Chemosystematics And Evolution Of Beetle Chemical Defenses

Though mechanically well protected by an exoskeleton, Coleoptera, which comprise the largest group of organisms at the order level, have evolved a variety of defense mechanisms (21 , 39, 1 56). At each developmental stage beetles are protected by various structural modifications, types of behavior, mimetic, cryptic, or aposematic appearances, and, in particular, chemically based defenses (2 1 , 39). As a rule these defensive substances are multifunctional. As repellents, toxicants, insecticides, or antimicrobics they are directed against a large array of potential target organisms; they may also function as surfactants ( 10, 38). Although these allomones contribute to the fitness of the producers, it is often experimentally difficult or impossible to determine their adaptive value (9, 38). Usually Coleoptera biosynthesize and store their defensive compounds either in complex glands or in the hemolymph ( 10, 156) . In the latter case, toxicants are liberated by reflex bleeding; species that employ this defense often exhibit warning colorations or produce warning odors and may be models for mimicry (l0, 21) . Some beetles profit from exogenous plantand animal-derived toxicants, which are tolerated and sequestered (10). Since the last review on comparative aspects of beetle chemical defense in 1 978 ( 1 56), in which 330 species from 161 genera were considered, a wealth of information has emerged. To date, approximately 900 species from 380