Interspecific competition between Xanthopimpla stemmator Thunberg and Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae), pupal parasitoids attacking Chilo partellus (Lepidoptera: Crambidae) in East Africa

Interspecific competition between Xanthopimpla stemmator and Dentichasmias busseolae was studied using pupae of the invasive crambid stemborer Chilo partellus as the host. While X. stemmator is an old association, D. busseolae formed a relatively new association with C. partellus in East Africa. Two different time intervals between parasitism (0 and 48 h) and two parasitoid sequences i.e., X. stemmator before D. busseolae (Xs–Db) and D. busseolae before X. stemmator (Db–Xs)] were chosen. In addition, the parasitoids’ performance on pupae in maize stems and ears was assessed. For both X. stemmator and D. busseolae, there was no difference in foraging time between unparasitized pupae and pupae previously parasitized by the other species, indicating that the two species were not capable of interspecific host discrimination. In the Xs–Db sequence, the time interval between parasitism did not have an influence on the percentage of pupae producing either parasitoid species. By contrast, in the Db–Xs sequence, the percentage of pupae producing X. stemmator was almost 8 times higher in the 0-h than the 48-h interval, while for D. busseolae it was the reverse. In the 0-h interval, X. stemmator outcompeted D. busseolae irrespective of whether it parasitized first or second, while in the 48-h interval, the parasitoid parasitizing first won. While D. busseolae successfully searched for and parasitized pupae in both stems and ears, parasitism of pupae in ears by X. stemmator was negligible. It was concluded that the two species could co-exist because they partly exploit different ecological niches.