Published online by Cambridge University Press: 10 July 2009
Records of daily catches of males of Spodoptera littoralis (Boisd.) at pheromone traps in or near the Nile Delta, Egypt, during 1979 and 1980 were used to investigate both the seasonal variation in catch and the possibility that migration, associated with particular weather systems, may significantly affect moth numbers in a particular area. Although more moths were caught in 1979 than in 1980, in both years there was a similar seasonal variation in catch, with low numbers in January and February followed by an increase to a maximum in June or August. There was no systematic seasonal change in the area of highest catch that would suggest seasonal migrations. On some nights, large increases in catch were associated with weather disturbances, notably windshift lines, suggesting that flying moths are sometimes redistributed by wind systems. Catches at two traps far from the main source area suggest that moths may have flown at least 50 km downwind from sources in the Nile Delta. The pattern of nightly catches at most traps indicated that build-up of local populations is the most important factor affecting the population dynamics of the pest but that some, mainly local, redistribution by wind systems takes place.