Seasonal fluctuations of noctuid stemborer egg parasitism in southern Benin with special reference to Sesamia calamistis Hampson (Lepidoptera : Noctuidae) and Telenomus spp. (Hymenoptera : Scelionidae) on maize

Parasitism of noctuid stemborer eggs was assessed in monthly surveys in mai ze Welds in southern Benin, from May 1995 to October 1996, and on alternati ve hosts, i.e. wild grasses, during the dry season from November 1995 to Fe bruary 1996. Sesamia calamistis was the most prevalent stemborer species, a ccounting for 98% of the larvae identified from subsamples reared on ear pi eces. Egg batch densities ranged between 0.02-0.15 per plant, with lowest d ensities found during high rainfall periods. 77% of all egg batches were fo und to be parasitized The egg parasitoids were the scelionids Telenomus bus seolae, T. isis, and the trichogrammatid Lathromeris ovicida, accounting fo r 55.6, 41.6 and 2.8% of total counts, respectively. Parasitism increased i n the course of the cropping season and reached peaks of 92 and 86% during the second growing season of 1995 and 1996, respectively. This coincides wi th the time when farmers have planted a second crop and during a stage when the plants were most attractive and susceptible to S. calamistis attacks. During the dry season, relatively high parasitism was found on maize and wi ld grasses in inland valleys, and it was concluded that those habitats play an important role in stabilizing the system for both the pest and its natu ral enemies. As a result, in the Dahomey Gap, which includes parts of Benin , Togo and Ghana, S. calamistis is usually not of economic importance. Alth ough T. busseolae is ubiquitous in Africa, T. isis was only reported from W est Africa, including Cameroon. It is recommended that the geographic range of T. isis should be expanded and include East and Southern Africa, where another host, Busseola fusca, is the most important noctuid stemborer pest on cereals.