LAUSR

Abstract Previous studies have documented that parasitoids introduced to North America for biological control of emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), are establishing and persisting. However, no study has explicitly assessed their dispersal capabilities. In 2013 and 2014, we released Spathius agrili Yang (Hymenoptera: Braconidae), Tetrastichus planipennisi Yang (Eulophidae), and Oobius agrili Zhang and Huang (Encyrtidae) at 5 km intervals along 20 km of an ash (Fraxinus spp.) corridor, along which EAB was spreading. From 2013 to 2017, we deployed yellow pan traps every 250 m to detect parasitoid dispersal along the corridor; traps were checked weekly throughout the summer. In 2014, 2015, and 2016, ash health data were collected at each trap location. In 2016, additional traps were established parallel to the study area to detect dispersal away from the corridor. EAB were recovered in traps each year of the study and severity of ash decline aligned with EAB trap detections to indicate build-up and movement of EAB populations. Tetrastichus planipennisi were first recovered in 2014 and trap recoveries increased each subsequent year of the study. The other parasitoid species were not recovered. In 2016, T. planipennisi were detected ∼10 km from release points, established in areas with high EAB population densities, and were detected in traps ∼3.9 km away from the corridor. By 2017, T. planipennisi were recovered along the entire study area. This study quantifies dispersal of T. planipennisi and suggests it will be an important biological control agent of EAB in North America.