| Bacteria in the genus Wolbachia are Rickettsial intracellular parasites of arthropods. The effects of Wolbachia infection in several insect species were investigated in two species of fruit flies, Drosophila sechellia and D. mauritiana, as well as the beetle Diabrotica virgifera virgifera and several species of crickets in the genus Gryllus. Cytoplasmic incompatibility was expressed partially in D. sechellia and fully in D. v. virgifera, but not in D. mauritiana. It was determined that the lack of cytoplasmic incompatibility in D. mauritiana results from a difference in the bacterial strain harbored by this species of fly.; Populations of D. v. virgifera sampled throughout the corn belt were found to be infected with the same strain of Wolbachia, with the exception of two populations in Arizona. Matings between tetracycline-treated D. v. virgifera and its subspecies D. v. zeae showed that removal of the infection from the former eliminated the mating incompatibility that had previously been demonstrated between these two subspecies.; With the exception of Gryllus firmus all other members of the genus Gryllus tested were found to be infected with Wolbachia. Gryllus rubens was found to be infected with a strain different from that found in G. integer and G. pennsylvanicus. However, specimens from the Davis, CA and Las Cruces, NM populations of G. integer were infected with both rubens- and integer-type bacteria and some individuals in Las Cruces, NM were doubly infected with both. G. pennsylvanicus populations in nearly all localities sampled on the northeastern American continent, as well as a population in Farina, IL, were found to be infected with the pennsylvanicus- and rubens-type strains, and as in G. integer some individuals were doubly infected with both strains of bacteria. Based on the incompatibilities previously reported between these species of Gryllus, as well as the degree of difference at the level of the cell division ftsZ gene between the strains of Wolbachia they harbor, we predict that the integer-, pennsylvanicus- and rubens-type strains are bidirectionally incompatible. Wolbachia may have played a role in determining the degree of hybridization between the various Gryllus species and in this manner affected their speciation. |
