A new study published on August 15 in Nature suggests that alternatives to harmful neonicotinoid pesticides may be just as harmful to bumble bees. New sulfoximine-based pesticides were touted as a ‘bee-friendly’ alternative to neonicotinoids, but have now been shown to drastically reduce bee colony numbers (1).
Human activities and climate change over the past century have led to a dramatic decline in bee numbers and the bumblebee has now sadly made it onto the list of endangered species. These natural pollinators play a crucial role in the overall exosystem and 35% of food produced globally depends on bees. Scientists have identified the main culprit as Colony Collapse Disorder (CCD) ― a phenomenon that occurs when the majority of worker bees in a colony disappear and leave behind the queen ― for which there are several possible contributors, including disease, parasites, stress, and most notably, agricultural pesticides.
Pesticides are used to protect crops against insects, such as aphids, by acting on the nervous system of the insects, essentially paralyzing and killing them. Although not lethal to larger species, such as mammals and birds, they can have harmful effects, particularly on bees, affecting their navigation, ability to find food, and reproductive activities, and thus, their ability to form new colonies.
In April, despite opposition from farmers, the European Union voted in favour of banning the agricultural use of five neonicotinoid pesticides, except inside closed greenhouses. On August 15, Canada announced plans to phase out two of the three main neonicotinoid pesticides over a three-year period. Sulfoximine-based insecticides have become popular alternatives. Some of these either already licensed for use or under consideration in several markets across the globe, including the European Union. But the effects of Sulfoximine-based pesticides may be just as detrimental to bees. Last year, the licensing for two sulfoximine-containing products was suspended in France, due to environmental concerns including the potential toxic effects on bees.
To investigate the potentially harmful effects of sulfoximine on bee colonies, Harry Siviter and colleagues at the Royal Holloway University of London fed bumble bees sulfoxaflor-spiked sugar. Sulfoxaflor was the first commercially-available sulfoximine-based pesticide on the market and like neonicotinoid pesticides, works by acting as an insect neurotoxin. The exact dose― an important factor in pesticide studies― was based on data from the U.S. Environmental Protection Agency on pesticide concentrations in the nectar collected by bees from flowers sprayed with the pesticide.
The study showed that Sulfoxaflor has a significant effect on the reproductive activities of bees. Colonies exposed to the chemical were found to produce fewer worker bees than control colonies between two and three weeks after exposure and 54% fewer new queens and males (the bees that reproduce) nine weeks after exposure.
Although pesticides are frequently used to increase crop yields, their overall impact on the ecosystem may, in fact, be negative. The findings of this recent study along with existing and future research should be used to improve our understanding of the risks associated with the use of any type of pesticide and should be taken into consideration in any licensing risk assessments in the European Union. This will be crucial to ensuring a sustainable future and developing strategies, including the potential use of non-chemical alternatives, to minimize the negative effects on bees while supporting farmers struggling to reduce crop damage.
(1) Siviter, H., Brown, M.J.F., and Leadbeater, E. Sulfoxaflor exposure reduces bumblebee reproductive success. Nature (2018). DOI: 10.1038/s41586-018-0430-6