The most widely-used type of pesticides are the neonicotinoids, but they are likely to be banned in many countries because they are bad for bees. Most importantly for conservation, if bumblebees are exposed to them their colonies produce fewer queens. Sulfoximine pesticides are now being used instead of neonicotinoids, but their effects on bees have not yet been tested. To get a licence, manufacturers only have to demonstrate that exposure does not immediately kill workers, so we don’t know what effects they have due to effects on bee behaviour. Since neonicotoinds also passed these tests, it is important to test whether sulfoximines also badly affect bee colonies.
We exposed bumblebee colonies on a university campus to the level of a sulfoximine they are likely to encounter on farms, by feeding colonies sugar solution tainted with low levels of sulfoximine such as they would pick up from sprayed crops. This exposure reduced the number of workers that were produced, with the knock on effect that the colony produced fewer queens by the end of the season: exposed colonies produced no queens at all. This effect happened even though we exposed colonies to pesticide for 2 weeks and then allowed them to forage freely.
The results suggest that sulfoximine pesticides may be no less bad for bees, and so the health of farmland, than the neonicotinoids. It might be safer to only treat crop seeds rather than spraying on the plants, but neonicotoinds sprayed only on seeds affect bees by getting into the nectar. Pesticides should no longer be licensed for use before checking whether they have non-lethal effects on bees, to avoid having a endless cycle of pesticide licensing then removal from sale.