There's a mounting pile of evidence that three particular neonicotinoid insecticides, clothianidin, imidacloprid and thiamethoxam, are harming bees. During the late 1990’s this class of pesticides began being used to treat corn and other field crop seeds. Today, they are the most commonly used pesticides in the U.S., and have covered millions of acres.

Despite their omnipresence, their safety for pollinators is increasingly in question. And the proof keeps pouring in.

"It's reached a point when it's time for the Environmental Protection Agency to withdraw the registration of these pesticides until proven safe," says Scott Black executive director of the Xerces Society for Invertebrate Conservation. "If things were done right, this information would have gotten to scientists and the EPA before [the pesticides] got to the market," continues Black. "But, now we have enough data to conclude that there may be a substantial risk from these insecticides."

Last month, the European Safety Authority (EFSA) announced that clothianidin, imidacloprid and thiamethoxam put bees at a " high acute risk," particularly through their contact with pollen, nectar and seed dust. The study is part of the impetus behind the EU's upcoming March 15th vote on whether to ban the use of these pesticides on corn, oil seed rape, sunflowers and some other crops. The ban would be for two years.

It's a ban that fell on the deaf ears in the U.S. last year. But, that was before more research. In March 2012, a study published in Science showed that neonicotinoid pesticide use hinders the growth of bumble bee colonies and reduces the number of new queens by 85%. Bad news for bumble bees.

"In honey bee colonies the large worker force gives the colony a buffer and while we have shown effects of neonics on individual bees, at the colony level we normally have not seen them," wrote Jeff Pettis, an entomologist and researcher with the USDA, in an email. "The bumblebee studies do show a clear effect at the colony level."

Another report shows that when bees are exposed to thiamethoxam at non-lethal levels, their homing system fails. Then there are people who believe we've only touched the tip of the honeycomb when it comes to the harmful effects of pesticides. One of these is Rusty Burlew, a beekeeper and bee enthusiast, who runs a website called honeybeesuite.

"Both field and laboratory testing on pesticides is done on adult bees and very little, if any, is done on the larval stages because it has not been required for registration," wrote Burlew via email. "These chemicals, and others, are adversely affecting bees in the larval stage of development."

Burlew adds that pesticide testing is done on a product-by-product basis, even though they are not used that way. Most pesticides are used in combination with others and synergistic effects are common. Not only that, but as the pesticides degrade they often produce metabolites that are more toxic to an organism than the original formulation. Like Black, Burlew believes these pesticides should be embargoed until proven safe.

"These pesticides should be banned until they are studied on all stages of bee development (especially the larval stage which is the most vulnerable), until the toxicity of pesticides used in combination with others is studied, and until all the pesticide metabolites are studied as well," wrote Burlew. Only then can we make an informed decision."

The question remains: what does the EPA think since it regulates the use of these chemicals? The EPA granted a conditional, or temporary, registration to clothianidin in 2003. The same approval was given to thiamethoxam. Imidacloprid was registered in 1994. It was not conditional. The EPA is now re-evaluating the safety of neonicotinoids. According to Scott Black, the EPA has stated that the registration review process will take several years. At the earliest , the new verdict for imidacloprid will be in 2016 and 2017 for clothianidin and thiamethoxam.

There's one large caveat should the EPA rethink the registration of these neonicotionids: the replacement compounds need to be better, not worse.