The invasive woodboring beetle, the emerald ash borer (Agrilus planipennis) or EAB was first discovered in Wisconsin in 2008 at River Edge Nature Center in Newberg WI. From 2010 - 2013, myself and colleagues setup and surveyed plots of ash trees at River Edge to evaluate how rapidly the beetle would cause tree mortality in Wisconsin. In 2011 we released three species of parasitic wasps (Oobius agrili, Spathius agrili, Tetrastichus planipennisi) reared at a USDA biological control facility to determine: 1) if they would establish in Wisconsin and 2) if they would potentially slow the population growth of EAB. In our recent paper we discuss the results of this study. We found that over the four years the number of epicormic shoots, damage by woodpeckers, bark splits, and emergence holes of EAB, all signs and symptoms of the beetle, increased dramatically on our trees. We also saw large declines in the crowns of trees (the leafy top of the tree, often indicative of tree health). In some cases there were differences in damage between green and black ash by EAB. At the end of our study we felled trees to determine if the wasps we released had established in Wisconsin. We detected one species of wasp, T. planipennisi, but further sampling will need to occur to determine if the other two species established. Our work shows that forests in east/central Wisconsin are suitable for EAB and it contributes rapid mortality. Parasitic wasps may slow the growth of populations of EAB in Wisconsin in the future, but currently populations of these wasps remain at low levels.
Photo Courtesy of Wisconsin DNR. Mortality of ash trees caused by EAB at River Edge Nature Center, August 2013.