There’s no denying that insecticides and honey bees can be a toxic mix. Bees, after all, are insects and insecticides are designed to kill insects. But they can vary greatly in their toxicity to bees, depending on the type and the dosage.
That’s one of the findings of a study being conducted by entomologists at the USDA-Agricultural Research Service’s Jamie Whitten Delta States Research Center and Mississippi State University’s Delta Research and Extension Center, both in Stoneville, Miss.
A group of researchers, including Jeff Gore, Extension/research professor at the DREC, has begun testing 42 commonly-used pesticides in a realistic field setting to determine their toxicity levels for honeybees. The pesticide study examined 40 insecticides, one herbicide and one fungicide.
USDA senior investigator YuCheng Zhu and his colleagues found that 26 pesticides killed nearly all bees that came into direct contact with them. However, seven pesticides – including glyphosate, the active ingredient in Roundup and other weed control products -- killed practically no bees.
“There are many chemicals that have been used in agriculture that were once thought safe for bees,” said Jeff Harris, MSU Extension Service bee specialist and Experiment Station researcher. “This study was important to determine what impact these pesticides have on honeybee health.”
Harris said the study was also important in the way it tested toxicity.
Method of application
“Many times chemicals are tested for acute dermal toxicity, when different doses are touched to the body of the bee. Others look at acute oral toxicity, when the chemical is put in the bees’ food,” he said. “The big question is what happens in the environment, and this study tried to address that question.”
John Adamczyk, entomologist and research leader with the USDA-ARS lab in Poplarville, Miss., said the study looked at acute toxicity, or whether these pesticides killed bees when they were exposed to realistic doses of the chemicals in an agricultural setting.
“This study gives us a baseline,” Adamczyk said. “We were looking at the acute kill, and we were able to put these chemicals in a sort of order based on toxicity.”
Adamczyk said the study produced no surprises. The chemicals tested were found to have toxicity similar to what the manufacturers and the Environmental Protection Agency determined from the extensive analyses of the products prior to registration.
“This information will help beekeepers and growers understand that there are certain pesticides that are clearly very toxic to bees, and it will help them manage that risk,” he said. “Chemicals are often used in combination with other chemicals, and with this data, we can quickly look at what effect these combined chemicals will have on pollinators.”
The study applied chemicals as spray to mimic application methods used by farmers. They tested those commonly used in agricultural settings and simulated a situation where an adult bee in a cotton field is accidentally sprayed.
Researchers found that many but not all of the neonicotinoids, organophosphates and pyrethroids tested killed nearly all of the bees these chemicals touched. However, a few pesticides, including glyphosate and acetamiprid, killed practically no bees in the test.
A few chemicals were found to be more toxic than originally assumed when used at field application concentrations. One pesticide that was considered a high risk for bees was found to be only an intermediate risk when used at the labeled rate.
Adamczyk said this study that created baseline data was just the tip of the iceberg, and much more work needs to be done.
“The impact will come in understanding the toxicity of certain combinations and understanding the residual effect chemicals have on bees,” he said. “If farmers can understand that they need to be extra careful with a particular mixture, they may try something different that is less toxic to bees but still effective for their purposes or be mindful about when and how they spray.”
For more on the pollinator health issue, visit http://www.epa.gov/pollinator-protection/federal-pollinator-health-task-force-epas-role