Abstract
Over the last 9 yr USDA-approved introductions of the pathogen Ovavesicula popilliae (Microsporidia: Ovavesiculidae) were made in 8 US states for long-term biological control of Japanese beetle, Popillia japonica (Newman) (Coleoptera: Scarabaeidae). At least two additional states are redistributing pathogen-infected beetles to new sites within their state. As this effort continues, it is important to confirm the results of the original host-specificity research and to broaden the search for host species. In 2021 and 2022, we collected beetles at 7 sites in Michigan where Japanese beetles were heavily infected by O. popilliae. A total of 18 species of Coleoptera, including the Japanese beetle, were collected. DNA was extracted and analyzed individually for each of 10,977 beetles. Based on the observed incidence of infection, none of the 18 species of Coleoptera, other than the Japanese beetle, are likely to be adversely impacted due to the presence of O. popilliae. A few individuals of 3 of 18 species, all scarabs, became infected by O. popilliae (Ct value < 32.06): oriental beetle (Anomala orientalis [Waterhouse]), northern masked chafer (Cyclocephala borealis Arrow), and Asiatic garden beetle (Maladera formosae [Brenske]). These three species together had a combined mean infection rate of 0.7% ± 0.2% in 2021 and 5.1% ± 1.7% in 2022, compared with 43.1% ± 8.6% and 55.0% ± 8.9%, respectively, for Japanese beetle in 2021 and 2022. Disease development in these three species was poor, with the mean quantity of O. popilliae DNA detected per infected beetle being < 2.0 % the amount found in infected Japanese beetles at the same sites.