Effectiveness of entomopathogenic nematodes against sweet potato weevil (Cylas puncticollis) Boheman (Coleoptera: Apionidae) under semi-field conditions in Kenya

Abstract

Sweet potato (Ipomoea batatas (L.) Lam.) ranks second in production and value after cassava among the root crops in Kenya. Its production has been declining mainly due to the damaging effects of Cylas puncticolis Boheman (Coleoptera: Apionidae), its primary pest. Therefore, this study was done to determine effectiveness of two Entomopathogenic nematodes (EPNs) against C. puncticolis. The experiment was conducted under semi-field conditions using potted plants at Kibwezi, Eastern Kenya in two consecutive growing seasons in 2002 and 2003. Two species of EPNs were used and their efficacy compared: Steinernema karii Waturu, Reid and Hunt (Rhabditida: Steinernematidea) and Heterorhabditis indica Poinar, Karunakar and David (Rhabditida: Heterorhabitidea). Both EPNs significantly suppressed emergence of adult weevil from the tubers. The EPNs were also very effective on larvae and reduced the number of pupae significantly. The effect of the pest on the tuber quality was significantly high compared with its effect on tuber quantity. Among the EPNs, H. indica was more efficient in reducing the pest population and damage. In addition, the EPNs persisted in the soil for more than three 3 after their release. It is suggested that these EPNs have field potential in controlling the Cylas weevil and may provide the local solution to this pest problem in Kenya.