Performance of cotesia flavipes cameron (hymenoptera: braconidae) on stem borers of cereals and wild crops.

Abstract

The braconid larval parasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae) was introduced into Kenya from Pakistan and India for the control of the exotic crambid stem borer Chilo partellus Swinhoe (Lepidoptera: Crambidae). In Africa, maize fields are usually islands surrounded by land occupied by wild gramineous plants. Many of the wild plants harbour borer species not found on crops. It is not known if the exotic parasitoid C. flavipes follows these borers into the wild habitat and whether they are suitable for its development. Thus, the purpose of this study was: i. to assess the suitability of some borer species found in crops and wild host plants for the development of C. flavipes, ii.to study the host-foraging behaviour of the parasitoid and iii. to isolate and identify plant volatiles that could mediate host finding by C. flavipes. Seven stem borer species were used: C. partellus and Busseola fusca Fuller (control species), Sesamia calamistis Hampson, two populations of S. nonagrioides Tams & Bowden (from Eastern and Western Kenya), B. phaia Bowden and Sciomesa piscator Tams. C. partellus, S. calamistis and B. fusca are mostly found on cultivated crops whereas S. nonagrioides (especially eastern population), B. phaia and S. piscator are mostly found on wild host plants. The stem borer species exposed to C. flavipes were equally acceptable for oviposition. However, the suitability varied with species. Parasitoid emergence occurred only on C. partellus, S. calamistis and the S. nonagrioides West population, while species feeding on wild hosts plants were not suitable. C. flavipes females were significantly more attracted to volatiles from stem borer-infested plants than to volatiles from uninfested plants regardless of stem borer and the plant species used. This was probably due to the richer chemical profile of stem borer-infested plants and especially in green leaf volatiles and terpenoids compared to uninfested plants. It can be concluded that the unsuitable borer species used in the present experiment form a reproductive sink.