Evaluation of recovery and monitoring methods for parasitoids released against emerald ash borer

Emerald ash borer (Agrilus planipennis Fairmaire, EAB) is an invasive forest pest and the target of an extensive biological control program designed to mitigate EAB-caused ash (Fraxinus spp.) mortality. Since 2007, hymenopteran parasitoids of EAB from northeastern Asia have been released as biological control agents in North America, including Oobius agrili (Hymenoptera: Encyrtidae), an egg parasitoid; Tetrastichus planipennisi (Hymenoptera: Eulophidae), a larval endoparasitoid; and Spathius agrili (Hymenoptera: Braconidae), a larval ectoparasitoid. Following parasitoid releases in new locations, methods currently used to document presence and establishment and to monitor dispersal of parasitoids in the field were simultaneously evaluated, including destructive sampling of entire trees and deployment of egg sentinel logs (ESLs), egg sentinel cups (ESCs), larval sentinel logs (LSLs), and yellow pan traps (YPTs). All three parasitoids were recovered using YPTs and destructive sampling of trees. Spathius agrili was the only species to be recovered using LSLs, however, results indicate YPTs were as effective as LSLs. YPTs were also as effective as destructive sampling of entire trees for O. agrili and S. agrili detection. YPT trap catches were significantly associated with egg parasitism on sampled trees by O. agrili, but not for larval parasitoids. Additional research indicated YPTs are effective in recovering O. agrili and T. planipennisi at distances as great as 20 m from release points. It is therefore recommended that YPTs be used as the preferred method for parasitoid recovery as the other methods are much more labor intensive and prone to difficulties.