Progeny production and sex ratios of the parasitoids Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) and its exotic congener Cotesia flavipes Cameron (Hymenoptera: Braconidae) emerging from three species of field-collected stemborers were compared. There were no significant differences in numbers of progeny of the two parasitoids from the African stemborers, Chilo orichalcociliellus (Strand) (Lepidoptera: Pyralidae) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae). Cotesia flavipes produced more progeny than C. sesamiae on large larvae of its coevolved Asian host, Chilo partellus (Swinhoe). No significant differences in the number of parasitoid progeny were observed for different-sized Ch. orichalcociliellus or S. calamistis larvae. These data suggest that under field conditions, Co. flavipes may be superior to Co. sesamiae as a parasitoid of its co-evolved host, Ch. partellus.
