Regional distribution of lepidopteran stemborers and their parasitoids among wild grasses in the semi-arid eastern Kenya

Abstract

A survey was conducted in six agroecological zones (AEZs) in semi-arid eastern Kenya, in May, 1996, to identify the major wild host grasses (abundance > 70%) for stemborers in each zone. The grasses sampled were Pennisetum purpureum Schumach, P. trachyphyllum Pilg., Panicum maximum Jacq, Sorghum versicolor Anderss, Cenchrus ciliaris L. and Cyperus sp. Among these grasses, P. purpureumwas the most widespread and abundant. The survey was followed by an on-farm study conducted in each of the six AEZs to determine the relative abundance and distribution of stemborers, that infested the major wild grasses and heir parasitoids . This was done by destructive sampling of 100 tillers, at a three-month interval, from July 1997 to April 1998. The stemborers that infested the grasses were Chilo partellus Swinhoe and Sesamia calamistis Hampson. Among these, C. partelluswas the predominant species, with the highest number being recovered on S. versicolor (94.6%). Parasitoids were only reared on S. versicolor, and these were Cotesia sesamiae (Cameron), C. flavipes Cameron, Chelonus curvimaculatus (Cameron), Pristomerus sp. and Norbanus sp., with C. flavipes causing the highest parasitism (13.6%). Results reveal that S. versicolor exhibited potential for use in the management of stemborers in maize, by acting as a "trap" and "refuge" crop for C. flavipes, between cropping seasons.