Class of Pesticides Found to Make Bees Less Social

(CN) – Scientists said Thursday they’ve found that exposure to the neonicotinoid pesticide imidacloprid produces complex changes in the social behaviors and activities of bumblebees – a very bad thing for creatures who rely on their colonies to survive.

Neonicotinoid pesticides are nicotine-like chemicals which attack the nervous systems of pests. First widely used in the 1990s, “neonics” are effective against a wide range of different pests and all act in a similar manner. They are water-soluble and can be absorbed by plants and distributed through their tissues. When insects feed, the substance binds to and blocks neurotransmitters in the central nervous system, leading to overstimulation that causes paralysis and eventually death.

Because neonics aren’t harmful to mammals in the dosages used for pesticide use, they were originally thought to be safer than traditional pesticides particularly since they eliminate the need for multiple applications of pesticides known to be toxic to mammals.

But in recent years, studies have emerged indicating that the trace quantities of neonicotinoids remain present in pollen and nectar of plants and affect pollinators such as bees and butterflies. Nearby crop and wild plants can also be contaminated and the insecticides can accumulate in soil. Neonics have been detected in streams, honey, garden flowers and wildflowers.

There is evidence that exposure to neonics has a negative impact on bee colonies, but the way that the pesticide affects the bees is not fully understood.

In a study released Thursday by the American Association for the Advancement of Science, scientists studied the effects of varying doses of imidacloprid on bumblebee colonies and found that exposure to levels most likely to be found in crops affected the social behavior of the bees in surprising ways.

Bumblebees exposed to imidacloprid became less social and spent less time together. The bees also spent less time nursing larvae, foraging and constructing the wax canopy which insulates and regulates the temperature of the hive. These findings match earlier studies, but by using an automated, robotic platform for continuous, multicolony monitoring of uniquely identified workers, the study found that the behavioral changes in the bees varied over the course of a day.

Behavioral changes appeared to peak at night and when the temperature was cooler. Bees exposed to field-realistic concentrations of imidacloprid experienced problems regulating temperature, which may have been exacerbated by a tendency to move to the edges of the nest rather than remain clustered together at the center.

The complex changes to bee behavior with neonic exposure highlight the value of using technology to examine the impacts of environmental changes not just on a large scale, but even down the hive.

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