Flight and oviposition behaviour of the African stem borer, Busseola fusca, on various host plant species

The African stem borer, Busseola fusca (Fuller) (Lepidoptera: Noctuidae), is an important pest of maize and sorghum in sub-Saharan Africa. As in many other lepidopteran insects, the ability of B. fusca to recognize and colonize a variety of plants is based on the interaction between its sensory systems and the physical and chemical characteristics of its immediate environment. In this study, we tried to identify the behavioural steps of B. fusca leading to host selection and oviposition. Three Poaceae species commonly cultivated in Kenya for human consumption and animal forage were used in this study: the two most preferred hosts, maize (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench], and one non-preferred host, Napier grass (Pennisetum purpureum Schumach). Wind tunnel observations revealed that volatiles produced by the different plant species did not appear to strongly influence the general orientation of B. fusca towards the plant, as similar behavioural steps were exhibited by the female moth regardless of the plant species involved. This indicated that the females were not able to recognize their preferred hosts from a distance. After landing, the female typically swept her ovipositor on the plant surface, simultaneously touching it with the tips of her antennae, and then oviposited. This behaviour was more frequently observed on maize and sorghum than on Napier grass, and indicated that both antennal and ovipositor receptors are used by the female moths to evaluate the plant surface before deciding to oviposit. As a result, the females laid more eggs on the two crops than on Napier grass. We conclude therefore that females recognized their preferred hosts only after landing. Tactile and contact-chemoreception stimuli from the plants seemed to play a major role in oviposition decisions of B. fusca.