Seasonal Incidence of Fall Armyworm on Maize and Its Relationship With Weather Parameters

Abstract

Fall armyworm, Spodoptera frugiperda, has become one of the most closely watched pests of maize in Africa and Asia, and a large body of local work reports how its numbers rise and fall through the cropping year in relation to temperature, rainfall and humidity. This narrative review asks what that literature can and cannot tell a grower or adviser who wants to anticipate the pest. It draws on published work on the biology, migration and natural enemies of the insect, on how weather shapes its development and flight, and on the methods used to monitor it, and it reports no new data. The reviewed studies agree on a broad picture: warm conditions speed development, rainfall and humidity act in mixed and local ways, and incidence tends to follow the crop stage and the arrival of moths. The correlations between weather and pest counts, however, are site-specific and often change sign between seasons. Trap types and scouting rules differ, so counts are not directly comparable, and planting date, crop stage and natural enemies are tangled with weather in most field series. The review concludes that weather is best treated as one modifier of a seasonal pattern that is driven by crop phenology and immigration, and it sets out the design and reporting features that would let future seasonal studies be compared and combined.