The effects of 3 trophic levels of insect pests on various intercropping systems of maize, cowpea [Vigna unguiculata] and sorghum were investigated in Kenya in 1981-82. The trophic levels were specialist feeders subsisting only on 1 crop within the intercropping systems (such as Maruca testulalis (Geyer) on cowpea and Atherigona soccata Rond. on sorghum), relatively specialist feeders on 2 of the 3 crops (such as Busseola fusca (Fuller), Chilo partellus (Swinh.), Sesamia calamistis Hmps. and Eldana saccharina Wlk. on maize and sorghum) and generalist feeders (such as Heliothis armigera (Hb.) on all 3 crops). On the basis of yields per unit area of crop, the best cropping patterns were maize with cowpea and sorghum at a land equivalent ratio (LER) of 1.45, and sorghum with cowpea at 1.3 LER. High losses in combinations of maize with sorghum at 0.89 LER suggested that stem-borer colonisation at an early stage of crop establishment, resulting in dead-hearts and reductions in plant populations per unit area, contributed to the overall reduction in crop turnover wthin such mixtures