none Developmental time of the polyembryonic parasitoid Macrocentrus grandii in larvae of Ostrinia nubilalis , the European corn borer was shown to be shortest under a warm-temperature regime and in laterhost instars. Temperature had a significant effect upon parasitoid development during both host-internal and host-external phases, whereas host instar proved important only during the former developmental phase. The number of parasitoids emerging from each host showed a dramatic increase from 20 to 25 degree C. The ability of emerged parasitoids to reach the pupation stage successfully also was affected significantly by temperature, with an optimum of 25 degree C. A peculiar phenomenon involving abnormal pupal development in the European corn borer observed during the study suggests that alteration of the normal host-parasitoid relationship occurred at cooler temperatures (15-20 degree C). Life cycle and development; Development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Abiotic factors; Physical factors Ostrinia nubilalis (Pyralidae); Hymenopteran parasites; Macrocentrotus grandii; Parasite development time, effect of host instar; Host parasite relationships; Host instar, effects on hymenopteran parasite postembryonic development Macrocentrus grandii (Braconidae); Postembryonic development; Developmental time, temperature & lepidopteran host instar relationships; Lepidopteran hosts; Ostrinia nubilalis; Parasite development time, effect of host instar; Host parasite relationships; Lepidopteran host instar, effects on postembryonic developmental time; Temperature; Postembryonic developmental time in lepidopteran host, effects