A Survey of Fungal Pathogens of Aphids from South Africa, with Special Reference to Cereal Aphids

Parasitoids are often members of species complexes and are difficult to identify by conventional morphology, although most indigenous parasitoids of muscoid flies can be identified from adults. Pupal exuviae of the gregarious parasitoids Muscidifurax raptorellus Kogan and Legner and Nasonia vitripennis (Walker) were dissected from parasitized house fly (Musca domestica L.) puparia. Their hydrocarbons were extracted, isolated, and analyzed via column and gas chromatography, as were those of adult parasitoids. Quantification of 7-methylhentriacontane and 3,7,15-trimethylpentatriacontane allowed calculation of peak ratios of these two methyl-branched components that showed statistically significant differences between the species. Since the profiles were dramatically different, a confident identification resulted. Analysis of adult parasitoids or the mummified host remains from parasitized host puparia also revealed distinctive hydrocarbon profiles between species, and the same peak ratios were definitive for each species. Since there are no morphological keys for pupal life stages, hydrocarbon profiles provide a simple and reliable method to identify parasitoids from parasitized host puparia, before or after the adult parasitoids have left the host. In addition, the parasitoid species found in parasitized pupae can be determined from analysis of the empty puparium or even the mummy itself.