American bees have been dropping like flies lately, which is bad news for the crops they pollinate and ecosystems they support. It's a complex crisis with a wide range of suspects, but research suggests pesticides are at least part of the problem — namely a class of insecticides known as neonicotinoids.

With that in mind, three U.S. judges decided this week to overrule the EPA and remove a particular bee-killing pesticide from the market. The Ninth Circuit Court of Appeals ruled in favor of several beekeeping and environmental groups, who sued the EPA last year to challenge its 2013 approval of sulfoxaflor.

"Bees are essential to pollinate important crops and in recent years have been dying at alarming rates," Judge Mary M. Schroeder wrote in an opinion. "Because the EPA's decision to unconditionally register sulfoxaflor was based on flawed and limited data, we conclude that the unconditional approval was not supported by substantial evidence. We therefore vacate the EPA's registration of sulfoxaflor and remand."

Made by Dow AgroSciences, sulfoxaflor is designed to kill aphids and other pests on a variety of crops including canola, citrus, cotton, strawberries, soybeans and wheat. But as the EPA itself has acknowledged, the insecticide is also "acutely toxic to bees."

Why would the EPA approve a bee-killing pesticide? "In brief, the key is to limit exposure," the agency explained last year. "The EPA does not allow sulfoxaflor application to plants that are attractive to bees for three days before bloom, during bloom, or until petal fall for the majority of crops. For the remaining bee-attractive crops, we also added advisory language to the labels to notify known beekeepers of scheduled application and to apply these products in early morning or late evening."

honeybee with pollenHoneybee pollination accounts for $15 billion in increased crop value per year, according to the USDA. (Photo: Shutterstock)

Yet the recent decline of U.S. bees — including domesticated honeybees as well as wild, native species — warrants more safeguards than that, according to the beekeepers and environmentalists who sued the EPA. Commercial beekeepers across the U.S. reported losses of 42.1 percent from April 2014 to April 2015, the second-highest annual decline in a decade-long trend known as colony collapse disorder.

The EPA had reportedly asked Dow for additional studies about how sulfoxaflor affects various species, including bees, but ended up approving the pesticide in May 2013 even though Dow hadn't completed additional studies the agency requested.

In this week's ruling, the court ordered EPA officials to obtain more information about the impact of sulfoxaflor on bees, as dictated by federal environmental regulations. Any future approval of the pesticide will depend on those data.

Protecting bee populations isn't just an ecological issue. While native bees are crucial to ecosystems across the U.S., commercially managed honeybees also play a vital role in perpetuating the food supply. According to the U.S. Department of Agriculture, they pollinate plants that provide a quarter of the food eaten by Americans, accounting for more than $15 billion in increased crop value per year.

honeybeesHoneybees ply their trade at the J & P Apiary in Homestead, Florida. (Photo: Joe Raedle/Getty Images)

"Our country is facing widespread bee colony collapse, and scientists are pointing to pesticides like sulfoxaflor as the cause," says Greg Loarie, lead counsel in the case for Earthjustice, in a statement. "The Court's decision to overturn approval of this bee-killing pesticide is incredible news for bees, beekeepers and all of us who enjoy the healthy fruits, nuts, and vegetables that rely on bees for pollination."

Dow AgroSciences issued its own statement to say it "respectfully disagrees" with the court's decision, and "will work with EPA to implement the order and to promptly complete additional regulatory work to support the registration of the products." The company is also considering its options to challenge the ruling, it adds.

For now, however, the judges say the risk crops face from pests like aphids pales in comparison to the overall risk posed by a loss of bees. "[G]iven the precariousness of bee populations," the court writes, "leaving the EPA's registration of sulfoxaflor in place risked more potential environmental harm than vacating it."

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.