest management strategies. Two successful eradication programs involve the screwworm and cattle ticks. Gypsy moth and medfly eradication programs have not been successful, and subsequent captures of insects recur in eradication areas. In situations where heterogeneity of land use patterns make it difficult to prevent reinvasion of the pest, education and area-wide suppression are probably more realistic goals than eradication.

Evolution and ecology of spider coloration

Abstract: Genetic color variation provides a tangible link between the external phenotype of an organism and its underlying genetic determination and thus furnishes a tractable system with which to explore fundamental evolutionary phenomena. Here we examine the basis of color variation in spiders and its evolutionary and ecological implications. Reversible color changes, resulting from several mechanisms, are surprisingly widespread in the group and must be distinguished from true genetic variation for color to be used as an evolutionary tool. Genetic polymorphism occurs in a large number of families and is frequently sex limited: Sex linkage has not yet been demonstrated, nor have the forces promoting sex limitation been elucidated. It is argued that the production of color is metabolically costly and is principally maintained by the action of sight-hunting predators. Key avenues for future research are suggested.

Reproductive caste determination in eusocial wasps (Hymenoptera: Vespidae).

Abstract: Wasps (Vespidae) exhibit a range of social complexity, from solitary living to eusocial colonies, and thus are exemplary for studies of the evolutionary origin and maintenance of social behavior in animals. Integral to the definition of eusociality is the presence of reproductive castes, group members that differ qualitatively in their ability to reproduce in a social setting. Behavioral and morphological evidence suggests that caste determination, the developmental process by which differences in fecundity are established, occurs to a large extent before adult emergence (pre-imaginally) in many species of Vespidae, in both basal and advanced taxa within the clade (Vespinae+Polistinae), which includes most eusocial species. Pre-imaginal determination has been documented in many taxa (e.g. independent-founding Polistinae) where it was not thought to occur. Correlative and experimental studies indicate that differences in nutrition during larval development are often the basis of pre-imaginal caste determination. Pre-imaginal caste determination has important implications for the roles of subfertility and manipulation by nest mates in the evolution of eusocial behavior.

Biology and use of the whitefly parasitoid encarsia formosa

Abstract: ▪ Abstract Encarsia formosa is a parasitoid used worldwide for the biological control of whiteflies on vegetables and ornamental plants grown in greenhouses. Because of outstanding success in controlling Trialeurodes vaporariorum on tomatoes, the biology and behavior of this wasp have been intensively studied to identify attributes that contribute to successful biological control and how best to manipulate augmentative releases into greenhouses to suppress whitefly population growth. In this article, we review the biology of adult and immature E. formosa, population dynamics of whitefly-parasitoid interactions, and commercial use in greenhouses. Deficits in knowledge of aspects of E. formosa's biology and use are noted.

Phylogeny and evolution of host-parasitoid interactions in hymenoptera.

Abstract: ▪ Abstract Recent studies of hymenopteran phylogeny using both comparative morphology and DNA sequence data have greatly enhanced our understanding of the evolution of that order. Resulting phylogenetic hypotheses make possible more rigorous investigations of the evolution of various biological life-styles, among them the parasitoid habit. This paper reviews the current findings from higher-taxon phylogenetic analyses of the order. A “consensus” phylogeny derived from these findings is used to trace the most likely evolutionary pathways leading to the current diversity of parasitoid habits. Taxa and biological phenomena for which our current understanding is fragmentary are highlighted. Based on current evidence, it appears that parasitism arose, from mycophagous ancestors, a single time within the order. Many subsequent elaborations of the parasitic mode of life (e.g. endoparasitism, secondary phytophagy, etc) apparently evolved independently more than once.

Life on the edge: insect ecology in arctic environments.

