With the help of a parasitic fly, a group of Massachusetts scientists is declaring victory over the leaf-munching, tree-damaging winter moth caterpillar.

Winter moth larva, which feed on tree leaves, blueberry crops and orchards, have been responsible for the defoliation of tens of thousands of acres along the New England coast each year since the early 2000s.

But entomologists at UMass-Amherst now say the winter moth population is decreasing to non-pest levels thanks largely to the introduction of a parasitic fly native to Europe. The pest-reduction approach, known as “biological control,” is expected to save Massachusetts residents millions of dollars in future pesticide costs, according to researchers.

“After 14 years of effort, we have successfully converted winter moth, a major defoliation invading Eastern New England, into a non-pest, presumably on a permanent basis,” Joseph Elkinton, an entomologist at UMass-Amherst, said in a statement. “We have averted what was shaping up to be another major invasion calamity for the entire United States comparable to gypsy moth.”

Elkinton, along with entomologists George Boettner and Hannah Broadley, has been working toward this goal for years. In 2005, the group started collecting the flies, which prey specifically on the winter moth, and grew them in a controlled UMass lab.

The flies were released at 44 sites along the Massachusetts coast, and the researchers have verified the flies have successfully populated in at least 38 of the locations.

The pest-reduction effort mirrors a biological control approach that succeeded in Nova Scotia and British Columbia, Canada, where the winter moth was found prior to invading the United States. The species is originally from Europe.

Elkinton said the biological approach, which is common in fighting invasive pests around the world, is working especially well here.

″(It’s) quite rare, at least on forest trees,” he said. “In fact, I can’t think of any other example involving a major forest insect in North America.”

The flies do not prey on anything besides the winter moth, according to the researchers. And while the approach will not wipe out the winter moth entirely, it will greatly reduce the invasive species.

“The object of biological control is to reduce density of the invasive species to non-pest status,” Elkinton said. “That is what we believe we have achieved.”