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Home > Plants, Pests & Pest Control > Pest Management > Emerald Ash Borer Program > EAB Biocontrol > Recoveries

Recovery of EAB biological control agents in Minnesota


  • Tetrastichus planipennisi was recovered at multiple locations in Great River Bluffs State Park in southeastern Minnesota as well as Ft. Snelling State Park in the Twin Cities. These finds show that T. planipennisi survive an extremely cold winter and are establishing and reproducing. These wasps were found by peeling branches and logs and examining them for wasps, dissecting EAB larva and deploying yellow pan traps. 
  • Oobius agrili was recovered from Great River Bluffs State Park and Ft. Snelling State Park. EAB eggs were collected from bark samples then examined for evidence of parasitism. This detailed presentation showing how to look for Oobius agrili (PDF: 2.89 MB / 52 pages).

Parasitoid recovery methods:

  • Tree Debarking – This method of parasitoid recovery is the most labor intensive and requires the felling of branches or entire trees. Bark is removed in thin layers down to the cambium where EAB larval galleries and intact larvae are documented, collected and examined for evidence of parasitism.
  • Larval Dissection – A method used in conjunction with tree debarking. All intact EAB larvae with no outward signs of parasitism are collected during the process. Larvae are then dissected under a microscope to look for internal immature wasp larvae. The rear end of the insect is removed with a surgical scissors and the innards are pushed out into droplets of water. If the EAB larva is parasitized, the wasp larva(e) will float to the surface.
  • Bark Sifting –This method was devised by Dr. Leah Bauer with the USDA Forest Service Northern Research Station in Lansing, MI. A 10 x 50cm section of outer bark is scraped off the trunk of an infested ash tree using a drawknife. The bark is collected by a plastic sheet laid at the base of the tree and then transferred to a paper bag to dry out and avoid the growth of mold while in storage. After the bark has dried for a month, the sample is placed into a sieve and shook for two minutes. Once done sieving the sample, the fine debris is transferred to a ceramic dish and analyzed underneath a dissecting microscope for the presence of parasitized EAB eggs.
  • Yellow pan trapping – A method used to collect adult parasitoids by use of pan traps. Yellow bowls are affixed to the trunks of ash trees with shelving brackets and filled with a clear propylene glycol solution. This liquid traps insects that are attracted to the yellow color of the bowl. Traps are sampled weekly throughout the summer. Samples are poured through a filter, frozen and screened for parasitoids in the late fall.
Yellow starthistle seedlings
Minneapolis Parks and Recreation Board arborist collecting branches for sampling
Yellow starthistle plants
Branches are peeled then examined
Yellow starthistle seedhead
Data on EAB larvae, their galleries and evidence of parasitism are collected
Yellow starthistle infestation (Image credit: Steve Dewey, Utah State University, Bugwood.org)
Immature Tetrastichus planipennisi in an EAB gallery
Yellow starthistle rosette
Collecting bark samples
Yellow starthistle flower and seedheads
Bark samples are sieved
The basal rosette leaves of yellow starthistle are deeply lobed.
Bark samples are examined to look for EAB eggs
There are 2 types of yellow starthistle seed. Most seed produced has the white, fluffy hairs (Image credit: Cindy Roche, Bugwood.org).
Parasitized EAB egg with the developing Oobius agrili visible inside

MDA Contact

Chris Mallet, EAB Biological Control Coordinator

Jonathan Osthus, Project Manager

Plant Protection Division