The three species of parasitoid wasps released in Minnesota (Tetrastichus planipennisi, Spathius galinae and Oobius agrili) are reared in a specialized USDA facility in Michigan. They are provided at no charge to state cooperators such as the Minnesota Department of Agriculture to release. A fourth species, Spathius agrili, was released in Minnesota from 2010 – 2012. Releases of S. agrili were discontinued for northern regions because this species was unlikely to establish.
We initiated releases in 2010 in southeastern Minnesota with adult parasitoids. To increase the efficiency of parasitoid rearing we began receiving and releasing immature stages of the parasitoids in 2013. They are in protective structures that are placed in the field then the adult wasps emerge within the next few weeks. There are now over 40 release sites in EAB infested areas of Minnesota. Releases at new and select existing sites will continue. View locations of EAB finds and biocontrol agent releases.
Biological Control Releases in Minnesota
| Biocontrol agent | 2010 | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2020 | 2021 | 2022 | 2023 | All |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Tetrastichus planipennisi | 2,154 | 19,480 | 19,822 | 42,579 | 34,434 | 151,022 | 45,130 | 43,245 | 27,310 | 34,607 | 4,062 | 3,030 | 9,039 | 5,520 | 438,283 |
| Oobius agrili | 0 | 3,641 | 10,241 | 8,597 | 12,062 | 31,490 | 42,300 | 23,100 | 12,600 | 8,400 | 8,320 | 2,200 | 5,400 | 4,800 | 173,151 |
| Spathius galinae | 0 | 0 | 0 | 0 | 0 | 0 | 1,613 | 2,151 | 4,663 | 4,609 | 4,438 | 2,809 | 5,894 | 4,937 | 31,114 |
| Spathius agrili | 1,172 | 7,596 | 15,258 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 27,177 |
| Totals | 3,326 | 30,717 | 45,321 | 51,176 | 46,496 | 182,512 | 89,043 | 68,496 | 44,573 | 47,616 | 16,820 | 8,039 | 20,333 | 15,257 | 669,725 |
How Biological Control is Implemented
Not all sites fit the criteria for biological control. Once an EAB infestation is identified, several steps need to be completed to determine if biological control is viable:
- Perform a delimit survey of the infestation to identify the perimeter of where symptoms are visible.
- Gauge the intensity or pest pressure in the area based on severity of EAB symptoms throughout the identified visibly infested area. Low to moderate EAB densities are recommended for potential sites.
- Identify forested areas on public or private land within the visibly infested area where removal and/or treatment of infested ash trees will not be feasible. Size and composition of forest should be at least 40 acres and at a minimum include 20 percent ash of varying size class. Ideally, the site would be greater than 25 percent ash and connected to other woodlots.
After a viable biological control site is identified, coordination by the MDA with local natural resource managers, property owners and the USDA EAB Parasitoid Rearing Facility are necessary. At each site one has to obtain permission, guarantee access and ensure other management objectives won’t interfere with implementation. Special permits may be necessary depending on the ownership and designation of land. Long term site access is important for follow-up monitoring of ash health and documenting parasitoid establishment.
