‘Safe’ Levels of Pesticide Still Hamper Bees’ Memory and Ability to Learn

The honeybee’s foraging routine is deceptively complex. To track down food and ensure the survival of the colony, worker bees must draw on their knowledge of smells, patterns and efficient routes to and from the hive—a process that requires the insects to remember an encyclopedic amount of information.

Bees are currently experiencing an unprecedented decline in population, and according to a new study conducted by researchers from Royal Holloway University of London, their troubles are far from over. The team’s findings, published yesterday in the Journal of Applied Ecology, suggest that the widespread use of pesticides is hindering bees’ capacity for learning and memorization.

Popular Science’s Kat Eschner reports that the scientists analyzed data from more than 100 experiments detailed in 23 lab studies of bees’ responses to floral scents. Typically, when a bee detects the enticing aroma of flower nectar, it begins to stick out its tongue in anticipation. (As Nature’s Heidi Ledford notes, bees’ tongues look like mops but function like straws, allowing the insects to reach deep into flowering plants and retrieve their nectar.) Scientists can even train bees to stick out their tongues after smelling new scents associated with a nectar or sugar reward, meaning the bees learn that a new smell will provide them with food. After exposure to pesticides, however, bees’ foraging skills were impeded. They weren't as good at learning about new smells and weren't sure when, or if, to stick out their tongues.

“Our results show that, when combining data collected from a wide range of studies, insecticides have a significant negative impact on bee learning and memory,” lead author Harry Siviter, a PhD student at Royal Holloway, said in a statement. “This occurs even at the low levels of pesticides that bees would routinely encounter in the field.”

According to Eschner, pesticides’ damaging effects were apparent regardless of whether bees were exposed to high amounts over a short period of time or low amounts over a prolonged period of time. The type of pesticide introduced also had a negligible impact on results.

Pesticides are commonly found in bees’ honey and pollen stores—a 2017 global analysis recorded the presence of neonicotinoids, a class of insecticides once praised for their supposed low toxicity, in 75 percent of all honey samples. These figures suggest that bee larvae, which are potentially more susceptible than adult bees, are exposed to pesticides’ harmful effects as they develop. Although the relative impact of pesticides on larvae versus adults remains relatively unexplored, the paper’s authors note that at least one study suggests exposed larvae take longer to develop, while exposed adults don't live as long.

The results of the large-scale study have a bevy of implications for pesticide regulation. Current guidelines discourage farmers from using enough pesticide to actively kill bees, but as Siviter tells Eschner, the toxins’ “sub-lethal effects,” including damage to cognition and memory, still pose a threat to bee colonies’ long-term survival.

By the end of 2018, a blanket ban on neonicotinoids is set to take effect across the European Union. The ban, approved by member nations in April, follows the publication of a report identifying pesticides’ harmful effects on honeybees and wild bees. As the Guardian’s Damian Carrington notes, proponents of the ban cite bees’ contributions to biodiversity, food production and overall environmental health, while opponents—largely consisting of pesticide manufacturers and farming groups—argue that restrictions will curtail the growth of European agriculture.

It remains to be seen if other global powers, including the United States, will follow in the EU’s footsteps.

Meilan Solly | | READ MORE

Meilan Solly is Smithsonian magazine's senior associate digital editor, history.