Pesticide exposure makes it harder for bees to walk in a straight line


Bees, long despised for stinging humans and pets, but loved by horticulturalists for their life giving goodness, are under attack like never before.

In June research identified a dangerous variant of the deformed wing virus is on the rise worldwide. The virus infects honeybees, causing their wings to atrophy and the animals to die.

Also that month the varroa mite, a major honeybee parasite, was discovered in biosecurity surveillance hives at the Port of Newcastle.

Now new research has identified what happens to bees when they are subject to insecticides.

Have you ever struggled to walk in a straight line after having one too many? Well, it seems that honeybees are having similar issues but after getting a dose of insecticides.

“Here we show that commonly used insecticides like sulfoxaflor (kills aphids and lygus) and the neonicotinoid imidacloprid (pesticide that protects seeds of field crops) can profoundly impair the visually guided behaviour of honeybees,” said lead author of a new study, Dr Rachel H Parkinson from the University of Oxford.

“Our results are reason for concern because the ability of bees to respond appropriately to visual information is crucial for their flight and navigation, and thus their survival.”

Insects have an innate ‘optomotor response’, which lets them orient themselves back onto a straight trajectory if they steer off-course while walking or flying.

The research, published in Frontiers in Insect Science, challenged this optomotor response of walking honeybees by putting them in front of video screens of vertical lines which tricked them into thinking they’d moved off course.

The vertical bars would move from left to right, or right to left which ‘tricks’ the bee into thinking it’s been blown off-course and needs to perform a corrective turn.

The team of researchers looked at four groups of between 20-30 bees. The control had access to normal sugar water to drink, while the other three had different forms of insecticides added. One group had 50 parts per billion of imidacloprid, another had 50 parts per billion sulfoxaflor, and the last had 25 parts per billion of imidacloprid and 25 parts per billion of sulfoxaflor together.

Unfortunately, the bees which had been exposed to the insecticide performed worse as they turned to get back on track. Bees exposed to pesticides seemed to have shallower turns and sometimes only turned one way. The asymmetry between left and right turns for example was 2.4 times greater for those bees exposed to pesticides.

After this experiment, the researchers then had a look at the bee brains to look at the damage. Using molecular techniques, the team found that pesticide-exposed bees tended to have an elevated proportion of dead cells in parts of the brain’s optic lobes, which is important for processing visual input.

Key genes for detoxification were also dysregulated after exposure. However these brain changes were relatively weak and highly variable across bees, and unlikely to be the sole explanation for the strong visual issues in the original experiment.

“Neonicotinoid and sulfoximine insecticides activate neurons in the insect brain and are not always recycled fast enough to prevent toxicity,” said Parkinson.

This research comes on the heels of a slew of other research in recent years suggesting that pesticides impair baby bee brain development, or it can make them antisocial and lazy, and many scientists are asking for them to be banned.

Cosmos, 18 August 2022