ST. PAUL, Minn. (AP) -

Minnesota is plotting its next steps in the fight to stop the spread of emerald ash borders.

The Minnesota Department of Agriculture says it's drawing on innovative research from the University of Minnesota and the U.S. Forest Service to attack the tree pests using their natural enemies -- stingless wasps that prey on emerald ash borers.

The Forest Service is studying how well the wasps, as well as emerald ash borers, tolerate cold winters. At the same time, university researchers are studying how far the stingless wasps can fly.

MDA Biological Control Coordinator Monika Chandler says the data will help officials determine how best to deploy the stingless wasps against ash border infestations.

Emerald ash borers have killed millions of trees since they arrived in North America in the 1990s.