We need bees to pollinate the plants that feed us. And bees need us to stop inadvertently poisoning them with the insecticides we use to keep those plants healthy. Unfortunately, just as we start to make progress on reducing the worldwide use of neonicotinoids (a class of insecticides that are toxic to bees), it seems like we might be at risk of rolling out an alternative insecticide that causes similar problems.

“Sulfoximine-based insecticides are the most likely successor [to neonicotinoids]” write the University of London’s Harry Siviter and his colleagues in a paper published in Nature this week. And that’s not great, as they found that bumblebee colonies exposed to a sulfoximine-based insecticide called sulfoxaflor suffered severe effects compared to a control colony. The insecticide didn’t kill the bees, but it damaged their ability to run a successful colony—a similar effect to neonicotinoids.

Contamination

When insecticides are sprayed on crops, they settle not just on the crops themselves but also nearby wildflowers. Crops grown from insecticide-treated seeds also result in contaminated dust, soil, and pollen. This all exposes foraging bumblebees to the insecticide and also means that contaminated pollen and nectar make their way back to the bee colony, where larvae are exposed.

Siviter and his colleagues wanted to understand what would happen to bee colonies that had been exposed. So, they started 52 colonies with wild bumblebee queens, and exposed half of the colonies to sulfoxaflor-laced sugar water. They kept the amount of sulfoxaflor in the water at a conservative level, meaning that the effects they observed are likely to be a low estimate of what’s possible in an uncontrolled setting.

After the two weeks of controlled exposure, the colonies were moved outdoors and observed. Very quickly, it became obvious that the sulfoxaflor-exposed colonies were not thriving: they produced fewer offspring. In addition, not one of the 36 queen bees produced by the 52 colonies came from the sulfoxaflor-exposed group—they all came the control colonies. (Only three colonies produced all 36 queens, though, so that result should be treated with caution.)

Neonicotinoids have similar effects, but there is a difference in the results. While neonicotinoids seem to hamper bees’ ability to forage, indirectly affecting the health of the colony, the study on sulfoxaflor didn’t seem to show the same problem with foraging. This suggests that the reproductive issues might have a different cause. A better understanding of the concentrations of sulfoxaflor that bees are likely to be exposed to in real-world settings could help to nail down how exactly the insecticide is causing the damage.

Understanding risk

It’s a “valuable first step toward understanding the effects of sulfoxaflor exposure on bees,” writes conservationist Nigel Raine in a commentary on the paper. But other classes of insecticide should be brought into the conversation, too, he adds: “It is vital to ascertain which of these insecticide classes represents the lowest potential risk to pollinators.” And this new paper looks at just one species, when there are more than 20,000 living bee species.

While there’s more work to be done, the results suggest that extreme caution will be needed to avoid finding ourselves in a similar situation to the one we faced with neonicotinoids. Some progress has been made on reducing neonicotinoid use across the globe, although the battle’s far from won. But now, we risk of undoing that progress.

“Sulfoximine-based pesticides are a newly emerging class of product but are already licensed in many countries worldwide, including China, Canada, and Australia,” write Siviter and his colleagues. “Within the European Union... approval has been granted for use in five member states, and applications from seven more member states are currently in progress.” An evidence-based approach is desperately needed, they argue: it’s crucial not just to check that new insecticides don’t kill bees outright but also to understand the long-term consequences for the health of the colonies that keep our food supplies pollinated.

Nature, 2018. DOI: 10.1038/s41586-018-0430-6 (About DOIs).