The incidence and diapause of cereal stem borers, and the role of crop residues in the carry‐over of these pests on Rusinga Island in Kenya were investigated. The predominant stem borer infesting sorghum, the major cereal in this area, wasBusseola fusca.Another stem borer,Chilo partellusoccurred in very small numbers. However, a short‐rain sorghum or maize crop can be subjected to heavy infestation by both borers. The majority of the second generationB. fuscaon the long‐rain sorghum crop survived the off‐season (July/August‐February/March) as diapausing larvae in crop residues (stalks and stubbles).C. partelluson the other hand, survived mostly as an active population, but in low numbers. The number ofB. fuscain a 50 m2area of crop residues was reduced from 200 in September to 13 in February, the end of the off‐season. This small population mostly at the base of the stubbles appeared to be the source of infestation of the newly planted crop, and may have the potential of causing heavy infestation as each of the female moths emerging has an average fecundity of 650 eggs. Termination of diapause inB. fuscastarted in late November and reached a peak in February. Rainfall did not appear to be the main factor in the termination of diapause. On these observations it is clear that destruction of diapausingB. fuscaduring land preparation for the long rainy season crop, preferably by burning the stubbles, would be an effective cultural control method on Rusinga Island.