Minnesota expands wasp biocontrol program as emerald ash borer spreads to 60 counties
On Wednesday, Aug. 26, 2026, the Minnesota Department of Agriculture released about 8,000 parasitoid wasps into Ki-Chi-Saga Park in Chisago County as the emerald ash borer spreads across the state.[1]
Ki-Chi-Saga Park covers about 97 acres and is roughly 90 percent ash, leaving nearly the entire canopy vulnerable to emerald ash borer.[1] Most of the roughly 8,000 released wasps were placed as pupae and larvae in tree-mounted pull boxes and bark barrels.[1] The adult wasps are gnat-sized, native to Asia, parasitize emerald ash borer eggs and larvae, and do not sting people.[1] State entomologist Angie Ambourn said studies show the wasps can establish and persist for years after releases.[1] Local parks staff say the Ki-Chi-Saga canopy still has "a lot of green leaves," suggesting the biocontrol may be buying time even as long-term success remains uncertain.[1]
Emerald ash borer was first confirmed in Minnesota in 2009 after detection in St. Paul ash trees. The Minnesota Department of Agriculture began releasing USDA-reared parasitoid wasps in 2010 and expanded releases of immature stages in 2013. By mid-2025 the pest had been confirmed in 58 counties, and Fox 9 reports it has now reached 60 counties, threatening more than a billion ash trees across the state.[2] Since 2010 Minnesota has released more than 700,000 parasitoid wasps at 56 infested sites across 19 counties and tribal lands.
Aerial surveys mapped about 30,700 acres of rural forestland heavily impacted by emerald ash borer from central Chisago County through southeast Minnesota through 2024. A 2025 report found only two percent of Department of Natural Resources-managed ash stands were in areas considered generally infested by emerald ash borer.
The mainstream summary does not mention the significant context of the emerald ash borer's introduction to North America, which is attributed to wood packaging materials from Asia in the 1990s. This detail underscores the human role in the pest's spread, as it primarily disperses through human transport rather than natural means, with estimates suggesting it can spread hundreds of miles this way, compared to just half a mile to one mile naturally each year. Understanding this background is crucial for grasping the ongoing challenges in managing the pest and the urgency of Minnesota's biocontrol efforts. Additionally, while the summary highlights the release of parasitoid wasps, it does not address the broader implications of climate change, which research indicates is facilitating the northward expansion of invasive species like the emerald ash borer due to changing temperature and precipitation patterns. This connection emphasizes that the threat to Minnesota's ash trees is not just a local issue but part of a larger ecological shift influenced by climate factors.[3][4]
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📊 Relevant Data
Minnesota has released over 700,000 parasitoid wasps at 56 EAB-infested sites across 19 counties and tribal lands since the biocontrol program began in 2010.
Emerald Ash Borer Updates for Minnesota — Minnesota Department of Agriculture
Aerial surveys mapped 30,700 acres of rural forestland heavily impacted by emerald ash borer from central Chisago County through southeast Minnesota through 2024.
2025 Forest Health Annual Report context in DNR documents — Minnesota Department of Natural Resources
Only 2 percent of DNR-managed ash stands are in areas considered generally infested by emerald ash borer.
2025 Forest Health Annual Report context in DNR documents — Minnesota Department of Natural Resources
📌 Key Facts
- On Wednesday, August 26, 2026, the Minnesota Department of Agriculture said it has released about 8,000 parasitoid wasps into Ki-Chi-Saga Park in Chisago County over the past two years as part of the emerald ash borer response (Minnesota Department of Agriculture).
- Ki-Chi-Saga Park is roughly 97 acres and about 90% ash trees, leaving nearly the entire canopy vulnerable to emerald ash borer (Ki-Chi-Saga Park).
- Most of the released wasps are in pupal and larval stages kept in pull boxes and bark barrels on trees; the released gnat-sized adults are native to Asia, parasitize emerald ash borer eggs and larvae, and do not sting humans (gnat-sized adults).
- State entomologist Angie Ambourn said studies show the released wasps are establishing and persisting for years after releases at some Minnesota sites (State entomologist Angie Ambourn).
- Local parks staff report the Ki-Chi-Saga canopy is still holding with “a lot of green leaves,” suggesting the biocontrol may be buying time even though long-term success remains uncertain (Ki-Chi-Saga canopy).
📰 Source Timeline (2)
Follow how coverage of this story developed over time
- Minnesota Department of Agriculture has released about 8,000 parasitoid wasps into Ki-Chi-Saga Park in Chisago County over the past two years as part of the emerald ash borer response.
- Ki-Chi-Saga Park is roughly 97 acres and about 90% ash trees, making nearly the entire canopy vulnerable to emerald ash borer.
- Most of the released wasps are in pupal and larval stages housed in pull boxes and bark barrels on trees; adults are gnat-sized, native to Asia, parasitize EAB eggs and larvae, and do not sting humans.
- State entomologist Angie Ambourn says studies show the wasps are establishing and persisting for years after releases at some Minnesota sites.
- Local parks staff report the Ki-Chi-Saga canopy is still holding with “a lot of green leaves,” suggesting the biocontrol may be buying time even though long‑term success is still uncertain.