Spodoptera exempta (Wlk.) is predominantly a migrant species, but in southern Africa it is known that it can breed through several successive generations in one area. Similar observations were made for the first time in East Africa. Studies on populations in the Lambwe Valley in western Kenya revealed that during two years when the populations were monitored and one year when information was available from local farmers there were three generations each year during the period corresponding with the long rainy season. It is suggested that the Lambwe Valley presents a suitable habitat for the species to sustain its population and probably forms a breeding area for moths that might undergo large-scale migration.

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The effect of rain on insect survival is difficult to demonstrate with direct sampling techniques, specially in the adult stage. Observations were made in a sorghum field in Nairobi during the 1981 main rainy season, using yellow water pan traps, and data were examined using multiple regression analysis. Results indicate that rains, and more particularly heavy falls of rain occurring at the beginning of the rainy season, cause a substantial mortality among adults of the sorghum shootfly (Atherigona soccata Rondani). Rain does not adversely affect the survival of sorghum shootfly eggs, which are protected on the lower surface of leaves. Zusammenfassung Regen als Mortalitätsfaktor bei der Sorghum‐Fliege, Atherigona soccata Rond. (Dipt., Muscidae) Die Wirkung des Regens auf das Überleben von Insekten ist mit Sammelmethoden schwer zu belegen, besonders was die Adulten betrifft. Es wurden Untersuchungen in einem Sorghum‐Feld bei Nairobi während der Regenzeit 1981 unter Verwendung gelber Wasserschalen‐Fallen durchgeführt. Die Ergebnisse wurden der multiplen Regressionsanalyse unterzogen. Sie zeigen, daß Regenfälle, vor allem stärkere Niederschläge zu Beginn der Regenzeit, bei den adulten Sorghum‐Fliegen beträchtliche Sterblichkeit hervorrufen. Dagegen wirken sie sich für die geschützt an die Blattunterseiten abgelegten Eier nicht nachteilig aus.

The courtship behaviour of male Spodoptera exempta (Wlk.) has been quantified and used as a method of bioassay for the female sex pheromone. Virgin females become attractive to sexually mature males from 72 hr after emergence and henceforth their attractiveness increases gradually until they have mated. Mated females start losing their attractiveness to males gradually after mating and 72-96 hr after mating they cannot produce any courtship response in males. Amongst virgin females, crude pheromonegland extract and synthetic pheromone compounds, it is the older live females and the crude extract at 0.1 female equivalent that produce highest responses in males. A certain degree of cross-attraction between three coexisting species has been noted, both by using live insects as well as synthetic pheromone compounds of these species under laboratory bioassays. Possible interspecific pheromone-related implications are discussed.

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