Bee Deaths And Seed Treatments

Particles of insecticides used as seed treatments may deliver a fatal blow to honeybees in cornfields, researchers have found. The scientists say exposure of bees to the insecticides, known as neonicotinoids, may cause honeybee colony losses. But pesticide manufacturers contend that, under normal conditions, the treated seeds don’t pose a serious risk.

Seed coatings containing insecticides are popular with growers because only small amounts are required to protect young plants from pests. The neonicotinoids work by disrupting the nicotinic acetylcholine receptor of an insect’s nerve cells.

But starting in the late 1990s, beekeepers in Europe raised alarms about two neonicotinoids, clothianidin and imidacloprid, claiming they were to blame for sharp declines in honeybee colonies, now known as colony collapse disorder. As researcher Andrea Tapparo and colleagues at Italy’s University of Padua point out, in Europe, corn sowing from mid-March to May is often followed by a rapid disappearance of bees.

Earlier research showed that after treated corn is planted, the amount of pesticide residue in the soil is below 50 ppb, which is not high enough to cause acute toxicity in bees. Tapparo’s team looked instead at the amount of insecticide that falls to the ground and is released to the air during seed planting. Farmers use pneumatic machines that suck seeds out of a bin and blow them toward the ground. In the process, bits of the seed coating break off and can become airborne.

The team reports that measurements of air particulates and residue on dead bees at the time of planting indicated the bees’ levels of exposure to neonicotinoids were high and could explain colony losses (Environ. Sci. Technol., DOI: 10.1021/es2035152).

Seed treatments with neonicotinoids are manufactured by Bayer CropScience, BASF, and Monsanto. Utz Klages, head of external communications for Bayer CropScience, contends the study does not show the treated seeds cause colony collapse disorder. “The work of this research team demonstrates that lethal exposure of honeybees to abraded seed dust is only likely to occur under very specific and unusual conditions and provides a basis for further targeted efforts to limit the possibility of such occurrences,” he says. For example, the exposure may be reduced by improving the seed coatings and modifying the planting machines.