Effect of time in culture on the suitability of two novel-association pyralid hosts for Cotesia sesamiae (Hymenoptera: Braconidae) development

The suitability of two New World pyralids Diatraea saccharalis and D. grandiosella for development of a South African population of the Old World braconid Cotesia sesamiae was studied for over 30 generations. These host-parasitoid combinations are novel associations. The C. sesamiae population was collected from Busseola fusca, reared for four generations on the novel host Chilo partellus, and for one generation in quarantine on another novel host D. saccharalis. Subsequent parasitoid generations were used for experiments. D. saccharalis was completely suitable, whereas D. grandiosella was only a marginally suitable host. Total numbers of parasitoid progeny that emerged from D. saccharalis increased over the first 13 generations, then declined by the 30th generation. Development time for C. sesamiae from egg to cocoon formation averaged 14.5-16.0 days and did not vary over time. D. grandiosella often encapsulated the parasitoid progeny, which did not decrease after rearing for multiple generations on Diatraea. Results suggest that before releasing a novel-association parasitoid into the field, there may be a benefit of rearing a parasitoid species on the target pest first; however, this benefit may be transient.