Augmented establishment of <i>Ovavesicula popilliae</i> (Microsporidia) for biocontrol of Japanese beetle (Coleoptera: Scarabaeidae) in Colorado

Ovavesicula popilliae (Microsporidia: Ovavesiculidae) is a host specific, obligate pathogen of Japanese beetle (Coleoptera: Scarabaeidae, JB) that causes chronic disease and mortality of larvae, and reduced fecundity of surviving females. Ten sites in Colorado along the leading edge of the westward spread of JB across North America were inoculated in 2015 or 2018 by drenching a small area (200 m2) of turfgrass with solutions of O. popilliae spore vesicles made from macerated infected beetles. This paper reports infection rates in 2021 and 2022 at these sites plus 6 control sites added in 2020 or 2021 to evaluate the impact of inoculations. Infections were diagnosed by extracting DNA from 96 JB per site for qPCR analysis of O. popilliae DNA. A 4-fold greater infection rate in 2022 at inoculated sites compared with control sites is evidence that inoculations augment establishment of O. popilliae. Infection rates of JB at inoculation sites did not reach 1.0% for 3 to 6 yr following inoculations, most likely because the area inoculated is small (200 m2) while JB traps baited with pheromone plus feeding lure attract JB from a large surrounding area.