1. Comparison of dominant wind directions with seasonal redistribution of Spodopteru exempta caterpillar outbreaks in East Africa provides further circumstantial evidence to support the hypothesis of downwind migration by adult moths. 2. Calculated backward and forward tracks for sixty-nine nights during the 1973-74 and 1974-75 seasons, when there were sudden increases in numbers of moths caught at six light traps, illustrate the variability of downwind movement due to the effects of temporary atmospheric disturbances.3. Comparison of calculated tracks with known outbreaks before and after the nights of increased moth catch suggests that some outbreaks are derived from unreported sources, especially eariy in the season, and it.is therefore unwise to link new outbreaks only with known earlier ones.