Survey and experiments were conducted to investigate the distribution and bionomics of the rice stem-borers in Kenya. Stem-borers collected and identified included: Maliarpha separatella Rag., Diopsis thoracica West, Sesamia calamistis Hmps. and Chilo partellus Swin. Maliarpha separatella were most abundant and infested throughout the crop season, D. thoracica infested during vegetative phase. S. calamistis frequently occurred at the onset of flowering stage toward harvest. C. partellus occurred more frequently in upland than lowland rice and was at low population. Assessment of crop loss caused by M. separatella was carried out under field, caged condition. It was observed that the per cent of empty grains was affected by Maliarpha infestation. Calculated yield loss based on percentage empty grains and number of ‘whiteheads’ was higher than the actual differences between grain weight of uninvested and infested crops.
