PARASITISM-INDUCED EFFECTS ON HOST GROWTH AND METABOLIC EFFICIENCY INTOBACCO HORNWORM LARVAE PARASITIZED BY COTESIA-CONGREGATA

Parasitism by the braconid wasp Cotesia congregata affects the growth of Manduca sexta larvae in a parasitoid 'dose-dependent'' fashion. Fol lowing parasitization of fourth-instar larvae, more heavily parasitize d larvae grew larger compared to those containing fewer parasitoids du e to an increase in host dry weight. The differences in host mass appe ared to arise after oviposition. A 'dose-dependent' enhancement of hos t dry weight would appear nutritionally beneficial for the parasitoids developing in more 'crowded' hosts. The efficiencies of conversion of ingested and digested food to body mass and the approximate digestibi lity of the diet ingested by the host caterpillar did not vary signifi cantly with clutch size although parasitoids took slightly longer to d evelop in the more heavily parasitized hosts. Larval parasitoids devel oping in the presence of many competitors weighed up to 50% less than those developing in hosts with fewer endoparasitoids, although the wei ght of adult female parasitoids did not vary significantly with wasp c lutch size. The maximum number of emerging wasps wits 200 parasitoids, possibly representing the host's 'carrying capacity' for larvae paras itized in the fourth-instar, The ratio of emerging to non-emerging par asitoids decreased as parasitoid clutch size increased, with few or no ne emerging from very heavily parasitized hosts containing more than 4 00 parasitoids. (C) 1997 Elsevier Science Ltd.