Intercropping and weeding: effects on some natural enemies of African bollworm,Heliothis armigera(Hbn.) (Lep., Noctuidae), in bean fields

The effects of strip-cropping haricot bean (Phaseolus vulgaris L.) with maize (Zea mays L.) under weedy and weed-free conditions on the abundance of tachinid parasitoids and a predatory wasp (Tiphia sp. ?sjostedti Cameron) that are associated with African bollworm [Heliothis armigera (Hbn.)] were studied at Awassa, southern Ethiopia, during the 1987 and 1988 crop seasons. Tachinids were more abundant in strip-cropped and weedy plots than in bean monoculture. Strip-cropping had no effect on Tiphia numbers whereas the wasp was 2- to 8-times more abundant in weedy than in weed-free plots. In general, tachinid and Tiphia numbers increased with increasing habitat diversity.