Data from: Invasion dynamics of Wolbachia bacteria in laboratory populations of the wasp, Trichomalopsis sarcophagae (Hymenoptera: Pteromalidae)

Wolbachia are obligate intracellular bacteria common in diverse arthropod hosts.  Infections are spread from infected mothers to their progeny via egg cytoplasm.  Establishment and spread of infections are affected by the number of infected individuals invading the novel host population plus the effect of infections on the production of female progeny and mating behaviour.  Taking these factors into account, we examined the ability of Wolbachia to establish and spread in populations of the parasitoid wasp Trichomalopsis sarcophagae (Gahan) (Hymenoptera: Pteromalidae), a species for which the effect of Wolbachia infection on host reproduction has not been previously examined.  Experimental crosses showed that infections caused 100 percent cytoplasmic incompatibility (CI), wherein uninfected females mated with infected males (♀ x ♂^w) only produced male progeny and broods of smaller size.  All other mate combinations (♀ x ♂, ♀^w x ♂^w, ♀^w x ♂) produced normal broods of similar size and sex ratio.  The expression of this CI, however, has two forms.  Fertilized eggs from the incompatible cross either develop as though male, or fail to develop.  Mate-choice tests showed that females mated once and showed no preference for infected or uninfected males.  An experiment tracking the extinction or subsequent establishment and spread of Wolbachia infections in laboratory colonies for 20+ generations indicated an establishment threshold for infection prevalence of less than 10%.  The existence of such a threshold, and its relatively low value, is broadly consistent with a simple mathematical model informed by the results from the experimental crosses and mate-choice tests. This is one of few experimental studies tracking the spread of Wolbachia infection in an insect species.  It helps explain why Wolbachia is such a successful and widespread parasite.