US environmental regulators are under fire from beekeepers and conservationists who say they are failing to vet risky pesticides that put people and valuable crop pollinators like bees in peril.

On Wednesday, the Natural Resources Defense Council issued a scathing report of the Environmental Protection Agency's record of using a loophole to allow more than 10,000 "untested or under-tested" pesticides on the market.

That followed a lawsuit brought last week by several beekeepers and environmental groups, accusing the EPA of failing to protect pollinators and challenging practices that speed to market about two-thirds of all pesticides.

The suit seeks to suspend the EPA registrations of pesticides that have been identified as toxic to bees.

Pesticides in a family called neonicotinoids are believed to contribute to colony collapse disorder, a mysterious plague that has killed off about 30 percent of bees annually since 2007.

The two pesticides highlighted in the federal district court suit are clothianidin and thiamethoxam, both of which were first used heavily in the mid-2000s, around the time that the bee die-offs began worldwide.

Last year, France banned thiamethoxam, found in a pesticide made by Swiss giant Syngenta, after research showed it shortened bees' lifespans.

A handful of European countries have restricted or banned neonicotinoids but the European Union earlier this month failed to reach a consensus on the issue.

In the case of clothianidin, Bayer CropScience was granted conditional registration from the US EPA in 2003.

It has been used widely to treat canola and corn seed. Nearly all of the 92 million acres of corn seeds planted annually in the United States are coated with these pesticides, said Larissa Walker of the Center for Food Safety, one of the parties bringing the lawsuit.

"A lot of the farmers feel that it is difficult for them to find seeds these days that don't contain a neonicotinoid product," she told AFP.

The EPA approved the pesticide but said Bayer had to submit a field study of the effects on bees by 2004.

"Unfortunately the field study that Bayer handed in was not only late by several years but was poorly conducted, and had some serious flaws in it," said a senior scientist at NRDC, Jennifer Sass.

A separate study by Purdue University in 2012 showed clothianidin-coated seeds contaminated farm machinery with as much as 700,000 times a bee's lethal dose of pesticide.

"Nonetheless, EPA continues to rely on the Bayer CropScience studies only that failed to find harmful effects on bees," Sass told reporters.

In response, Bayer CropScience said it "has no concerns about the quality of the field study in question" and that the NRDC claims "are incorrect and unwarranted with regard to bee health," according to a statement sent to AFP.

Environmental groups say a congressional loophole dating back to 1978 has allowed the EPA to approve more than 10,000 pesticides with minimal testing.

This "conditional registration" was meant for rare cases -- such as a disease outbreak or a public health crisis -- but instead has been used for 65 percent of the 16,000 pesticides on the market, the NRDC said.

Mae Wu, an attorney at NRDC, said the EPA was not tracking the conditional registrations properly and that supposedly temporary pesticides were falling into a "black hole."

The EPA said it "does not comment on pending litigation."

However, it defended the practice of conditional registration, saying 90 percent of the pesticides approved that way are identical to or differ just slightly from products already on the market.

The EPA also said it is "accelerating the schedule for registration review of the neonicotinoid pesticides because of uncertainties about these pesticides and their potential effects on bees."

The NRDC urged the EPA to review all its conditionally registered pesticides, cancel the registration for clothianidin and a germ-killer known as nanosilver, and start a publicly searchable database of approved pesticides.