Bee genocide may have been caused by insecticides that make bees unable to walk in a straight line

When exposed to neonicotinoids, bees start to stumble — and that sent billions to their death

By Matthew Rozsa

Staff Writer

Published August 18, 2022 5:04PM (EDT)

Bumblebees on a yellow flower (Getty Images/nnorozoff)
Bumblebees on a yellow flower (Getty Images/nnorozoff)

The mysterious deaths of vast numbers of honeybees earlier this century was a portent to human civilization. Called "colony collapse disorder," and first identified in 2006, some beekeepers saw as many as half of their bees suddenly and mysteriously die. Because most of human agriculture is dependent on bees to fertilize and pollinate their crops, humans are, in a very real way, dependent on bees for our survival — perhaps even more so than we are dependent on the fruits of our own agriculture. After all, we can plant and grow fruiting plants, but those plants won't fruit without the help of pollinators. 

Colony collapse disorder was eventually linked to a class of man-made insecticides called neonicotinoids. As the name hints, neonicotinoids are chemically similar to nicotine, which itself is a natural insecticide. Besides being linked to plummeting bee populations, neonicotinoids evidently had effects further down the food chain — harming bird communities, seeping into national wildlife refuges and perhaps affecting human brain development. Chemists and laypeople alike have observed for years that neonicotinoids seem to damage nervous systems; it is simply a question of quantifying how that happens.

But while neonicotinoids were tied to colony collapse disorder, it was less clear precisely what the insecticide was doing to bees. Now, a new study has made that question a little easier to answer: honeybees which are exposed to neonicotinoids — as well as to a separate insecticide, sulfoxaflor — have a more difficult time walking in a straight line. In other words, it seems to intoxicate them in a way that makes them vulnerable. 

For honeybees, being able to walk or not walk in a straight line is a big deal. Honeybees communicate to each other using a waggle dance that depends heavily on choreography. Honeybees that have trouble maintaining a straight line will not be able to fly or navigate correctly, and will leave worker bees more vulnerable to fatal threats. As such, the tests had serious implications for the future of honeybee colonies.

"These insecticides act somewhat similarly to nicotine in the nervous system, in that they bind to the same type of receptor that nicotine does," Parkinson explained.

The scientists tested the bees' ability to engage in visually guided behavior, since this skill set is key to bees encoding and responding to what they see. That, in turn, allows them to "orient and stabilize themselves during flight, and also so they can navigate to and from the hive and foraging sites," Dr. Rachel Parkinson, a professor of zoology at the University of Oxford and the expert contact for the study, told Salon by email.

Parkinson noted, as a disclaimer, that the tests were on "walking bees," not ones that were mid-flight. "We still need to find out if similar effects are present in flying bees," Parkinson said.

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As for the tottering bees, the researchers found that the insecticides in question undeniably made it more difficult for them to maintain a straight path.

"These insecticides act somewhat similarly to nicotine in the nervous system, in that they bind to the same type of receptor that nicotine does," Parkinson explained. "However these insecticides cannot be broken down as easily as nicotine. When exposed to the insecticides, the neurons are over-excited and this can result in a variety of effects, including changes in receptor expression (as a preventative mechanism) and neurotoxicity (when the insecticides cannot be broken down)." The end result is that reactive oxygen species — a type of unstable molecule that contains oxygen and can wreak havoc inside cells — winds up being produced.

"These can damage neurons resulting in altered function or cell death (apoptosis)," Parkinson told Salon.

Jay Feldman, the Executive Director of a 501(c)3 nonprofit organization that was founded in 1981 to raise awareness about toxic pesticide use known as Beyond Pesticides, echoed the concerns of the study's authors when contacted by Salon.

"Like any organism, the sensory system enable the bee to function. If the brain function, as this study finds, is altered, the organism cannot function normally," Feldman wrote to Salon. "We know that similar effects to the nervous system occur in people with similar vulnerabilities."

"Bees are crucial to humans for the pollination services they provide," Parkinson explained. "Without bees, we simply cannot produce the volume of food we require, which would be a global crisis."

In addition to making it more difficult for bees to walk in a straight line, neonicotinoids are also linked to bumblebees losing the initiative to forage and to them foraging less effectively. Lab studies have also linked the insecticides to bees losing their sense of orientation. It has also been revealed through laboratory studies that this class of insecticide actually becomes more toxic during colder weather, with serious implications for bees' collective health during inclement seasons. Insecticide pollution is so severe that, when combined with factors like climate change, habitat loss and the loss of genetic diversity, American bumblebees are now categorized as "vulnerable" to extinction. 

"Once the most commonly observed bumblebee in the United States, the American bumblebee has declined by 89% in relative abundance and continues to decline toward extinction due to the disastrous, synergistic impacts of threats including habitat loss, pesticides, disease, climate change, competition with honey bees, and loss of genetic diversity," explained the Center for Biological Diversity in a statement at the time. "In the last 20 years, the American bumblebee has vanished from at least eight states, mostly in the Northeast, and it is in precipitous decline in many more. "

There are implications to the problem of insecticide pollution not just for bees, but for humans. 

"Bees are crucial to humans for the pollination services they provide," Parkinson explained. "Without bees, we simply cannot produce the volume of food we require, which would be a global crisis. It's therefore paramount to understand how anthropogenic activities are affecting bees and other pollinators so we can assess what changes need to be made."

By Matthew Rozsa

Matthew Rozsa is a staff writer at Salon. He received a Master's Degree in History from Rutgers-Newark in 2012 and was awarded a science journalism fellowship from the Metcalf Institute in 2022.

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Bees Colony Collapse Disorder Furthering Insecticide Neonicotinoids