Honeybee populations have been decreasing in recent decades, but insecticides, when administered at normal levels, are not to blame, according to a recent study from university researchers.
The study, which took place over three years, was published in PLOS ONE on March 18 and analyzes the effects of imidacloprid, the most commonly used insecticide, on honeybee colonies’ health, said Galen Dively, the study’s lead author and university professor.
“I figured it would be controversial,” Dively said. “It’s a really hot topic right now.”
Dively said his research team collected data from 40 hives the first year and 32 hives the second year by opening the hives every two weeks to pull all their frames out and extract data on the impacts of the bees’ exposure to the insecticide.
While insecticides are a contributing factor of the declining health of bee hives, the study suggests it is not the dominant cause, Dively said.
David Hawthornecq, another co-author and university professor, said the team’s research shows the complexity of bee hives.
“This may be surprising to those who think that the insecticides are 100 percent safe or 100 percent dangerous,” said Hawthorne, who also is the education director at the National Socio-Environmental Synthesis Center. “Honeybee colonies are complex systems that have the ability to buffer themselves against some environmental threats such as toxins. Our results show that sometimes they can effectively buffer themselves from this insecticide and sometimes they cannot.”
To conduct the study, the research team, which included about 10 undergraduate students, gave various levels of insecticide-laced pollen to honey bee colonies, Dively said. Though the high levels of insecticide negatively affected the bees, that is not what they experience in the real world. The normal levels of exposure did not have as harmful of an effect.
The study was funded by a $500,000 grant from the U.S. Department of Agriculture’s Bee Research Laboratory, Dively said. The study concludes that there is no evidence the realistic exposure of insecticide on honeybees is a significant contributing factor to colony decline.
“You get higher, like at 20 times the average exposure [of insecticide], and then you start to see effects on queen [bee] health and then we lose queens, and we have more breed-less periods and lower winter survival,” he said.
Dennis vanEngelsdorp, a university professor and bee researcher, said while there is debate about the main cause of bee losses, the results of the study were not surprising.
The various stress factors that lead to honeybee losses include parasitic mites, pathogens such as viruses, contact between viruses and mites, malnutrition, pesticide exposure, loss of habitat and stress, he said.
“There are a lot of things contributing to bee health, and we need to be looking more at the data, rather than following instinct,” vanEngelsdorp said.
