Distribution and Relative Importance of Lepidopteran Cereal Stemborers and their Parasitoids in Uganda

Abstract

Infestation levels and parasitism of lepidopteran stemborers on maize were assessed in four agroecological zones (AEZ) in Uganda. The indigenous noctuid Busseola fusca Fuller (Noctuidae) and the invasive Chilo partellus Swinhoe (Crambidae) were the most important stemborers recorded. C. partellus represented 77% of the stemborers in the Eastern AEZ while B. fusca was dominant in the other AEZs, accounting for 60-79%. The proportion of infested plants was between 16% and 45% and borer density between 0.2 and 1.0 borers per plant. There was no clear relationship between damage and stem tunneling, which is often used to estimate yield loss. Telenomus busseolae Gahan (Scelionidae), the only egg parasitoid recovered, caused parasitism of up to 46% on B. fusca eggs. Several larval and pupal parasitoid species were recorded. The most common were the indigenous braconid Cotesia sesamiae and the introduced Cotesia flavipes, which are larval parasitoids of B. fusca and C. partellus, respectively. Mean parasitism by the indigenous C. sesamiae ranged between 2.0% and 29.4% on B. fusca and from 0 to13% on C. partellus. C. flavipes was recovered at most locations with parasitism of 0-30.5% on C. partellus and 0-12% on B. fusca; the latter was probably the result of multiparasitism as laboratory studies have shown that it was not a suitable host for C. partellus. Results indicated further that the parasitoid has not attained equilibrium 5 years after its introduction.