HOST PARASITOID INTERACTIONS - CRITICAL TIMING OF PARASITOID-DERIVED PRODUCTS/

Short-term in vitro incubations were used to examine the ability of en doparasitoid larvae to produce and release both ecdysteroids and prote ins into their environment. Second instar larvae of both Chelonus near curvimaculatus and Ascogaster quadridentata were observed by SDS-PAGE to release temporally-similar polypeptides in the 20-30 kD M-r range. Peak occurrence of these polypeptides coincided with shedding of the anal vesicle, immediately prior to ecdysis to the third instar. Ecdysi s also coincided with the switch from endoparasitic to ectoparasitic d evelopment in vivo. Polyclonal antibodies were generated against a par ticular 27 kD polypeptide of Chelonus, which was found to be species-s pecific and localized primarily within the anal vesicle during the lat ter part of the second stadium and whole body homogenates of third ins tars. In vitro incorporation studies using S-35-methionine indicated r apid changes in the synthetic abilities of second instar larvae shortl y before ecdysis. The production and release of ecdysteroids, as measu red by RIA, was found to precede the peak occurrence of the 27 kD poly peptide and ecdysteroid presence was undetectable following the molt. In contrast, the polypeptides were observed to gradually increase prio r to the molt and slowly decrease after the molt. The Chelonus polypep tide was not detected in host tissues until after parasitoid egression . (C) 1998 Elsevier Science Ltd. All rights reserved.