Establishment of an exotic parasitoid Cotesia vestalis, (Hymenoptera: Braconidae) in selected study sites as a biological control agent of Diamondback Moth, Plutella xylostella L. (Lepidoptera: Plutellidae) in Kenya

Abstract

The diamondback moth Plutella xylostella (L) is a serious pest of cruciferous crops in most parts of the world. Use of chemical pesticides has been the main method adopted by farmers in a bid to control this pest. However, with the indiscriminate pesticide use, this pest has developed resistance to several insecticides. Moreover, insecticides are hazardous to the environment, consumers, sprayers as well as beneficial insects. Biological control using natural enemies has been suggested as an important component in the integrated management of the P. xylostella. In an effort to control the pest and minimize insecticide misuse, ICIPE was involved in a classical biological control project that involved importation and release of Cotesia vestalis from South Africa into the lowlands of Kenya in 2004. However, a survey carried out two years later indicated that the parasitoid had not established since only few parasitoids were recovered from the sites of release. Additional releases were done in Kwale, Kajiado, Kitui, Machakos and Makueni counties. The objectives of this study were to follow-up on the establishment and parasitism rates of the released C. vestalis, to characterize the samples through molecular techniques and identify factors affecting its establishment. Surveys were carried out in five Counties of Kenya: Kajiado, Kitui, Makueni, Machakos and Kwale County where sampling of ten randomly selected cabbages or kales per farm and collection of parasitoid pupa and the P. xylostella larvae and pupa. The numbers of P. xylostella and the parasitoids that emerged from the collected samples were recorded and the data was used to calculate the parasitism rate by C. vestalis. A well-structured questionnaire was used to collect information on cultural practices and farmers knowledge on use of natural enemies in pest management. The study showed that C. vestalis had established in its release sites but its parasitism rates remain very low, molecular techniques confirmed that the samples were Cotesia vestalis and cultural practices affecting establishment were irrigation, intercropping and use of pesticides. Therefore, farmers need to reduce the use of chemical insecticides and adopt more use of Bt products, increase farmers knowledge on biological control and adopt use of trap crops.