The Minnesota Department of Agriculture is releasing stingless wasps in Winona to try to control the spread of the invasive emerald ash borer.
Ash borer biocontrol coordinator Jonathan Osthus tells Winona Daily News that another batch of wasps is due for release this week.
The wasps are natural predators of the tree-killing insect found in Winona in April. They eat the bug or use ash borer larvae to incubate their eggs.
Tens of thousands of wasps have been released at sites infested with the ash borer over the past several years, including Great River Bluffs State Park and La Moille.
The ash borer was first found in Minnesota in 2009. Winona treated about 930 publicly owned ash trees with insecticide in 2012 in anticipation of the ash borer's spread.