Parasitism-induced effects on host growth and metabolic efficiency in tobacco 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. Following parasitization of fourth-instar larvae, more heavily parasitized larvae grew larger compared to those containing fewer parasitoids due to an increase in host dry weight. The differences in host mass appeared to arise after oviposition. A 'dose-dependent' enhancement of host 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 digestibility of the diet ingested by the host caterpillar did not vary significantly with clutch size although parasitoids took slightly longer to develop in the more heavily parasitized hosts. Larval parasitoids developing in the presence of many competitors weighed up to 50% less than those developing in hosts with fewer endoparasitoids, although the weight of adult female parasitoids did not vary significantly with wasp clutch size. The maximum number of emerging wasps wits 200 parasitoids, possibly representing the host's 'carrying capacity' for larvae parasitized in the fourth-instar, The ratio of emerging to non-emerging parasitoids decreased as parasitoid clutch size increased, with few or none emerging from very heavily parasitized hosts containing more than 400 parasitoids. (C) 1997 Elsevier Science Ltd.