Some effects of weather and moonlight on light-trap catches of the army-worm, Spodoptera exempta (Walker) (Lepidoptera: Noctuidae), at Muguga, Kenya

Abstract

The effects of wind speed, wind direction, strong moonlight and rainfall on hourly light-trap catches of adult Spodoptera exempta (Wlk.) made at Muguga, Kenya, between January and June in 1970 and 1971 were investigated. The highest catches occurred in winds of 2–3 m/s, but generally, fewer moths were caught as wind speed increased. In totally dark hours the geometric mean catch at wind speeds of 5–6 m/s was about one-tenth that at 0–1 m/s. The relationship between catch and wind speed changed between January and June. Wind direction and change in direction were not significantly related to catch. The geometric means of catches made in strong moonlight were about one-tenth those in total darkness at comparable wind speeds. Rainfall was associated with higher catches in seven out of eight months, but the differences were significant in only two months. Recognition of the association between light winds and large numbers of S. exempta should assist forecasting, but a fuller understanding of the relationship between light-trap catch and population requires a method of population assessment that is independent of the effects of weather and moonlight.