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Emerald ash borer (EAB) biological control uses parasitoid wasps to reduce EAB populations and is still experimental in practice. However, biological control is the only practical EAB management strategy for natural forest ash and is a component of urban EAB management. We will improve biological control implementation with the following:

Expand EAB biocontrol: Biological control was initiated in 2010 and biological control agents have been released at most known infestations. EAB is spreading so new detections are inevitable. The biological control effort will be expanded to address new EAB finds and continue existing site monitoring.

Assess EAB biocontrol establishment and impact: Measure numbers of stingless wasp recoveries. Annual data will allow us to examine how densities of biological control agents are changing through time (i.e., impacting population growth and mortality rates of EAB).

Determine cold tolerance: Measure the cold hardiness of Spathius galinae (new parasitoid wasp). This will be accomplished with techniques that our team successfully applied to two other biological control agents for EAB. This information refined MDA’s strategy to implement biocontrol for EAB.

Citizen engagement and Biosurveillance of EAB: Engage citizen scientist volunteers to monitor EAB populations statewide using a native wasp, the smoky winged beetle bandit. This harmless wasp specifically hunts metallic wood boring beetles (buprestids) including EAB as food for their offspring. Citizen scientists can survey the type of beetle prey the wasps are capturing and help with early detection of EAB if it is present in the area. Our goals are to better delimit EAB populations and educate the public about EAB. Additionally, biosurveillance will monitor for similar high risk wood-boring beetles that are not documented in Minnesota such as the European oak borer that threaten oaks. That borer was recently detected with biosurveillance in Ontario, Canada. More information on biosurveillance and Minnesota's Wasp Watchers Program.

Summary of Project Findings:

We are pleased to report that the effective implementation of EAB biocontrol has led to increasing recoveries of the larval parasitoid Tetrastichus planipennisi and the egg parasitoid Oobius agrili through time based on data analysis in Activity 2. We produced several peer-reviewed scientific publications (with full credit to LCCMR) on Activities 3 and 4. For Activity 3, we evaluated the cold hardiness of the larval parasitoid Spathius galinae and published a study forecasting its survival in North America (Wittman, Aukema, Duan, and Venette (2021) Forecasting overwintering mortality of Spathius galinae in North America. Biological Control. 160: 104694). The insect will survive best in areas where winter temperatures remain above -20 Fahrenheit. For Activity 4, we published two journal articles detailing a checklist of buprestids found in Minnesota (Hallinen, Steffens, Schultz, Aukema (2021) The Buprestidae (Coleoptera) of Minnesota, with a discussion of the emerald ash borer, Agrilus planipennis Fairmaire. The Coleopterists Bulletin 75: 173-190) as well as a study on their habitat features (Hallinen, Wittman, Aukema (2020) Factors associated with diversity and distribution of buprestid prey captured by foraging Cerceris fumipennis (Hymenoptera: Crabronidae) (Environmental Entomology 49: 1363-13763). These works provide critical information on what is here, now, so we have a basis of comparison for when a new invasive wood-boring beetle in the same family as emerald ash borer arrives in the future. We then published, from the scientific checklist, a free and accessible guide (The Buprestidae of Minnesota) that can be downloaded from permalink https://hdl.handle.net/11299/218928. This latter guide contains not only specimen photos but also maps of the distribution record and dates of last collection by decade.

Affiliations:

1. University of Minnesota
2. USDA Forest Service
3. Minnesota Department of Agriculture

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:

1. Perform a delimit survey of the infestation to identify the perimeter of where symptoms are visible.
2. 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.
3. 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 must 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.