In a test of 42 commonly used pesticides conducted by USDA Agricultural Research Service and Mississippi State University scientists, glyphosate and acetamiprid were found to have only a limited effect on honeybees.
Researchers tested the pesticides in a realistic field setting to determine their toxicity levels. Twenty-six pesticides, including several neonicotinoids, organophosphates, and pyrethroids, killed nearly all of the bees that came into contact with them.
Seven pesticides, including glyphosate and acetamiprid, killed practically no bees in the tests.
The insecticide sulfoxaflor was found to be near the middle in terms of toxicity, an important finding as EPA's approval of the pesticide was recently overturned by the U.S. Ninth Circuit Court of Appeals.
According to the testing, sulfoxaflor was found to be less toxic to bees than permethrin, a pyrethroid insecticide that is used in agriculture, household pesticide products, flea shampoos for pets, and in head lice products for people.
Also, four pesticides that had been considered moderately toxic to bees – methoxyfenozide+spinetoram, carbaryl, indoxacarb, and 1-cyhalothrin+chlorantraniliprole – were found to be higher risk when field-application concentrations were considered.
One pesticide, gamma-cyhalothrin, which was considered to be a high-risk chemical, was found to be only an intermediate risk when used at the labeled rate.
How the study was conducted
Using a modified spray tower to simulate field spray conditions, the researchers mimicked a situation where an adult bee in a cotton field accidentally gets sprayed.
The Entomological Society of America notes that this is an important distinction from previous studies that tested the active ingredients only, or that used artificial feeders with the pesticides in a sugar solution.
According to ESA, none of those methods provide appropriate measures of the amounts of pesticide exposure in the field.
ESA says field spraying of insecticides and other pesticides may effectively kill insects, but the risk to bees can be reduced with pesticides of lower toxicity.
The study determined that a number of pesticides, including a neonicotinoid, showed little to no toxicity to bees, meaning they could be effective alternatives to organophosphates, carbamates, and other neonicotinoids, ESA said.
Researchers said the data, particularly the ratios of field application rates to lethal concentrations of each pesticide, "provide a quantifying scale to help extension specialists and farmers with pesticide selection to maintain effective control of target pests and minimize the risk to foraging honey bees as well."
The results were published in the Journal of Economic Entomology.