Survey of parasitoids on lepidopterous stem borers attacking maize and sorghum in some localities of Ethiopia

Surveys were carried out for three consecutive years (1996/97-1998/99) to study the natural percent parasitism of indigenous parasitoids associated with stem borers attacking maize and sorghum in west, north and central Ethiopia. At all sites and localities, maize and/or sorghum fields were inspected for the presence of larvae and pupae of stem borers (Busseola fusca Fuller and Chilo partellus Swinhoe) and their parasitoids. The major parasitoids encountered were Apanteles sesamaie (Cameron)(= Cotesia):Bracon hebetor (Say); Bracon sesamiae (Cameron); Procerochasmis nigromaculatus (Cameron) (Ichntumonidae) and a Sarchophaga sp. (from order Dipter). An unidentified predaceous ant was also recorded. The surveys revealed the different percent parasitism depending upon the environmental conditions of the localities and availability of the hosts. This paper attempts to describe the natural percent parasitism and the potential of the above mentioned parasitoids in various locations of the country. The survey showed that Apanteles spp. is the dominant parasitoid group that attacks stem borers. Among the Apanteles parasitoid groups A. sesamiae (Cam) was found to be wide spread in all surveyed areas. Preliminary laboratory observations on A. sesamiae (Cam) also showed that is percent parasitism ranges from 20-60%. The number of adult parasitoids emerging from one host larva depends on the instar parasitized and varied with environmental conditions of the localities and availability of host. Roughly 60 and above adult parasitoides can emerge from a single parasitized larva. The most suitable larval stage for egg deposition was 4th to 6th instar. Both field and preliminary laboratory observations on percent parasitism suggest that A. sesamiae (Cam) is widespread and important for use in developing biological control program of maize and sorghum stem borers.