Cotesia flavipes Cameron (Hymenoptera: Braconidae) was introduced in Uganda in 1998 for the biological control of the old association cereal stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). However there is little information on whether this parasitoid will attack new association Lepidoptera, which in turn may have implications on its efficacy on Ch. partellus. This study investigated the incidence of introduced Co. flavipes on Ch. partellus, and new association lepidopteran species and associated effects on its efficacy Parasitism levels for Co. flavipes in several locations varied between 13.7-34.8% and 1.5-18.8% on Ch. partellus and new association hosts, respectively. Implications for biological control of stemborers in Uganda are discussed. none