Wolbachia is a maternally inherited, gram-negative bacterium and has been found to be associated with up to 60% of all insects, frequently resulting in male-killing, feminization, and cytoplasmic incompatibility in the hosts. Gall wasps and other gall-forming insects induce on various host plants abnormal tissue growths, or plant galls, with distinct morphology. They are considered as obligatory parasites to their host plant. The presence of Wolbachia infection in gall wasp populations in North America has not been extensively documented. Given the strong influence on host reproduction, not knowing Wolbachia infection in insect populations prevents the understanding of how populations are being affected in their dynamics and evolution. In this study, I collected from nine locations, within Illinois and Indiana, galls made by several gall wasp and other gall-making insect species. DNA extracted from the gall makers was amplified with a Wolbachia specific gene (wsp) to detect Wolbachia infection. This allowed me to assess the frequencies and patterns of Wolbachia infection in site and species of gall wasps and other gall-making insects in Illinois and Indiana. Of the 101 individuals sampled 31 (30.39%) tested positive for Wolbachia infection. Ten of 13 sampled species tested positive for Wolbachia infection with populations varying in infection rate with some populations having no presence of Wolbachia. These findings were among the first survey of Wolbachia infection in these species and locations providing a basis for further studies to monitor the impacts of Wolbachia infection on the populations dynamics and reproductive evolution
