Progress and challenges of protecting North American ash trees from the Emerald Ash Borer using biological control

Authors: Duan, Jian; BAUER, LEAH - Us Forest Service (FS); VAN DRIESCHE, ROY - University Of Massachusetts; GOULD, JULI - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Forests
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2018
Publication Date: 3/15/2018
Citation: Duan, J.J., Bauer, L.S., Van Driesche, R.G., Gould, J.R. 2018. Progress and challenges of protecting North American ash trees from the Emerald Ash Borer using biological control. Forests. 9(3):142. https://doi.org/10.3390/f9030142.
DOI: https://doi.org/10.3390/f9030142

Interpretive Summary: The emerald ash borer (EAB) is a serious invasive forest pest that has killed tens of millions of ash trees in the United States and Canada. A biological control program was initiated against this destructive pest of ash trees (Fraxinus spp.) in 2007 after U.S. federal regulatory agencies approved release of three biocontrol agents (parasitic wasps) in EAB-invaded areas. Scientists from the ARS Beneficial Insects Introduction Research Unit in Newark, DE, the US Forest Service, and the University of Massachusetts discuss the rationale and ecological premises of the EAB biocontrol program and report on progress in North American ash recovery in southern Michigan where the parasitic wasps were first released. Two of the introduced biocontrol agents have established in many release areas and are suppressing EAB densities and protecting the regenerating ash saplings and young trees. To protect growing and surviving ash trees, however, more widespread releases of a new biocontrol agent (a parasitic wasp from the Russian Far East) are needed. This research contributes to the development of biocontrol-based, sustainable EAB management strategy.

Technical Abstract: After emerald ash borer (EAB), Agrilus planipennis Fairmaire, was discovered in the United States, a classical biological control program was initiated against this destructive pest of ash trees (Fraxinus spp.). This biocontrol program began in 2007 after federal regulatory agencies and the state of Michigan approved release of three EAB parasitoid species from China: Tetrastichus planipennisi Yang (Eulophidae), Spathius agrili Yang (Braconidae), and Oobius agrili Zhang and Huang (Encyrtidae). A fourth EAB parasitoid, Spathius galinae Belokobylskij (Braconidae) from Russia, was approved for release in 2015. We review the rationale and ecological premises of the EAB biocontrol program, and then report on progress in North American ash recovery in southern Michigan, where the parasitoids were first released. We also identify challenges in conserving native Fraxinus using biocontrol in the aftermath of the EAB invasion, and provide suggestions for program improvements as EAB spreads throughout North America. We conclude that more work is needed to 1) evaluate the establishment of biocontrol agents in different climate zones, 2) determine biocontrol impacts on native Fraxinus species in different regions, 3) expand foreign exploration for EAB natural enemies throughout Asia, 4) identify EAB-resistant ash genotypes, and 5) develop an area-wide approach to EAB management.