NORTHBOROUGH — After keeping honeybees for more than 15 years, Mary Duane has learned to recognize the telltale signs of a “pesticide kill.”

Duane, president of the Worcester County Beekeepers Association, said maintaining the health of her bees has grown more difficult each year since she picked up the hobby in 1999.

While a variety of ailments can afflict bee colonies, from parasitic mites to diseases and dry weather, Duane said pesticides are increasingly responsible for bee fatalities. Duane said she sometimes finds multiple generations of bees — middle-aged, younger and older — lying dead at the entrance of the hive.

In other instances, bees are exposed to low levels of pesticide over a longer period of time, Duane said, sapping their ability to fight off mites, which have become ubiquitous in the state.

“It’s really, really tragic,” said Kathy deGraaf, a Northborough beekeeper who has also encountered pesticide kills in Worcester County.

“Bees are out in the daytime,” deGraaf said, “and if a farmer is spraying in the daytime and bees are visiting that crop that's been sprayed, they’re going to pick up whatever is on the flowers and they’re going to bring it back to their hive, and then what you see is a really big pile of dead bees."

Environmentalists and beekeepers have been rallying around a bill designed to curb and track the use of a common pesticide they believe is destroying bee populations, which have declined rapidly in recent years.

Nationally, beekeepers lost about 44 percent of their hives last year, according to the U.S. Department of Agriculture. In Massachusetts, beekeepers lost 46 percent of their colonies.

A class of pesticides known as neonicotinoids, many beekeepers say, is detrimental to populations of bees and other pollinating insects. The pesticide, which became used more widely in the 1990s and 2000s, is common in commercial farming operations and backyard lawn care products. Many commercially available seeds, including corn and soybean seeds, are often treated with neonicotinoid coatings.

State Rep. Carolyn Dykema, D-Holliston, has sponsored a bill that would only permit neonicotinoids to be applied by people who have completed a certification program. Additionally, the proposal, known as “An Act Protecting Massachusetts Pollinators,” would require that stores label plants that have been treated with neonicotinoids.

The bill is currently in the House Ways and Means Committee after receiving a favorable recommendation from the Legislature’s Joint Committee on Environment, Natural Resources and Agriculture.

“It certainly has more traction than it’s had up to this point,” Dykema said of the bill, “and the press is giving it a lot more attention.”

Statewide, officials have increased their efforts to recognize the importance of honeybees and other pollinators, which are essential to the production of many foods.

Gov. Charlie Baker recently declared June 20-26 as “Massachusetts Pollinator Week.” Last month, the Department of Agricultural Resources also celebrated the opening of the first state apiary at UMass Amherst.

Lawmakers outside Massachusetts have moved to regulate certain pesticides, too. In April, Maryland adopted a law to eliminate consumer use of neonicotinoid products, and Connecticut passed similar legislation weeks later. The European Union has also banned the use of certain neonicotinoids.

The U.S. Department of Agriculture has not recommended a similar ban. A USDA-sponsored study in 2015 concluded neonicotinoids are not likely the sole cause of bee colony collapses, and some other studies have reached mixed conclusions.

A survey conducted over the past year by the USDA concluded that Varroa mites were the leading stressor of large beekeeping operations nationwide, though pesticides also influenced colony health.

In Massachusetts, for example, beekeepers with five or more colonies who participated in the survey reported that between April and June, when agricultural activity is at its peak, more than 60 percent of their colonies faced duress from pesticides. A similar proportion were afflicted by mites, parasites and other pests.

“At this point, it’s not debated that these pesticides have a negative impact on the bees,” Dykema said. “The real question is at what level do they have a lethal impact on bees.”

Farmers and beekeepers have yet to reach agreement on that question, sparking passionate responses from both sides.

Ed Davidian, president of the Massachusetts Farm Bureau Federation, said it should be the responsibility of the state’s Pesticide Board, and not the Legislature, to determine which chemicals are safe to use. Davidian, co-owner of Davidian Farm in Northborough, said lawmakers don’t have the scientific expertise to properly evaluate the danger posed by specific pesticides.

“It should not be a political decision,” he said.

While he acknowledged that pesticides can be harmful to bees, Davidian said farmers can limit the potential harm by learning to more narrowly apply products to their crops. For instance, farmers can spray pesticides during times of the day when bees are less active.

Davidian added that colony collapse can’t be explained by pesticides alone, and that some hobbyist beekeepers are reluctant to treat their colonies for mites and other threats, allowing them to proliferate. Bees and humans alike may also face greater harm if farmers switch from neonicotinoid products to more toxic pesticides, Davidian said.

"This whole thing of trying to blame it on the agricultural industry — the decline of bees — is not right,” he said.

Wicked Local Newsbank Editor Gerry Tuoti contributed to this report. Jim Haddadin can be reached at 617-863-7144 or jhaddadin@wickedlocal.com. Follow him on Twitter: @JimHaddadin.