INSTAR-DEPENDENT HEMOCYTE CHANGES IN PIERIS-BRASSICAE AFTER PARASITIZATION BY COTESIA-GLOMERATA

Cotesia glomerata L. (Hymenoptera: Braconidae) is a parasitoid of earl y instar larvae of Pieris brassicae L. (Lepidoptera: Pieridae). Late i nstars of P. brassicae can more often overcome parasitization by hemoc ytic encapsulation of C. glomerata eggs. Short-term hemocyte responses to parasitization were examined in third and fourth instar larvae of P, brassicae. Total and differential hemocyte counts did not differ be tween parasitized and unparasitized host larvae. A rapid, but temporar y decrease of total hemocyte as well as plasmatocyte numbers was obser ved immediately after oviposition. Numbers of hemocytes adhering to ti ssues were shown to be the same in untreated, wounded and parasitized P. brassicae larvae by tracing hemocytes with monoclonal antibodies as markers. The in vitro spreading ability of hemocytes from unparasitiz ed third and fourth instar larvae was lower than that of the last inst ar's; parasitization, however, had no influence on hemocyte spreading. We therefore suggest that the higher parasitization success of C. glo merata in earlier instars of P. brassicae is mainly due to the low spr eading ability of the hemocytes.