Abstract: ▪ Abstract The restricted Arctic insect fauna is usually explained by a lack of recolonization since the last glacial period, inadequate supply of suitable resources, or insufficient adaptation to such a harsh environment. These hypotheses and others that attempt to explain the latitudinal gradient of species distributions and abundance are reviewed. Arctic habitats available to insects are strongly heterogeneous, requiring a similarly diverse array of adaptive responses, characteristic of those species that have colonized and survived in such a stressful climate. Important adaptations in morphology (size, wings), behavior (activity patterns, thermoregulation), life cycles, and ecophysiology (cold hardiness, anaerobiosis, desiccation resistance) are discussed. The current focus of global climate change research on polar regions is identifed, particularly the opportunity to study fundamental ecological processes and spatial dynamics in the relatively simple Arctic ecosystems.

Chemical ecology of phytophagous scarab beetles

Abstract: ▪ Abstract Sex pheromones have been characterized only for species in the subfamilies Rutelinae and Melolonthinae; aggregation pheromones have been identified for two species in the Dynastinae. Melolonthines utilize mainly amino acid derivatives and terpenoid compounds, but sex pheromones of rutelines are fatty acid derivatives. Various other species utilize japonilure-type lactones that are produced by desaturation of fatty acids, followed by hydroxylation, chain shortening, and cyclization. In marked contrast to melolonthine sex pheromone glands that are everted from the abdominal tip, ruteline sex pheromone glands consist of epithelial cells that line the inner surfaces of the pygidium and two apical sternites. Some species that are geographically and/or seasonally isolated utilize the same sex pheromone system, but chirality plays an important role in the isolation of the communication channels of two ruteline species, where one enantiomer is utilized as sex pheromone and the other is a behavioral ant...

Spatial heterogeneity and insect adaptation to toxins

Abstract: Behavioral responses of insect herbivores to toxins are examined in managed and natural systems with reference to two important but largely ignored factors: heterogeneity in toxin distributions and the nature of the relationship between behavioral responses and physiological adaptation to the same toxins. Heterogeneous toxin distributions, which provide the opportunity for behavioral responses, are ubiquitous in managed and natural systems. Insect herbivores have evolved a wide variety of behavioral responses to such toxins. The nature of behavioral responses reflects toxin apparency, mode of action, and the extent to which sublethal effects influence behavior. The interaction between these behavioral responses to heterogeneously distributed toxins and physiological mechanisms of tolerance has influenced the evolution of insecticide resistance in managed systems and the evolution of plant defensive strategies in natural systems. An understanding of this interaction could lead to more evolutionarily stable methods of crop protection.

Indirect sperm transfer in arthropods: behavioral and evolutionary trends.

Abstract: Arachnids, myriapods, and wingless hexapods exhibit a fascinating diversity of sperm transfer behaviors. Modes of sperm transfer can be categorized by the degree of contact between male and female during transfer, with direct transfer (copulation) involving the greatest contact, paired-indirect transfer an intermediate degree, and dissociated transfer the least. Internal fertilization, spermatophores, and copulation are sometimes assumed to have evolved after invasion of land, but all have evolved many times in the marine habitat. Behaviors associated with indirect sperm transfer include those having close parallels with direct transfer (provision of nuptial gifts) as well as unique phenomena (spermatophore trampling by rival males). The morphology and physiology of indirectly transferred spermatophores have been shaped by environmental factors (e.g. humidity) as well as biological ones (e.g. clutch size of females), and they may provide useful phylogenetic characters. Unanswered questions about indirect transfer include the following: Are females of dissociated species able to choose their partners? What determines size and number of spermatophores? Do speciation rates differ between taxa with direct versus indirect transfer?

Parasites and pathogens of mites

Abstract: Mites are an ancient group of arachnids that have had some 400 million years to adapt to a variety of conditions on Earth. Microorganisms have had the same amount of time to form symbiotic relationships with mites, with results ranging from phoresy to parasitism. This review covers the still fragmentary information on the groups of parasites and pathogens that are associated with mites. The known mite-associated bacteria, rickettsiae, fungi, Protozoa, viruses, and nematodes represent the tip of the iceberg, and few details of their host-parasite relationships have been recorded. Mites offer an opportunity to investigate new pathogens and new types of associations. Pathogens can be a boon when they affect mites that are detrimental to crops, livestock, or ourselves, and the diseases they cause probably play an important role in controlling mites, at least under certain conditions. However, pathogens can also cause crop failure and economic loss when they occur in biological control agents of pests.

