A switch into an immunocompromised individual of a new host species is likely to be temporary and not lead to speciation unless the new parasite can better adapt to its new host, at the same time with minimal gene flow occurring with conspecifics from its ancestral host. Availability of populations of similarly immunocompromised new hosts that allow continued transmission and adaptation of the new parasite host could favor divergence from the founding parasite and speciation. Varroa mites (Varroa destructor ) in honey bees (Apis mellifera) suppress the activity of several immune-related genes (encoding both antimicrobial peptides and enzymes) and favor higher infection titers with the deformed wing virus (Yang and Cox-Foster, 2005) . Drosophila simulans infected with Wolbachia have reduced ability to encapsulate eggs of the parasitoid Leptopilina heterotoma (Fytrou et al., 2006) .