The stem borers, Busseola fusca (Fuller) (Lepidoptera: Noctuidae)
and Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), are the most
important pests of maize and grain sorghum in South Africa. Parasitoids,
pathogens and predators curtailed populations of B. fusca and C.
partellus on the crops but their activity was not enough to reduce pest
populations to below economic damage level. They also could not prevent the
dispersal and subsequent wide distribution of C. partellus after its
introduction into South Africa.
Nine indigenous parasitoids and hyperparasitoids have been recorded attacking
both borer species. These parasitoids are probably more habitat specific with
regard to foraging for hosts than they are host-specific as they appear to have
moved from their indigenous hosts to use C. partellus as a new
alternative host. Between 1977 and 1993 three braconids, one eulophid, three
ichneumonids, two trichogrammatids and four tachinids were introduced into South
Africa from 11 countries for biological control of stem borers. Recoveries of
parasitoids were made only short periods after releases and in the vicinity of
the release sites. However, cold and dry winters, with night temperatures often
falling to below freezing prevail in the Highveld Region, which is the major
summer grain producing areas of South Africa. These conditions, and the fact
that borers enter diapause in the dry stalks for a period of 7 months in winter,
when the crops or other alternative host plants such as grasses do not grow,
hamper the establishment of exotic natural enemies in the Highveld Region.
Chilo partellus and its natural enemies are reared for research
purposes. Exotic parasitoids of stem borers were introduced and, after
quarantine, were studied in the laboratory and released in the field for
biological control to augment the local assemblage of natural enemies.
Kfir, R. 1997.
Natural control of the cereal stem borers Busseola Fusca &
Chilo Partellus in South Africa. Insect Science and its
Application 17: 61-68.