Bumblebee Pesticide: "Bee Depressant" Chemical Makes Hive Life Antisocial

If you know where to look, you can witness the decline of a bee society 

As Albus Dumbledore famously told Voldemort in one epic Harry Potter duel, some fates are worse than death. It’s just as true in the wizarding world as it is in the dwindling realm of the bumblebee. As a pair of videos published with a new Science study show, certain insecticides may not kill the bees outright but instead inflict a social toll that’s subtle but ultimately could be so devastating that immediate death might be preferable.

The two videos highlight the disturbing effects of a traditional insecticide called imidacloprid on a colony of bumblebees kept in a lab. Imidacloprid, a nicotine derivative that has been available since 1994, prevents nerves from transmitting signals in the body. In humans, it can sometimes cause vomiting or dizziness. It’s useful as an insecticide because imidacloprid is fatally toxic to invertebrates.

Usually, sucking bugs like termites are its main intended victims. But unfortunately, bumblebees often wind up becoming collateral damage, as the videos above and below illustrate.

A pesticide meant for termites is affecting bumblebee social life, slowly killing the hive.

Unsplash / Jan Tinneberg

Bumblebees, useful pollinators with declining populations, are susceptible to the pesticide’s effects, but it doesn’t affect them in the same way that it does termites. The videos demonstrate its longer-lasting, sinister effects. First, it changes the way worker bees go about their main mission in life. Second, it takes a psychological toll on hive society, turning otherwise social and active worker bees to become motionless, isolated, and, some might say, despondent.

Video One: Giving Up on Work

A series of cameras monitored the movements of a group of ID-tagged worker bees in a simulated hive, tracking their interactions as they were dosed with varying concentrations of the pesticide. As the header video shows, the worker bees exposed to the pesticide did less foraging, the typical behavior in worker bees. As time elapsed, fewer and fewer bees ventured to the pollen section of their cage, neglecting their sole duty to the hive.

A map showing that bees exposed to higher levels of imidacloprid tended to stray farther from their queen. 


Video Two: Giving Up on Friends

The second video, shown below, shows that the pesticide-exposed bees “had reduced activity and nursing, were located farther from the nest center, and had reduced social interactions compared with controls,” as the team writes. In other words, the bees became antisocial.

Though it took the trained eye of bee researchers to first interpret the video, it’s possible to see what they see by keeping an eye on the bees tagged with red (exposed to 0.1 nanograms of the pesticide) and blue (exposed to 1 nanogram of pesticide). Compared to the green-tagged control bees, the pesticide-dosed bees tend to stray toward the corners of the frame as time elapses, as the map above helps illustrate.

The authors suggest that these behaviors, over time, can reduce brood growth or change the resource intake of the hive. This has led the team to suggest that the pesticide may be partially responsible for Colony Collapse Disorder — a disturbing phenomenon in which bees suddenly decide to abandon their hives mid-winter — though this connection has not been fully established.

Worryingly, the research shows that bees don’t need to be continuously exposed to imidacloprid to see these effects. In the paper, the team writes that “sub-lethal” effects can occur within 24 hours of exposure, and imidacloprid can linger for years in soil. In this way, the destruction it may impose upon a hive is slow and steady, destroying the social fabric of bee society until every member dies.