BENNINGTON -- After completing Vermont's largest bumble bee survey, biologists say about a quarter of the 15 different bee species found in the state have been severely diminished or are gone altogether.

Conservation biologist Kent McFarland, of the Vermont Center for Ecostudies, said in an interview Wednesday that his group conducted the state's most comprehensive bumble bee survey over the course of 2012 and 2013 and determined that three bumble bee species, one being the formerly common "rusty-patched bumble bee," appear to be extinct in the state.

He said these bees are represented in a collection at the University of Vermont, and as far back as the early 1990s, UVM entomology classes had no trouble collecting some of the now rare, or missing, species.

As for the total bumble bee population itself, it cannot be said whether it is up, down, or the same as this survey is the first statewide effort to sample them. If another study is done, only then will there be numbers to compare for total populations.

Still, the loss of bumble bee species is of concern.

"We're losing bumble bees even before we fully understand their benefits to our economy and well-being," McFarland said in a release.

Bumble bees are high class pollinators, he said. The way they vibrate their wings spreads more pollen than a honey bee or bird. Bumble bees are raised in captivity and sold to hothouse owners who use them to pollinate tomatoes, blueberries, and other crops.

Raised bumble bees from Europe may have introduced an intestinal parasite to native bumbles. McFarland said of the collected bees tested for the parasite, many tested positive, especially the yellow banded bumble bee, which showed a 70 percent infestation rate. The parasite drains the bee's energy and cuts back on its ability to produce honey for its colony. This is one possible reason for the decline, another is "neonicotinoid pesticides," pesticides with a nicotine base that bumble bees are particularly vulnerable to.

McFarland said these pesticides, if used improperly -- perhaps by spraying them on a flowering tree -- thousands upon thousands of bumble bees can be killed in a short period of time.

The survey divided the state into grids, McFarland said. It was not possible to search each one, but biologists from VCE and elsewhere collected bumble bees from roadside locations, specific habitat zones, while volunteers collected them from around their homes and gardens. He said some bumble bee species can be identified with the naked eye, but most require a microscope as the differences between them can be as small as the type of mouth parts.

McFarland said the dwindled species are being recommended for listing as endangered or threatened to the state of Vermont and to the federal government as well, for the bees are not unique to the state but range between Canada and the Midwest. They are on the decline all over, he said, but the hope is that pockets of resistant bumble bees can be found and their resistant genes used in breeding.

He said the data from the study has yet to be fully analyzed. Despite being limited in scope, it cost $40,000. The VCE is a nonprofit, receiving half its funds from donations and the other from government contracts and grants.

The VCE has conducted similar surveys in the past for birds and butterflies.

Contact Keith Whitcomb Jr. at kwhitcomb@benningtonbanner.com or follow him on Twitter @KWhitcombjr.