Bee brains affected by modern pesticides

In a startling revelation, researchers have said in a study that currently available common pesticides affect bees greatly to the point that there is brain damage which affects their sense of flying properly.

Researchers say that modern pesticides like sulfoxaflor and the neonicotinoid imidacloprid damage the nervous system of honeybees so that it becomes hard for them to walk in a straight line. The results are published in Frontiers in Insect Science. The findings are important as they show insecticides are affecting the ability of bees to respond appropriately to visual information is crucial for their flight and navigation, and eventually their survival.

Optomotor response keeps insects in line

Insects have an innate ‘optomotor response’, which lets them orient themselves back onto a straight trajectory when they threaten to steer off-course while walking or flying. Researchers challenged the optomotor response of walking honeybees to respond accurately and timely to videos of vertical bars that moved from left to right, or vice versa, across two screens in front of them. This ‘tricks’ the bee into assuming that she has suddenly been blown off-course and needs to perform a corrective turn to return to a straight path. A healthy optomotor response will then instruct the bee’s motor system to orient back to an illusory straight line mid-way between the optic flow from right and left.

The researchers compared the efficiency of the optomotor response between four groups of wild-caught forager honeybees, with between 22 and 28 bees tested per group: each had been allowed to drink unlimited 1.5 molar sucrose solution over five days, either pure or contaminated with 50 ppb (parts per billion) imidacloprid, 50 ppb sulfoxaflor, or 25 ppb imidacloprid and 25 ppb sulfoxaflor simultaneously.

Optomotor response worse after exposure to pesticides

All bees were less good at responding to the simulated optic flow when the bars were narrow or moving slowly (ie, seemingly far away) than when they were wide or moving fast (ie, seemingly close by). But for any width and speed, the bees who had ingested the pesticides performed poorly compared to control bees. For example, they turned quickly in one direction only and didn’t respond to changes in the direction of movement of the bars, or showed a lack of turning responses. The asymmetry between left and right turns was at least 2.4 times greater for pesticide-exposed bees than for control bees.

Minor brain damage

The researchers also show with molecular techniques that pesticide-exposed bees tended to have elevated proportion of dead cells in parts of the brain’s optic lobes, important for processing visual input. Likewise, key genes for detoxification were dysregulated after exposure. But these changes were relatively weak and highly variable across bees, and unlikely to be the sole explanation for the observed strong impairment of the optomotor response.

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