Naive females of Cotesia flavipes Cameron and Cotesia sesamiae (Cameron) were attracted, in a T-tube olfactometer, to volatile kairomones from frass produced by Chilo partellus (Swinhoe), Chilo orichalcociliellus Strand, Sesamia calamistis Hampson, and Busseola fusca (Fuller) fed on maize (Zea mays L.), sorghum (Sorghum bicolor (L.)), and napier grass (Pennisetum purpureum Schumach). In dual-choice tests, C. flavipes and C. sesamiae were generally unable to discriminate between volatiles from frass produced by any of the four different stemborer species fed on maize stalk. When larvae of C. partellus and S. calamistis were washed in distilled water, their acceptance by both parasitoid species was reduced.