The relationship between outbreaks, rainfall and low density populations of the African armyworm, Spodoptera exempta, in Kenya

This study has demonstrated that low numbers of African armyworms (Spodoptera exempta) (Walker) (Lepidoptera: Noctuidae) can be found throughout the year in parts of the coastal and highland regions of Kenya where there is frequent rainfall. During the study period the numbers of moths caught in pheromone traps in these regions built up during the short and long rains, and decreased dramatically during the intervening dry seasons. There was a lag of one to two months between the peaks for rainfall and moth numbers. This contrasts with the situation at sites of the seasonal outbreaks of armyworm larvae, where a sudden preceding influx of moths coincides with the rainfall. A positive correlation was found, for the long rains seasons only, between the number of armyworm outbreaks throughout the country and the peak numbers of moths in coastal and highland regions.

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