Speciation in the Encarsia pergandiella complex (Hymenoptera: Aphelinidae): modeling the effect of Cardinium-induced cytoplasmic incompatibility and hybrid incompatibilities.

Encarsia pergandiella (Hymenoptera: Aphelinidae) is a species complex of important parasitoids of whiteflies that differ in reproductive mode and endosymbiotic bacteria infection. Whereas E. pergandiella from California appears uninfected, the endosymbiotic bacterium Cardinium causes thelytoky in a population from Brazil, and cytoplasmic incompatibility (CI) in a sexual population of from Texas. E. pergandiella from California and Texas have morphological differences, and show partial to complete reproductive isolation from each other, in spite of genetic distinctiveness. Here we first evaluated the role of the CI-inducing endosymbiont Cardinium and genetic incompatibilities in the reproductive isolation and competitive interactions of these parasitoid populations. The level of reproductive compatibility between Cardinium-infected and uninfected E. pergandiella was assessed by both pre-zygotic (mating preferences) and post-zygotic (crossings) experiments. Then the results were used to develop a theoretical model to predict the outcome of secondary contact of the two allopatric species in cage experiments.