Exposure to pesticides makes bees less productive and efficient. A new study has identified yet another harmful effect on bumble bees by neonicotinoid compounds, which are the most widely used class of insecticides. Exposure to these compounds is likely contributing to the declining population numbers among pollinator species worldwide.
It has been previously established that neonicotinoids are responsible for a reduction in colony size, but the actual behavior that impairs the colony growth has remained unclear.
To investigate, the researchers monitored the behavior of bumble bees in multiple colonies using a tiny robotic platform. Some of the colonies were exposed to environmentally realistic concentrations of imidacloprid, a common type of neonicotinoid.
The worker bees exposed to the neurotoxic pesticide showed measurable changes in behavior within the nest. They became less likely to feed and care for larvae, less active, and more likely to be found toward the outer edge of the nest.
The experts noted that these behavioral effects varied depending on the time of day, with much less activity at night. Study lead author Dr. James Crall is a postdoctoral fellow at Harvard University.
“Bees actually have a very strong circadian rhythm,” said Dr. Crall. “So what we found was that, during the day, there was no statistically observable effect, but at night, we could see that they were crashing.”
The researchers also found that the impact of pesticide exposure made it more difficult for bees to regulate their body temperature and to build a protective wax cap over the colony.
“Almost all of our control colonies built that cap,” said Dr. Crall. “And it seems to be totally wiped out in the pesticide-exposed colonies, so they lose this capacity to do this functional restructuring of the nest.”
The study is published in the journal Science.
By Chrissy Sexton, Earth.com Staff Writer