The humble bumblebee just can’t catch a break. Numbers have been on the decline in recent years, with at least one species facing extinction. Pesticides have been blamed for declining colony sizes – and a new study appears to offer answers as to why (1).
James Crall and a team at Harvard University used environmentally relevant concentrations (~6 ppb) of imidacloprid (a neonicotinoid pesticide) in artificial nectar to assess its impact on bumblebee colonies versus control colonies. By supergluing “BEEtags” (QR codes) onto the backs (specifically, the mesoscutum) of all bumblebees in all colonies, the team was able to use IR-sensitive cameras to track within-nest behavior.
The experimental design was fascinating, with many moving parts (including the bumblebees of 18 commercial colonies): camera gantries with Smoothieboard motion controllers, IR-LED arrays, and a Matlab computational pipeline. But despite the complexity of the core experiment, the authors did not skimp on analytical chemistry. The mean concentration of imidacloprid in dosed nectar was confirmed by LC-MS to be 5.34 ppb (+/- 0.29 SE). The authors also assessed whole-body imidacloprid concentrations after the experimental period from dosed and controlled colonies. Pesticide analysis will be familiar to a select group of readers – but have any of you needed to use the words bumblebee and bead beater in the same sentence?
The group discovered that imidacloprid had a “profound” effect on worker bees’ social behavior – particularly at night: those exposed to the neonicotinoid spent less time taking care of the nest and nursing larvae, remaining on the periphery of the nest. It also impaired bees’ ability to warm the nest and build insulating wax caps, affecting thermoregulation of the entire colony.
“This work […] opens up a new set of questions, not just about what the direct effects of pesticides are, but how those pesticides impair the ability of colonies to cope with other stressors,” said Crall. “It changes both how we go about practically testing agro-chemicals in general, but it points to specific questions about whether we might see stronger declines in certain environments […] we should be very, very concerned about how the ways in which we’re changing the environment is undercutting and decimating insect populations.”
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References
- J Crall et al., “Neonicotinoid exposure disrupts nest behavior, social networks, and thermoregulation”, Science, 362, 683–686 (2018). DOI: 10.1126/science.aat1598