PARASITOID ENCAPSULATION AS A DEFENSE-MECHANISM IN THE COCCOIDEA (HOMOPTERA) AND ITS IMPORTANCE IN BIOLOGICAL-CONTROL

Encapsulation is a common defense mechanism exerted by a host insect i n response to invasion by a metazoan parasitoid or other foreign organ isms. In the process of encapsulation, the host forms a capsule around the parasitoid egg or larva, which is usually composed of host blood cells and the pigment melanin. The capsule may kill the parasitoid and thus prevent successful parasitism. Encapsulation may adversely affec t the degree of biological control effected by parasitoids as it may e ither prevent the establishment of exotic parasitoids in new regions o r reduce parasitoid efficacy. A high incidence of encapsulation may al so cause difficulties in mass rearing of parasitoids, In the Coccoidea (Homoptera), parasitoid encapsulation has so far been recorded in thr ee families: Coccidae (soft scale insects), Diaspididae (armored scale insects), and Pseudococcidae (mealybugs), Important factors that affe ct the frequency of parasitoid encapsulation in the Coccoidea include: Host and parasitoid species, the host's physiological age and physiol ogical condition, the host origin (or strain), superparasitism, the re aring and/or ambient temperature, and the host plant, The effects of t hese factors on the incidence of parasitoid encapsulation in the Cocci dae, Diaspididae, and Pseudococcidae are described. (C) 1997 Academic Press.