Evaluation of the potential of establishment of three introduced parasitoids of emerald ash borer (Coleoptera: Buprestidae) in Wisconsin

Three host-specific parasitoids have been released in North America as biological control agents of the emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). Yet, little is known about what factors contribute to the establishment of these parasitoids. We conducted releases of ~1500 Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae), ~1900 Spathius agrili Yang (Hymenoptera: Braconidae), and ~2700 Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) in Newburg, WI from June-September 2011. We also characterized woody vegetation, and signs and symptoms of A. planipennis on ash trees in this location during 2010, 2012 and 2013. In January of 2013 we felled trees to monitor for the establishment of parasitoids. We recovered a total of 41 T. planipennisi, indicating the establishment of at least one species of parasitoid. The incidence of signs and symptoms of A. planipennis increased over time. Our control plot had fewer signs and symptoms from 2010-2012, but was no different from our release plot in 2013. We found that Fraxinus nigra exhibited higher numbers of bark splits and epicormic shoots than Fraxinus pennslyvanica. No other differences between species of trees were observed. Significant relationships were found at the subplot level for exit holes by A. planipennis, bark splits and flecking, but their causes are unknown. We hope that the description of our infestation of A. planipennis, its associated signs and symptoms, and recoveries of biological control agents contribute to a better understanding of the factors that may play a role in a successful establishment by biological control agents against A. planipennis.