Diversity of stem borer parasitoids and their associated wild host plants in South Africa and Mozambique

The diversity of lepidopterous stem borers, their parasitoids and their associated wild host plants was studied in South Africa between 2006 and 2009 and in Mozambique between 2005 and 2010. In South Africa, 20 species of parasitoids were recovered from 17 stem borer species collected on 16 wild host plant species. From Mozambique, 14 parasitoid species were recorded from 16 stem borer species collected on 14 wild host plant species. The highest diversity of parasitoids was recorded on stem borers that attacked the host plants Phragmites australis (7 spp.) and Panicum maximum (6 spp.), in South Africa and Mozambique, respectively. Bracon sp. (Hymenoptera: Braconidae) and Procerochasmias nigromaculatus (Hymenoptera: Ichneumonidae) were the most recorded parasitoid species in South Africa while Cotesia sesamiae (Hymenoptera: Braconidae) parasitized most stem borer species in Mozambique. The most common tachinid parasitoid recorded in this study was Sturmiopsis parasitica (Diptera: Tachinidae). Parasitism of stem borers during the off season was previously thought to occur mainly in natural habitats but this study shows that although natural habitats provided refuges for some parasitoid species, stem borer parasitism was generally low in wild host plants, irrespective of whether collections were done during the cropping or off-season. Parasitoid beta diversity did not depend on habitat or host plant species, but was determined by stem borer diversity.