Swiss agrochemical giant Syngenta has petitioned the US environmental Protection Agency (EPA) to increase the legal tolerance for residues of several crop protection agents, including a controversial neonicotinoid (neonic) pesticide, in several crops.

The petition is particularly controversial as neonics have been suspected of at least contributing to the phenomenon bee colony collapse disorder and is currently subject to a temporary ban in Europe.

The US has lost more than half its managed honeybee colonies in the last 10 years, according to the Pollinator Partnership, a nonprofit organization dedicated to the protection of pollinators and their ecosystems.

Syngenta's request, published in the Federal Register, applies to use of thiamethoxam in alfalfa, barley, corn and wheat - sprayed on both the crop and the post-cultivation stover. The Swiss producer is seeking to increase the levels from as low as 1.5 times for stover from sweet corn to as much as 400 times for hay from wheat.

Increases in neonic use are especially concerning in forage crops such as alfalfa, as bees collect pollen from the blooms, said Aimee Simpson, policy director and staff attorney for the advocacy group Beyond Pesticides.

Syngenta said it is seeking to change the tolerance levels in order to use thiamethoxam as a leaf spray, rather than just a seed treatment, on late- to mid-season insect pests.

The increased residues could become a problem if farmers are spraying thiamethoxam at a time when alfalfa is blooming, Reed Johnson, a bee toxicologist and an associate professor of entomology at Ohio State University, told US news media. But he added that most commercial growers cut the crop before the flowering stage.