Chainsaws buzzed in the 200 and 300 blocks of Bartram Road in Riverside last week as a crew hired by the village took down a half dozen mature ash trees, more tangible evidence that the emerald ash borer is eating its way through the village.

Last week, Village Forester Michael Collins confirmed at least two more trees infested by the pest, which first showed up in traps in 2010. In December 2011, two emerald ash larvae were found inside the branch of a tree at Repton and Southcote roads.

The discovery resulted in the removal of several ashes in vicinity of the infested tree at Repton and Southcote, but that ash remained the only known tree in the village infested by the insect.

But earlier this summer, Collins said he found evidence of the emerald ash borer in a tree on South Delaplaine Road near Harrington Park, an area where ash trees are relatively numerous. That tree remains standing although it is scheduled for removal soon.

And last week, Collins said, a contractor working for the U.S. Army Corps of Engineers confirmed evidence of the emerald ash borer in an ash tree in Swan Pond Park, where several trees of multiple species are being removed for the regrading project that’s part of the Hofmann Dam removal effort.

“In 2012 we started finding it in traps, in 2011 we found it in one tree and now we’re starting to see it spreading to other quadrants,” said Collins. “It’s pretty much dead-on with the progression of the bug.

“What’s going on is that we have an infestation problem of an invasive pest introduced into the states. We’re just reacting to a problem we were given.”

Residents in areas around Swan Pond and Harrington parks who have ash trees on their parkways should soon receive letters informing them of the village’s policy regarding ash borers. The letter lays out three options.

They can wait until the ash tree becomes infested, at which time the village will take it down at the village’s expense; the homeowner could ask the village to take the ash tree down pre-emptively; or the homeowner could seek to treat the ash tree at his own expense.

The emerald ash borer is native to Asia and probably arrived on our shores on cargo ships or airplanes in solid wood packing material, according to the website www.emeraldashborer.info, created by the U.S. Department of Agriculture’s Forest Service, Michigan State University, Purdue University and Ohio State University as a clearinghouse for information on the pest.

The insect has killed tens of millions of trees in the United States and Canada since it was discovered in Michigan in 2002. It made its appearance in Illinois in 2006.

Collins said the drought the area has experienced this summers has accelerated the spread of the ash borer in Riverside. Many ash trees which appeared healthy just a year ago have started to show significant flagging, said Collins, a symptom of an emerald ash borer infestation.

“It’s a hard insect to detect until you see a lot of symptoms,” Collins said. “We’re seeing a lot of die-back on ash trees, which is leading me to believe it’s throughout the entire town.

“It’s definitely moving more quickly than I initially thought.”

The tree removals on Bartram Road last week – which included the loss of one specimen at least 4 feet in diameter at its base – were in response to the kind of die-back Collins has begun to see.

To date in 2012, Riverside has removed 63 trees, 24 of which have been ash trees and 17 of which have been elms. Collins noted that of the trees removed this year, 65 percent have been the result of an infestation by an invasive species.

“The majority of those removed were related to invasive, non-native insects,” said Collins, who noted that more ash trees are likely to come down through the end of the year.

“My mentality is to remove as much as funding allows,” he said. “I’m trying to get ahead of the insect.”

But “getting ahead” is a relative term, Collins indicated. Removing trees as soon as they start showing signs of infestation can help manage the pest long-term.

However, “long term in emerald ash borer terms is three to five years,” Collins said.