Hyperparasitism by an exotic autoparasitoid: secondary host selection and the window of vulnerability of conspecific and native heterospecific hosts

Encarsia transvena is an 'autoparasitoid' in the hymenopteran family Aphelinidae. In this species, female eggs are laid in whitefly nymphs. Male eggs are laid externally on immature parasitoids enclosed within the whitefly integument, either their own species, or other primary parasitoids. We explored parasitism by E. transvena of conspecific female immatures and those of a native primary parasitoid, Eretmocerus eremicus, in laboratory experiments. In the first experiment, female E. transvena were offered different combinations of two stages of E. transvena (late larvae – prepupae (ET2), and early pupae (ET3)), and one stage of E. eremicus (prepupae – early pupae (EE2)) in paired choice tests. The results indicated very little parasitism of ET3 relative to the host it was paired with, either EE2 or ET2. However, when EE2 was offered with ET2, there was no statistically significant difference in parasitism. In a no-choice experiment in which oviposition patterns and male progeny development were examined in four stages of both species of wasp, clear differences were observed between the host species. Only one stage of E. transvena (ET2) was parasitized and supported development of male E. transvena to any significant degree. In contrast, in E. eremicus, EE2, EE3 (red-eyed pupae), and EE4 (late pupae) were all parasitized, and male E. transvena emerged from all three stages, although fewer males emerged from EE4. In both species, wasp larvae that were still enclosed within the wet whitefly remains (ET1 and EE1) were parasitized at a very low rate. Lastly, an experiment that determined the length of the later developmental stages of E. transvena and E. eremicus suggested that the duration of the period in which E. transvena is susceptible to parasitism by conspecific females is less than half the period of susceptibility of E. eremicus. These results taken together suggest the potential for interference of E. eremicus by E. transvena, but other factors not examined here may also influence the outcome of interactions in the field.