Two common insecticides could do a great deal of damage to crucial honey bee populations during the winter.
The researchers found the chemicals neonicotinoid and clothianidin could lead to colony collapse disorder (CCD), which causes bees to abandon their hives in the winter and die of exposure, a Harvard School of Public Health news release reported.
The disorder was believed to be in part brought on by a reduced resistance to mites and parasites as a result of insecticide exposure. This new study found the same level of pathogen infestation in both hives that had and had not been exposed to the insecticides.
"We demonstrated again in this study that neonicotinoids are highly likely to be responsible for triggering CCD in honey bee hives that were healthy prior to the arrival of winter," lead author Chensheng (Alex) Lu, associate professor of environmental exposure biology at HSPH, said in the news release.
A large number of bees have succumbed to CCD since 2006; this is concerning because bees are the "prime pollinator" of about one-third of the world's crops.
To make their findings the researchers looked at 18 colonies that were split into three groups: "one treated with imidacloprid, one with clothianidin, and one untreated," the news release reported. The hives were located in central Massachusetts.
The researchers noticed a significant population decline in all three groups at the beginning of the winter. In January the bee populations in the untreated colony started to increase, but the neonicotinoid-treated group continued to disappear.
By April six of the 12 neonicotinoid-treated colonies had abandoned their hives and perished; only one of the untreated colonies was lost.
"Although we have demonstrated the validity of the association between neonicotinoids and CCD in this study, future research could help elucidate the biological mechanism that is responsible for linking sub-lethal neonicotinoid exposures to CCD," Lu said. "Hopefully we can reverse the continuing trend of honey bee loss."