We know that neonicotinoid insecticides are no-good for bees and other pollinators, even at very low levels of exposure. We know the major neonic — imidacloprid (Admire®) — is the single most acutely toxic pesticide to bees ever discovered, narrowly edging out the former #1 methyl parathion.
But scientists are still trying to figure just how and why neonics seem to trigger honeybee and wild pollinator colony collapse at exposure levels well below those sufficient to kill bees outright.
In a new study published in the journal Science last month, a team led by researchers from Harvard used high-tech methods to measure the impact of the imidacloprid on bumblebee behavior.
The behavior of the bees in this experimental model was monitored by a robot-guided camera system that was mounted over the top of colonies of bumblebees. There were 18 colonies in all, and each had access to a foraging chamber stocked with nectar. Half of the colonies were fed nectar containing amounts of imidacloprid equivalent to real-world environmental exposure near fields treated with the insecticide. The other half (the control group) was fed pesticide-free nectar.
The robotic camera was able to monitor up to 12 colonies at a time. Plus, individual bees were tagged with simple QR codes so that the camera could track behavior bee by bee (see image at top right, Photo: James Crall via Mongabay).
This means that researchers now have “an automated, robotic platform for continuous, multicolony monitoring of uniquely identified workers” (Crall et al., 2018). Apparently entomologists get a really great new toy under the Christmas tree this year!
One thing that set the study apart from previous research — the team used special light-blocking fabric that allowed UV light in for filming but simulated night-time conditions in the colony.
“A lot happens at night in bee nests, including nursing and caring for young,” writes Stephanie Parker in an article about the research posted at Mongabay.com. But, “nighttime is often under-studied when it comes to looking at the impacts of these chemicals on bumblebee populations” (Parker, 2018).
The camera-system worked well and researchers observed some distinct behavior changes in the imidacloprid-exposed bees when compared with the control group. In particular, the insecticide impaired the ability of exposed colonies to thermoregulate, which is key as temperatures rise and fall in the crowded quarters.
The difficulty regulating temperature affected the developing young and larvae the most. In every colony that was exposed to the neonics, worker bees did not build an important wax coating over the developing eggs, larvae and pupae – normal bee behavior during cold snaps. “That behavior was completely wiped out in pesticide-exposed colonies,” said lead author James Crall in Parker’s article. Control colonies responded to cold temps by building the wax covers, i.e. normal bee behavior.
Other unusual behavior was observed in the neonic-exposed bees, including a tendency to linger at the edges of their nest and spend “less time nursing, taking care of the nest, and interacting with nest-mates.” In fact, exposed bees “were less active overall than bees that had access to uncontaminated nectar” (Parker, 2018).
Given the complex nature of social interactions in a bee colony, and the critical role it plays in the division of tasks that allows a colony to survive, these kind of behavioral impacts are worrisome. Given that neonicotinoids have also been shown to impact foraging and reduce bees ability to fend off viruses and infections, these new findings add to the reasons that farmers and regulators need to find more effective ways to protect pollinators that both farmers and consumers depend on.
NOTE: For more on the impacts of neonics on pollinators, see the Xerces Society for Invertebrate Conservation report “How Neonicotinoids Kill Bees.” The full report and the executive summary are both available online. They also have developed a database of research articles on pesticide impacts on pollinators, available here for those who want the deep dive.
Crall, James D., Switzer, Callin M., Oppenheimer, Robert L., Ford Versypt, Ashlee N., Dey, Biswadip, Brown, Andrea, Eyster, Mackay, Guérin, Claire, Pierce, Naomi E., Combes, Stacey A., & de Bivort, Benjamin L., “Neonicotinoid exposure disrupts bumblebee nest behavior, social networks, and thermoregulation,” Science, 2018, 362:6415, 683, DOI: http://science.sciencemag.org/content/362/6415/683.abstract.
Stephanie Parker, “Camera-wielding robot records effects of pesticide on bees’ behavior,” Mongabay, Published online: 11/21/2018, Date accessed: 12/5/2018.