Can a specialist parasitoid, Macrocentrus cingulum (Hymenoptera: Braconidae), influence the ecotype structure of its preferred host Ostrinia nubilalis (Lepidoptera: Crambidae)?

Synchronization between a parasitoid and its preferred host is an essential strategy for successful biological control. Two ecotypes of Ostrinia nubilatis (Hubner) (Lepidoptera: Crambidae) in North America are distinguished by their voltinism. In this study, the differential impact of a specialist parasitoid, Macrocentrus cingulum Brischke (Hymenoptera: Braconidae), on the univoltine and multivoltine populations of 0. nubilatis is investigated. Four years of field and laboratory study suggested that M. cingulum emergence was synchronized with the spring emergence of the multivoltine ecotypes of O. nubilatis in Pennsylvania. Univoltine populations experienced minimal parasitism from M. cingulton. Field-collected data suggested that the postdiapause multivoltine O. nubitalis field population was male biased, whereas the univoltine population was female biased. M. cingulum-parasitized postdiapause 0. nubilatis larvae were significantly heavier than the male and noriparasitized female larvae. Sex ratio differences observed in overwintered 0. nubilatis populations in the presence or absence of M. cingulum parasitism suggested preferential parasitism between male and female 0. nubilatis larvae. Correlation between the larger parasitized 0. nubilalis larval host and the number of adult parasitoids emerging per host suggested a potential evolutionary advantage to parasitizing female or larger hosts.