Forecasting infestations of a migrant pest: the African armyworm Spodoptera exempta (Walk.)

A service for forecasting infestations of the larvae of Spodoptera exempta in Kenya, Tanzania and Uganda has been in operation since 1969; it uses nightly moth catches from a network of light traps, together with reports of larvae and meteorological information, to provide weekly forecast probabilities of larvae damaging cereal crops and grazing, in order that control measures may be organized in time. The principles on which the forecasting service is based, operational aspects, and the performance of the service to date, are summarized and illustrated by the formulation and subsequent verification of actual forecasts for representative periods of January and April for 7 years, as examples of the regular assessments undertaken to improve the accuracy of the forecasting service.