Differences in mating behaviour and sex ratio between three sibling species of Nasonia

Mating in Nasonia wasps has traditionally been thought to occur on or around their pupal fly host, after emergence. Here we report the occurrence of within-host mating (WHM) in Nasonia. Within-host mating is interesting as a simple behavioural trait that can have a strong effect both on the level of inbreeding and the level of interspecific mating in a species. A survey of WHM levels was performed on 17 recently collected strains of Nasonia from three sibling species: N. vitripennis, N. giraulti and N. longicornis. Both N. giraulti and N. longicornis mated within hosts at significantly higher rates than N. vitripennis. The mean ( plus or minus S.D.) percentage of females mating within hosts was 64.4 plus or minus 16.6 in N. giraulti, 9.1 plus or minus 8.5 in N. longicornis and 1.0 plus or minus 2.1 in N. vitripennis. Within-host mating in N. giraulti and N. longicornis may represent a mechanism for escaping hybridization with N. vitripennis, which often co-occurs microsympatrically in birds' nests with the other two allopatric species. Since WHM presumably increases local mate competition (LMC) and inbreeding among progeny, elevated levels of WHM should select for more female-biased sex ratios. Mean one-foundress sex ratios were calculated for 20 Nasonia strains, with most of these strains being the same as those in the general WHM assay. As expected, N. giraulti had significantly more female-biased sex ratios than both N. longicornis and N. vitripennis. The implications of WHM for the population dynamics of Nasonia are discussed.