The Biology of Nonfrugivorous Tephritid Fruit Flies

Abstract: This review is the first comprehensive treatment of the biology of nonfrugivorous fruit flies of the family Tephritidae. Feeding habits of destructive and useful species, morphology of immature stages, and hypotheses regarding structural homology and the evolutionary biology of nonfrugivorous tephritids are reviewed, including zoogeography and theories involving resource heterogeneity, guild structure, resource partitioning, resource utilization, facultative niche exploitation, extrinsic and intrinsic factors, host associations, seasonal distribution and phenology, aggregative and circumnatal life history strategies, voltinism, diapause, aestivation, oviposition site, clutch size, and supernumerary oviposition.

Ecology and management of hazelnut pests

Abstract: ▪ Abstract Insect and mite pests cause serious damage to the hazelnut crop worldwide. The control strategies used against these pests include application of insecticides, classical and augmentative biological control, utilization of resistant varieties, and use of Bacillus thuringiensis–based preparations. In the United States, extensive research has been directed toward elucidating ecological interactions among different pests and natural enemies and understanding the role of abiotic factors in pest population dynamics. Differences exist worldwide regarding the understanding of pests and natural enemy biologies and, to a limited extent, control practices. An integrated pest management approach based on utilizing effective sampling and monitoring techniques and a near complete reliance on biological control and “soft” pesticides, including insect growth regulators, is currently under development both in North America and Europe/Turkey. Hazelnuts are on the verge of becoming one of the first crops in the U...

Ecological considerations for the environmental impact evaluation of recombinant baculovirus insecticides.

Abstract: ▪ Abstract The history of baculoviruses in insect control and the current status of recombinant baculovirus (recBV) insecticides in the laboratory and the field are briefly outlined. A conceptual model for impact evaluation is described that distinguishes between scientific impact evaluation and regulatory risk assessment. Its components are identified and reviewed in the light of existing ecological theory and experimental study under the categories of impact identification, exposure identification, and impact evaluation. Impact identification aims to identify species and populations sensitive to direct or indirect impacts by a recBV. Exposure identification examines how susceptible populations may be exposed to a recBV. Impact evaluation combines these data to predict the potential for recBV impacts in the environment.

Biology of the Mantispidae.

Abstract: ▪ Abstract Members of the Neuropteran family Mantispidae, subfamily Mantispinae, are predators in the egg sacs of spiders, draining egg contents through a piercing/sucking tube formed by modified mandibles and maxillae. First-instar mantispids use two strategies to locate spider eggs: Larvae may burrow directly through the silk of egg sacs they find, or they may board and be carried by female spiders prior to sac production, entering the sac as it is being constructed. Mantispids that board spiders usually adopt positions on or near the pedicel; some species may enter the spider's book lungs. Larvae maintain themselves aboard spiders by feeding on spider blood. Transfers of larvae from spider to spider are possible during spider mating or cannibalism. All of the major groups of hunting spiders are attacked by spider-boarding mantispids; the egg sacs of web-building species are also entered by egg-sac penetrators.

Differential gene expression in insects: Transcriptional control

Abstract: Studies on transcriptional control of gene expression play a pivotal role in many areas of biology. In non-Drosophilid insects, the cuticle, chorion, immune response, silk gland, storage proteins, and vitellogenin are foci for advances in basic research on promoter elements and transcription factors. Insects offer other advantages for gene regulation studies, including the availability of applied problems. In non-Drosophilid insects, the most serious problem for transcriptional control studies is the lack of homologous in vivo expression systems. Once this deficiency is addressed, the full impact of research on transcription control will be realized throughout the field of entomology.