PREDATION ON PUPAE OF HELICOVERPA-ARMIGERA HBN (LEP, NOCTUIDAE) AND ITS RELATION TO STEM BORER NUMBERS IN SUMMER GRAIN CROPS

Total predation on pupae of Helicoverpa armigera was correlated with t he numbers of larvae and pupae of the lepidopteran stem borers Busseol a fusca (Full.) and Chile partellus (Swin.) in maize and grain sorghum crops. The rate of predation on planted H. armigera pupae was the sam e as that on pupae that had pupated naturally. In summer, levels of pr edation were positively correlated with rainfall and negatively correl ated with maximum and mean temperature, but this was reversed in winte r. During the first period of the season (December-March) the ant, Dor ylus helvolus (L.), was the most important predator in three plots and the mouse, Mastomys natalensis (Smith), was dominant in three plots. During the rest of the year (April-November) D. helvolus was dominant in two plots and mice in three. Predation by D. helvolus on H. armiger a pupae was a numerical response with a higher percentage of pupae bei ng taken when stem borer numbers in the crops were higher. None of the other predators responded in their predation on H. armigera pupae to stem borer numbers. The correlation of predation by D. helvolus on H. armigera pupae with stem borer numbers suggests that the latter were a n important prey. Other predators in descending order of importance we re Cardiophorinae larvae, the Doryline ant Aenictus sp., larvae of Ast ylus atromaculatus B1. (Coleoptera, Melyridae), tenebrionid larvae, la rvae and adults of Heteronychus arator F., carabid larvae and adults, staphylinids and Dermaptera.