ST. PAUL, Minn. (AP) - Minnesota officials are reporting success in the battle to slow the spread of emerald ash borers.

The Minnesota Department of Agriculture says it's confirmed that stingless wasps released in Great River Bluffs State Park near Winona two years ago are reproducing, which the department says is evidence that they're doing their job in attacking the destructive tree pests.

The wasps are part of a biological control effort. Since the emerald ash borer is not native to North America, it lacks natural enemies. The stingless wasps come from Asia, where emerald ash borers originated, and feed on ash borer eggs and larvae. The wasps don't attack humans.

Stingless wasps have also been released in Houston County in southeastern Minnesota and the Twin Cities in hopes of controlling other infestations.