AURORA, Ore. — An Oregon State University bee expert said that it is wrong to blame colony collapse disorder on neonicotinoid insecticides.
Ramesh Sagili, an assistant professor in the Department of Horticulture at OSU, said that exposure to neonicotinoids and other pesticides is just one of many factors contributing to the recent decline in bee populations.
“We don’t have much evidence at this time that neonicotinoids are causing these losses,” he said.
Sagili characterized colony collapse disorder as “complex and multifactorial.”
“They are like a perfect storm (of factors),” he said Oct. 17 during a pesticide workshop at the North Willamette Research and Extension Center.
Since 2007, bee colony loss on a national scale has been occurring at a rate of about 30 percent a year, twice what is considered normal.
Sagili identified a parasite, the varroa mite, as the No. 1 factor causing this disorder. First found in the U.S. in the mid-1980s, the mite sucks blood from adults and pupae and vectors a disease-causing virus.
Pacific Northwest honey bee losses before the varroa mite emerged were estimated at between 10 and 15 percent, he said. Since the 1990s, when the varroa mite came onto the scene, commercial colony losses have averaged about 25 percent.
Sagili said that in addition to losses caused directly by the mite, pesticides used to control it are contributing to colony collapse, in part by combining with pesticides bees are exposed to unintentionally to create a cocktail of toxicity.
Other leading factors contributing to colony collapse disorder include: migration, where beekeepers move hives long distances, in some cases forcing bees to adjust to extreme temperature changes; mono-cropping, where bees pollinate a single crop, restricting their diet; and malnutrition.
“We think malnutrition is also playing a role,” Sagili said.
Neonicotinoids, first registered for use in the U.S. in 1992, are likely contributing to the disorder, he said, but are not the leading cause.
He said several other insecticides are likely contributing to the decline in the bee population.
Bees are exposed to neonicotinoids by a variety of methods, Sagili said, including feeding on pollen of plants treated with the systemic pesticide, and direct contact with foliar sprays.
Growers can help limit bee losses to pesticides by choosing insecticides with low toxicity to bees, avoiding spraying plants during bloom, and protecting water sources from pesticide contamination, Sagili said.