Annual Review of Entomology - Volume 40, 1995

The insect immune system serves as a key defense against attack by parasitoids. Incompatible hosts often eliminate parasitoids by encapsulation, a process in which hemocytes form a multilayered envelope around the invading organism. Capsule formation involves cooperation between one or more classes of hemocytes and is likely mediated by cytokines and adhesion molecules. Reciprocally, parasitoids have evolved a variety of strategies for overcoming host immune responses. Some parasitoids passively avoid elimination by developing in locations inaccessible to host hemocytes or by possessing surface features that fail to elicit an immune response. Other species actively disrupt the host immune system by injecting specific factors into the host at oviposition. In particular, polydnaviruses associated with several taxa of parasitoids disrupt capsule formation by killing hemocytes or altering their ability to adhere to foreign surfaces. These symbionts have likely played a critical role in evolution of host range and in defining parasitoid-host compatibility.

Butterflies are important flagship taxa for invertebrate conservation. Recent developments emphasizing species and habitat management based on sound ecological understanding exemplify progress in this emerging science. Studies in many countries show the complexity of management needs for single species, and examples of management and recovery plans demonstrate the worth of this approach. By contrast, in many tropical regions, where butterfly faunas are more diverse than in temperate zones and the resources for practical conservation are restricted, the major emphasis is on protection of habitats to safeguard relatively poorly documented assemblages, and on conservation measures that benefit local people. Aspects of butterfly ecology are discussed in relation to sound management of species and faunas, and selected examples from Europe, North America, and elsewhere exemplify increasing global interest in butterfly conservation.

At least 79% of predaceous land-dwelling arthropods use extra-oral digestion (EOD) as a means of utilizing relatively large prey with intractable cuticles. Through the injection of potent hydrolytic enzymes, either by refluxing or nonrefluxing application, these predators greatly increase the efficiency of prey extraction and nutrient concentration. The advantages of EOD are expressed ecologically as an abbreviation of handling time and an increase in the nutrient density of consumed food, allowing small predators to consume relatively large prey. The basis of EOD is a highly coordinated combination of biochemical, morphological, and behavioral adaptations that vary with different taxa.

The past decade has seen a resurgence of interest in developmental instability, reflected in fluctuating asymmetry, as a concept in evolutionary ecology. Many investigations interpret fluctuating asymmetry in populations or subsets of populations as reflecting the existence of, or at least the potential for, natural or sexual selection. However, the biological and nonbiological factors underlying the appearance of developmental instability are not well understood. For example, the ability of heterozygosity vs genomic coadaptation to have an impact on development and cause fluctuating asymmetry is still debated, though each will have important, but different, implications for the genetic structure of populations and genetic architecture of various traits. These and other issues reviewed in this chapter must be clarified in order for the concept of developmental instability to be meaningful in evolutionary and ecological studies.

Insect fat body historically has been considered a single tissue with multiple and diverse metabolic functions. Recent findings indicate that functionally distinct regions of fat body exist in some insects and that these regions often have unique morphologies. Regionally differentiated fat bodies in Lepidoptera have been associated with the segregation of synthetic and storage activities. The loss of biosynthetic capacity for storage proteins at the beginning of metamorphosis is the consequence of the histolysis of a larval specific histotype, whereas the histotype that accumulates storage proteins persists into the adult stage. In Diptera, functional histotypes are arranged along the anteriorposterior axis and between the larval and adult stages. Based on these models. we predict that the use of immunological and molecular probes will lead to the identification of regionally and functionally differentiated fat body histotypes in many insects.

Determination of the molecular modes of action of juvenile hormone to regulate gene expression has remained an elusive goal. This review discusses how studies on JH action have been influenced by the perspectives based on the mode of action of vertebrate retinoid/steroid hormones. Also identified are assumptions implicit in the experimental approaches used thus far, as well as alternative perspectives from which to frame future hypotheses on JH action.