Intrinsic competition between two oligophagous parasitoids, Sturmiopsis parasitica and Cotesia sesamiae, attacking the same life stages of lepidopteran cereal stemborers

Host acceptability and suitability of four cereal stemborers (Lepidoptera) commonly occurring in eastern Africa, Sesamia calamistis Hampson, Busseola fusca (Fuller) (both Noctuidae), Chilo partellus Swinhoe (Crambidae), and Eldana saccharina Walker (Pyralidae), for a West African strain of Sturmiopsis parasitica (Curran) (Diptera: Tachinidae) were assessed. In addition, the outcome of multi-parasitism was studied using a local strain of the endoparasitic Cotesia sesamiae Cameron (Hymenoptera: Braconidae) as the competing parasitoid. Various parasitism sequences and time intervals between parasitism were chosen. Parasitism increased linearly with the number of planidia used per larvae and was 80% with eight planidia. All species were accepted for larviposition, but suitability varied greatly; parasitism was 75.2, 37.9, 34.8, and 23.8% with S. calamistis, B. fusca, E. saccharina, and Ch. partellus, respectively. Sturmiopsis parasitica outcompeted Co. sesamiae irrespective of the time interval between parasitism, and whether it was the first or second species to parasitize. This was mainly due to a longer egg-to-cocoon development time and a high cocoon-to-adult mortality in Co. sesamiae. The implications of these results for expanding the geographic range of the West African strain of the tachinid in Africa are discussed.