Trinity College Dublin

By Shannon Kelleher

Pesticides sprayed on farmland continue to harm bumblebees in Europe, underscoring a need for more protective regulatory oversight, according to a new study that revealed how bees respond to real-world pesticide exposure at 106 sites across eight countries.

The analysis, part of a project called PoshBee that aims to monitor and improve bee health across Europe, went beyond standard field experiments that measure how bees respond to a single substance in a test environment. Instead, the researchers studied bumblebees in actual farm landscapes – apple and rapeseed fields – treated with multiples pesticides. Bumblebee colonies with greater toxicity from pesticides in their pollen had fewer total cocoons, weighed less altogether, and had fewer new queens, according to the study, which was published Wednesday in the journal Nature. Insecticides, including neonicotinoids, pyrethroids, and organophosphates, posed a greater risk to the bees than other types of pesticides.

“This is a very important study,” said Margaret Reeves, a senior scientist at the Pesticide Action Network (PAN) North America who was not involved in the study. “Pesticides are almost never used in isolation [and] can drift long distances, with those used in close proximity to one another especially likely to interact. Much of this we simply don’t understand because various kinds of mixtures are seldom studied.”

“If pesticides in agricultural fields pose the problems described to bees, just imagine what these pesticides are doing to the millions of field workers in those same fields,” she added.

The findings point to a need to monitor approved pesticides after farmers begin spraying them in the environment, a strategy that could also safeguard species important for pest control and soil quality on farms, said Jessica Knapp, an assistant professor of botany at Trinity College Dublin in Ireland and an author of the study.

“For us, it’s not necessarily that [risk assessment] should become tighter, it’s that it should become more realistic with what these species are actually exposed to in real landscapes,” she said. “Once [pesticides] go through all the regulation, the testing kind of stops, which is obviously nonsensical because we don’t know what is happening in these real environments. That’s where we really want a change.”

The study comes on the heels of the European Parliament’s failure last week to pass the Sustainable Use of Plant Protection Products Regulation (SUR), proposed legislation that included targets to slash the use and risk of chemical pesticides in the European Union in half by 2030. SUR was rejected because decision makers felt that pesticide reduction wouldn’t be economically viable for farmers, said Knapp, adding that farmers need such protections to ensure healthy landscapes for future generations.

“Countries outside the [European Union] should also take note of these results, as many nations have looser pesticide regulations that may lead to more magnified impacts on wild bees,” said Clara Stuligross, a postdoctoral researcher at the University of California, Riverside who was not involved in the study.

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