The microbial insecticide,Bacillus thuringiensisBerliner var.kurstaki(Dipel 10G), was effective against larvae of the maize stalk borer,Busseola fusca(Fuller), in two separate trials in Kitale, Kenya during the 1987 growing season. In the first trial,B. thuringiensisapplied at different times, was compared against DDT (5% dust), endosulfan (Thiodan 3G), trichlorphon (Dipterex 2.5G), ash, diatomaceous earth, and an untreated control. The level of suppression provided by the laterB. thuringiensistreatments was equivalent to DDT and trichlorphon but inferior to endosulfan. Ash and diatomaceous earth treatments proved ineffective. In the second trial, destructive sampling ofB. thuringiensis‐treatedplots and untreated control plots was used to assessB. thuringiensis'sImpact on the nature and degree of stalk borer infestation. Four developmental categories were assigned to larvae of various head capsule widths and pupae comprised a fifth category. Significantly(P <0.05) fewer individuals of all but the first developmental category were found in the plants treated withB. thuringiensis.Results suggest thatB. thuringiensismay have residual activity againstB. fuscalarvae for at least 3½ weeks after application when applied directly in whorls.