Natural Enemies of Emerald Ash Borer are Fighting the Good Fight in North America
Forest Service scientists are working closely with other U.S. Department of Agriculture and university researchers to monitor ash trees and emerald ash borer (EAB) for evidence of natural enemies that feed on EAB larvae and eggs. This long-term study takes place in six forested areas of Michigan where EAB natural enemies, originally from Asia, were first released in 2007. The study also includes six control sites where parasitoids were not released. By fall 2012, 88 percent of EAB-infested ash trees contained at least one brood of the larval parasitoid Tetrastichus planipennisi (Tets) throughout the 12 sites on average. Moreover, the average number of Tet broods increased from zero to three broods per tree. Average larval parasitism increased from zero to 21 percent at release sites and from zero to 13 percent at control sites. This demonstrates rapid range expansion and increasing abundance of Tets attacking EAB across the region of this study. Oobius agrili (Oobs), an EAB egg parasitoid, also was first introduced in 2007 at Michigan release sites. By fall 2011, Oobs were recovered from 45 percent of the ash trees with an average egg parasitism of 5 percent at release sites and less at control sites. The scientists expect these EAB natural enemies to play an important role in the management EAB in North America.
Forest Service Partners