Biochemical Aspects of Insect Immunology

Abstract

Insects are among the oldest and the most successful groups of animals occupy­ ing this planet. An essential feature of the success of insects has been their ability to invade and to exploit a diverse range of ecological niches. Insects have evolved and, in many situations, thrived in environments replete with potential­ ly parasitic and pathogenic competitors. Disease in insect populations may reduce vigor, productivity, and ultimately survival of individuals and thus may contribute to the regulation of population levels. The ubiquitous presence of both infectious organisms and metazoan parasites in ecosystems occupied by insects has exerted a strong selection pressure for insects resistant to infection. Thus modem species of insects may represent the most extensive summary of successful defensive strategies against infection in the animal kingdom. In­ deed, several early studies of antimicrobial defense mechanisms in animals were performed using insect models (52). The defensive arsenal of insects, like that of man, contains both passive structural barriers against infection and a cascade of active responses to organ­ isms that gain access to the hemocoel following injury to the integument. These responses include both rapid changes in the circulating hemocyte population and the induced synthesis of new hemolymph proteins. In addition, active hemostatic mechanisms repair wounds in the integument and limit the extent of further infection. Much is known of the cellular and humoral defensive responses of insects to infective agents. However, this knowledge is often fragmentary and descriptive and is derived from a spectrum of species. Biochemical information on more than one aspect of insect defensive response for a single species is sufficient in