Diversity of stem borer egg parasitoids and patterns of parasitism in Morogoro and coast regions in Tanzania

Studies to determine the diversity of stem borer egg parasitoids and patterns of parasitism were carried out in Morogoro and Coast regions in Tanzania from January to December 2006. During the cropping season, sampling was done on maize/sorghum fields and during the off-season, the survey continued by sampling from alternative wild host plants. Farmers’ fields were randomly chosen approximately 5 – 8 km intervals from each other and approximately 15 – 20 metres from the roadside. Plots measuring approximately 40 m x 40 m were demarcated and sampled at each study site. Each field was divided into four quadrats and an equal number of plants (20 from each quadrat) were randomly chosen and thoroughly checked for stem borer eggs. Sampling began 14 DAP and continued once every month. The eggs were incubated at ambient laboratory temperature and humidity (approximately 27 } 1 0C and 70 } 5% R.H) for two weeks after which all larvae or parasitoids had emerged. Egg batch parasitism was determined by taking the ratio of parasitized to unparasitized egg batches and parasitism within a parasitized egg batch was determined by taking the ratio of parasitized to unparasitized eggs. The egg parasitoids species recovered were Trichogramma nr. mwanzai, Trichogrammatoidea nr. armigera, Trichogrammatoidea nr. lutea, Trichogramma spp., Telenomus nemesis, Telenomus spp and Trichogrammatoidea species. The stem borer species were determined in the field based on the arrangement of eggs on the leaf/stem surface. C. partellus was found to be the most prevalent stem borer species, accounting for 85.65%, S. calamistis accounted for 11.54% and other unidentified species accounted for 2.81% of all egg batches. B. fusca and C. orichalcocillielus were of minor importance in this study. It is concluded that Coast region has significantly higher levels of parasitism of stem borer eggs and a wider range of parasitoid species when compared to Morogoro.