The role of biocontrol of Emerald Ash Borer in protecting ash regeneration after invasion

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

Submitted to: The Role of Biocontrol of Emerald Ash Borer in Protecting Ash Regeneration after Invasion
Publication Type: Book / Chapter
Publication Acceptance Date: 12/15/2017
Publication Date: 12/29/2017
Citation: Duan, J.J., Van Driesche, R.G., Bauer, L.S., Reardon, R., Gould, J., Elkinton, J.S. 2017. The role of biocontrol of Emerald Ash Borer in protecting ash regeneration after invasion. FHAAST-2017-02. Morgantown, WV: U.S. Department of Agriculture, Forest Service, Forest Health Assessment and Applied Sciences Team. 10 p. [brochure]. Available: https://www.nrs.fs.fed.us/pubs/55562

Interpretive Summary:

Technical Abstract: Emerald ash borer (EAB) is an invasive Asian beetle that is destroying ash in forests over much of eastern North America because of the high susceptibility of our native ash and a lack of effective natural enemies. To increase mortality of EAB larvae and eggs, the USDA (FS, ARS and APHIS) is carrying out a biological control program based on importation of parasitoids from the beetle’s native range in northeastern China and the Russian Far East. Four such parasitoids (Oobius agrili, Tetrastichus planipennisi, Spathius agrili and S. galinae) have been approved for release since 2007, and these species are being reared at the USDA APHIS EAB Biocontrol Facility in Brighton, Michigan, for release in the United States. Three of these natural enemies (O. agrili, T. planipennisi, and S. agrili) are now established at various locations and are helping lower EAB densities. In this technical brochure, we first reviewed the premise underlying the EAB biocontrol program and provided the most recent up-to-date progress that has been made since the initial introduction of the Asiatic parasitoids to the U.S. We know that in Asia, parasitoids cause high mortality of EAB, while in North America our native parasitoids only sometimes do so. While American ash are less resistance than Asian ash, North American ash can tolerate some level of EAB attack. Conversely, woodpeckers, which are scarce in northeastern Asia, are common in North America and kill about 30-50% of surviving large EAB larvae. The goal of the EAB biocontrol program is to lower survival of EAB eggs and larvae by establishing more effective Asian parasitoids. The combination of these introduced parasitoids, together with moderate levels of tree resistance, high woodpecker predation, and some attack by native parasitoids, will reduce EAB densities and lower the number of attacks per tree to levels that ash trees can survive. This lower attack rate is already happening at Michigan study sites and is allowing ash saplings (1-2 inch diameter) and young ash (5-8 inch diameter) to survive and produce seed for ash regeneration. We have made considerable progress over the last ten years documenting the impacts of these factors, as described below. Moreover, in the aftermath of EAB in southeast Michigan forests where T. planipennisi is protecting young ash, recruitment and growth of native hardwoods are favored over invasive species. Based on (1) our work during the past 10 years in Michigan and 3 years in the northeastern United States, (2) the likely imminent spread of EAB to the South and West, and (3) the species of ash in those non-yet-invaded areas, we expect (a) that the newest larval parasitoid, Spathius galinae, recovered in 2017 in all 6 of our release plots in CT, MA, and NY, will establish and spread quickly in the northeastern United States. (b) that small ash (1 to 8 inch diameter), now and in the near future, will be protected by O. agrili and T. planipennisi, allowing ash regeneration in the northeastern and central United States. (c) that within 5-10 years, as current young ash reach mid-size (9-15 inch diameter), S. galinae will be abundant and able to protect these trees as they enter the mid-size cohort, allowing ash regeneration and regrowth to continue. In addition, our findings indicate that the newly EAB-invaded regions in the U.S. may need different parasitoids. States just now being invaded in the South (Louisiana and nearby states) or likely to be invaded soon in the West (California through Oregon) and Southwest (Arizona and nearby states) may need different Asian parasitoids (due to climatic differences between these states and northeastern China or the Russian Far East, the source of the parasitoids we are now releasing). Efforts to find and collect EAB parasitoids in southern and western China are needed.