In July 2012, beekeeper Steve McDaniel peered into one of his most productive hives and saw healthy, busy honeybees. He and his wife left for a week’s vacation, confident they could begin collecting the honey after a break at the ocean.

When they returned, the bees were dead. The honey was gone. The few guard bees that remained alive were listless.

Over the next several months, colony after colony on his Carroll County farm succumbed. In all, he lost 13 of 20 colonies. In 35 years of raising bees, McDaniel had never seen anything like it.

“I was doing absolutely everything I could to keep that hive alive. And I just felt helpless,” said McDaniel, who owns McDaniel Honey Farm and the Beekeeper’s Bride line of candles and ornaments with his wife, Angie. “We were all just mystified. Nobody really knew what was going on.”

In 2012, Maryland beekeepers lost 60 percent of their bees, about twice the national average and far more than is typical in a year. Virginia lost 40 percent. Nationwide, the rate was almost 30 percent.

Bees are crucial for pollinating many of the crops we eat, including blueberries, nuts, onions, beets, watermelons and about 70 other plants. They’re so important that many a beekeeper makes a living taking the hive boxes filled with colonies of bees across the country to California in the winter so bees can pollinate the almond groves. Their decline has worried scientists and policymakers alike. They have termed the phenomenon “colony collapse disorder,” but they have yet to determine one main cause. Rather, research points to a variety of factors: increased pesticide use, lack of diversity in flowers, parasites, climate and weak queen bees.

McDaniel talked to other Maryland beekeepers whose bees were also dying. It had been a rough winter, but these bees were dying in the summer. The varroa destructor, a parasitic mite from Japan, has been killing American bees since the 1980s. But it wasn’t as though there had been a sudden influx of the mites in 2012. He saw no evidence of viruses. Some blamed the ethanol boom, which had taken millions of acres of land out of conservation and put them in corn, giving the bees fewer foraging options for nectar and pollen. But the ethanol boom began in 2005, and it didn’t make sense that the collapse would take seven years to develop.

What had changed, the beekeepers realized, was the abundance of a group of pesticides called neo-nicitinoids. These insecticides, manufactured by Bayer and sold in home improvement and garden stores, are not toxic to humans but are lethal to pests such as aphids, which prey on garden plants. They are also lethal to bees, which is why the European Union voted to suspend their use in 2012.

Bayer officials disagreed with that decision and maintain that there’s no evidence their products are killing bees.

“There is no scientifically based evidence that individual pesticides are to blame when correctly applied,” Bayer said in a fact sheet on its website.

Over the last three years, Bayer’s chemicals have become popular with lawn care companies and home gardeners. The bees ingest the neo-nicitinoids that are on the plants, and the poisons enter their cells. The bees can’t break them down and become paralyzed, then soon die. That paralysis may be why McDaniel’s guard bees were so listless.

McDaniel has lobbied the state to insist that stores in Maryland not sell these products, or at the very least put a warning label on them.

But Maryland Department of Agriculture bee inspector Jerry Fischer, a longtime beekeeper himself, said that poor management rather than increased pesticide use is the real reason the bees are dying.

Of the more than 1,800 beekeepers in the state, only 32 percent have more than two hives. It’s a hobby, Fischer said, and the mentality is that, if the bees die, the beekeepers can just buy more. He also attributed the problem to weaker queen bees from Georgia.

“There’s no scientific proof that pesticide spraying has contributed to the high die-offs. There’s no proof of it,” Fischer said.

Asked if he agreed with McDaniel about alerting the public, Fischer said: “I don’t think that’s our job. Farming needs these pesticides. Without the farmers and their way of life, what will we do? Import all of our food?”

McDaniel bristles at the suggestion that he and his colleagues don’t know what they’re doing. A beekeeper since 1978, McDaniel has earned the title of Master Beekeper from the Eastern Apicultural Society and has taught dozens of others the basics of beekeeping.

“We didn’t all get stupid at once,” he said.

With no movement from the state or the EPA to ban or label neo-nicitinoids, beekeepers are taking it upon themselves to educate homeowners. McDaniel and his wife travel the region selling their honey and candles at fairs, and they bring a bottle of the pesticides to show homeowners what not to use.

In Norfolk, beekeeper Frank S. Walker has put up fliers around the city with a photo of a swarm. “Just Don’t Do it,” the flier reads, with a slash through a can of insecticides. Walker’s phone number is on the flier, and he or one of his fellow beekeepers will come and take the swarm if someone calls him.

He’s also trying to educate homeowners to plant native flowers, giving the bees a wider variety of food sources.

“In the last 10 years, their population numbers have been in free fall, with potentially devastating consequences for our environment and food systems,” said Walker, a safety officer for the U.S. Navy and coordinator of the state beekeeper’s association’s Master Beekeeper Program. “Saving this insect, to me, is as important as recycling and energy conservation.”

Susan Kegley, a biochemist who is CEO of the Pesticide Research Institute in Berkeley, CA, said attitudes like Fischer’s show how regulators have “bought into the party line of the chemical companies.” Kegley is part of a nationwide coalition of beekeepers and scientists who are trying to persuade regulators to put warning labels on some pesticides and ban neo-nicitinoids, or limit their uses.

The turning point for bees, Kegley said, was in 2000, when the U.S. government approved spraying neo-nicitinoids on corn. With 100 million acres of corn in the country, the bees began their plummet. It became more pronounced with the proliferation of genetically modified corn, where the seed is sprayed with pesticides before it’s planted.

The consequences of a bee collapse are enormous in California, Kegley’s state, where she has testified before the legislature with the hope of restricting these pesticides. The almond industry alone needs 1.6 million colonies of bees to pollinate its crops.

Kegley’s institute has started an integrated pest management tool to help municipalities coexist with insects. So far, four entities have signed up for the subscription service, which Kegley hopes she will soon be able to offer for free.

But the pesticide companies are also a powerful force in California, and Kegley is frustrated that the legislature hasn’t grasped the urgency of the situation.

“They have resources I don’t have,” she said. “I do think progress is being made, but I don’t think it’s happening fast enough to save the beekeepers, or the bees.”

Bill Bundy, president of the Virginia Beekeepers Association, said fungicides are also part of the problem. Bees can’t digest pollen directly, so they convert it into bee “bread,” a mixture of honey, pollen and enzymes. This conversion relies on fermentation, and is similar to the process of turning milk into yogurt through certain probiotic organisms. But the fungicides kill those organisms, and prevent the bees from fermenting and digesting the pollen.

Bundy cautions against blaming all the problems on the pesticides. Management, he said, is a culprit, as is the U.S. farmer’s reliance to monocultures that don’t give bees enough variety in their food. Moving the bees, too, causes stress. And some places are just not bee-friendly.

“I have bees at my home and also at four other farms. Over a period of two or three years, I treat all of them the same, and I find that in a certain location, they just don’t do well,” Bundy said.

McDaniel says he’ll continue educating customers about “neo-nics” while he still has bees to provide products. So far, he said, his bees are faring much better than they did last year. Maybe, he said, homeowners are getting the message.

“If it comes in a blue bottle,” McDaniel said, “It’ll kill bees.”