The state agriculture department is finding that the weapon launched two years ago to combat emerald ash borer could be working.

The Star Tribune reports tiny parasitic stingless wasps, a native of China and a natural predator of the invasive beetle, were released in infested areas of Winona, Houston County and the Twin Cities.

Monika Chandler, Minnesota Department of Agriculture Biological Control Program Coordinator, says evidence collected in Winona this fall show the wasps are reproducing and attacking the ash borers. There's also evidence that the wasps are traveling, some found a half mile from their release sites, Chandler said.

North American ash trees have no natural resistance to the pests, which are also native to China, so infestation is always fatal to the tree, according to the Pioneer Press.

The emerald ash borer is regarded as a threat to Minnesota's nearly 1 billion ash trees.

In Minneapolis, a recently-approved tax levy will allow the city to take down 40,000 ash trees over the next eight years as part of a $9 million project to blunt the impact of the invasive pest.

Although the wasps are proving to be a successful weapon so far, they may not win the battle, the Pioneer Press points out. For now, agriculture officials just hope to slow the emerald ash borers' spread.