Honeybees Can't Walk Straight After Pesticide Exposure

After flitting about on pesticide-covered flowers, honeybees are so affected they can’t move in a straight line. Researchers have found insecticides severely damage the insect’s nervous system.

Exposure to many pesticides has been shown to negatively impact the behavior of honeybees and the toxic chemicals can lead to the death of individual bees or entire hives.

In the new study, scientists examined the impact of insecticides like sulfoxaflor and imidacloprid, a neonicotinoid, and how they can impact a honeybee’s ability to navigate easily.

“My previous research showed that locusts exposed to insecticides do not steer or jump to avoid collisions and that this results from effects on their ability to see object motion,” lead author Rachel Parkinson, a scientist at the University of Oxford, tells Treehugger.

“I wanted to know if there were similar effects on wide-field motion in honeybees, as they use this type of visual information for flight stabilization and navigation. I hypothesize that this may be a contributing factor to colony collapse disorder by which bees exposed to pesticides have a hard time finding their way home.”

Colony collapse disorder was first noted in the early 2000s with a dramatic drop in bee populations. Some beekeepers reported losses of 30 to 90% of their hives. The queen and young remained while many of the worker bees just disappeared. The colony is unable to survive without so many workers.

Bees in Virtual Reality

A healthy bee has what is known as “optomotor response,” which helps them turn back into a straight path when something works to veer off when they are flying or walking.

“The optomotor response is a reflex-like behavior by which animals will instinctually turn to follow a rotating visual scene,” Parkinson says. “Its purpose is to help the animal regain and maintain a stable orientation. 

For their study, first, researchers exposed bees in a laboratory to various mixtures of insecticides mixed in sucrose for five days. Then they tested the insect’s optomotor response by attempting to visually trick them as they walked.

They played videos that showed vertical bars moving from side to side on two screens in front of the bees. The moving bars make the bee think it has been blown off course and needs to turn in order to get back on a straight path.

“I tested the bees in a type of virtual reality, where they could walk on a ball treadmill while being shown wide field motion that looked like it was rotating around the bee,” Parkinson says.

Bees that were not treated with pesticides performed well in the optomotor environment, reorienting themselves in a straight line. They righted themselves and flew or walked straight when exposed to different speeds.

However, the bees that were exposed to pesticides didn’t fare as well. 

“Some bees responded to motion in one direction only, turning only one way and not switching direction when the motion switched direction, and other bees did not perform turning maneuvers at all,” Parkinson says. “I was surprised by the severity of the effects, especially for the sulfoxaflor pesticide treatment group as the dose I used was a field-relevant concentration.” 

The results were published in the journal Frontiers in Insect Science.

Profound Sublethal Effects

Pesticides have long been shown to have a toxic effect on honeybees.

“There are many many documented effects of pesticides on bees, ranging from effects on reproduction, learning, and memory, foraging efficiency, etc.,” Parkinson points out. “Some studies have shown that exposed bees take longer to return to the hive when foraging, or when captured and released at a new location.”

The new findings help researchers continue to understand the dangerous impacts of these chemicals, which could lead to better protection and conservation.

“It’s important to understand the range of sublethal effects of pesticides and mixtures, as often these happen at doses that are much lower than those required to directly cause death—the message is (not just from my study, but from many studies!) that sublethal effects can be profound and are likely to reduce the survival of bees overall,” Parkinson says.

“It is, however, important to do more research to determine whether the effects I observed in walking bees would translate to flying bees.”