Parasitoids of the Asian corn borer, Ostrinia furnacalis (Guenee), and their biological attributes

Three larval-pupal parasitoids of the Asian corn borer (Ostrinia fumacalis (G.) were collected: Xanthopimpla stemmator (Wlk.) Ichneumonidae, Brachymeria obscurata (Thunb.) Chalcididae, and Trichomma cnaphalocrosis Uchida, Ichneumonidae. Among the three, T. cnaphalocrosis overwhelmingly satisfied the biological attributes of a potential biological control agent. It was the most abundant and most capable of parasitizing the corn borers under field conditions. It parasitized the corn borers over the longest period of 40 d starting from the blister stage to physiological maturity of the corn plants. The parasitoid B. obscurrata also had a parasitization period of 40 d, but the rate was consistently low. The most promising biological control agent that can be reared for release in the field is T. cnaphalocrosis. T. cnaphalocrosis emerged from the pupae of corn borers 1 to 5 d later than the expected emergence of adult borers in healthy pupae. Only the late instar larvae (the V 4th and 5th instars) harbored the parasitoids that emerged during the pupal stage. T. cnaphalocrosis parasitized its host while the larvae were still feeding on accumulated pollen at the corn tassels, leaf buds, leaf sheats, leaf axils and silk, and before the late third or fourth instar migrated to the corn stalks. The third instar larva was preferred for oviposition. Adult emergence usually occurred from 6:00 to 9:00 a.m. The adults fed on solutions of sugar and honey mixed with pollen. Courtship and mating started immediately after emergence, lasting from 4 to 5 h between 8:00 a.m. and 5:00 p.m. Mating continued even when the pairs were in flight. Adult longevity of males and females was 4 d.