Fertilizers and pesticides could limit pollination by changing how bees sense flowers

Bees are more likely to avoid flowers sprayed with fertilizers and pesticides because of the way these chemicals alter a plant’s natural electric field, according to a new study (PNAS Nexus 2022, DOI: 10.1093/pnasnexus/pgac230). Although bees typically rely on sight and smell to find nectar and pollen, they also depend on electrical signals generated by ions moving through the plant cells. Bees use them to determine which flowers are worth landing on.

But agricultural compounds can induce a stress response in the plant, which can temporarily alter these invisible electrical cues, says Ellard Hunting, a sensory biophysicist at the University of Bristol, who led the study. Hunting and his team found that a commercially available liquid fertilizer and the pesticide imidacloprid can increase the electric potential of flowers for up to 25 min. “That’s substantially longer” than natural phenomena such as wind that can also cause these signals to fluctuate, Hunting says.

To confirm that the chemicals don’t alter other cues that the bees rely on, such as color or odor, the team artificially manipulated the electric fields of flowers by applying a voltage using electrodes. The bees approached the electrically manipulated flowers but didn’t pollinate them nearly as often as unmanipulated ones. It’s as if applying an electric field makes the flower so blindingly bright the bees no longer see it, Hunting says.

“The way forward would be to look for things that don’t stress out the plant,” he adds, or to apply these chemicals only to soil, which could minimize the effect.