Seasonal occurrence, parasitoids and pathogens of the African stem borer, Busseola fusca (Fuller) (Lepidoptera : Noctuidae), on cereal crops in South Africa

This study was carried out in maize and grain sorghum fields near Delmas in the Highveld Region of Mpumalanga Province, South Africa, from 1986/87 to 1992/93. Infestation of maize and sorghum by larvae and pupae of Busseola fusca (Fuller) peaked from February to April, then declined rapidly when the crops matured during May. Larvae that infested the crops during January and February diapaused in winter as mature larvae, pupated by October and moths emerged during October and November. Larval parasitoids were active from February to May, with parasitism peaking at 40 % at the end of the growing season in May. Peaks of larval parasitism lagged about four weeks behind peaks of larval populations and were manifested when populations were declining. The most abundant larval parasitoid of B. fusca was Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae), which was active throughout the growing season and in spring. Pupal parasitoids were abundant only during the 1989/90 growing season, peaking at around 50 % parasitism during October. The most abundant pathogen of B. fusca was the nucleopolyhedrosis virus (NPV), which occurred throughout the growing season and in winter, and caused mortality during March to May that coincided with peak larval populations. Larval parasitoids, especially C. sesamiae, and microbial pathogens, especially NPV, were the major cause of the autumn decline in the larval populations of B. fusca. Timing of male moth flights of B. fusca, determined by the use of synthetic sex pheromone traps, was consistent, with three peaks each year. The first flight, which resulted from moths emerging from pupae that emanated from larvae that hibernated in spring, peaked around the middle of November, while the second and the third flights peaked around the middle of February and April, respectively.