A Common Industry Pollutant Is Turning Bees Into 'Bumbling Idiots'

The decline of pollinator populations, especially honeybees, has been something of an international crisis. Now, researchers are finding out exactly how some pollutants affect honeybees in a desperate bid to try to mitigate their harmful impact.

Much like mercury, the heavy metal pollutant known as manganese is often seen as a necessary evil in this modern industrial age. It is used in making steel, matchsticks, and even the batteries that power everyday life.

Also like mercury, emissions of this trace metal can slip into the atmosphere, where it can be picked up by growing plant life. And while both metals are strictly controlled in developed worlds, those trace amounts can still add up to harmful levels over time.

According to a study recently published in the journal Biology Letters, levels long considered safe for people can still impact pollinators. After accumulating in the nectar of contaminated plants, bees can unwittingly bring small amounts of manganese back to their hive, where it can be left to gradually build.

To see if this build-up could actually prove toxic to honeybees, Yehuda Ben-Shahar, a biological geneticist at Washington University in St. Louis, and his colleagues simulated a manganese exposed environment for a hive, feeding Apis mellifera trace amounts of the harmful mineral for four days. They then tested the brains of the bees, looking for anything out of the ordinary. (Scroll to read on...)

"We've known for a long time that high doses of manganese kill neurons that produce dopamine, causing a Parkinsonian-like disease in people," Ben-Shahar explained in a statement. "In insects, as well, high levels of manganese kill dopaminergic neurons, reducing levels of dopamine in the brain."

However, he added, "in this study we were looking at low-level exposure and we saw the opposite effect. Instead of reducing dopamine levels, manganese increased them."

The researchers compared their affected hive to a control group of honeybees and found that these subtle changes had a powerful and adverse effect on the hive's functionality as a whole. Contaminated worker bees advanced through age-related work assignments faster than normal, yet completed fewer foraging trips than the bees who were not exposed to manganese. They also proved less efficient when they did go out, seemingly bumbling around and taking far longer to gather food essential for a hive's survival.

The researchers remain uncertain as to why exactly the toxin's impact on dopamine production turns foraging bees 'dumb,' but they stress that there is an important lesson to be learned here.

"When we try to understand pathologies, we often look at extremes," Ben-Shahar said. "We tend to ignore more modulatory changes like this one and assume we don't need to worry about them. But that may be a mistake. The bees, which vacuum up everything in the environment, might be serving as an early warning indicator of an environmental toxin."

"Manganese is not the number one dangerous thing out there in the environment," he quickly added. "Nor do we know if it affects our brains the same way it does those of insects."

However, impacting humans or not, trace manganese is clearly hurting an exceptionally important ecosystem in ways never before considered - a hint that experts and regulators of harmful toxins need to pay closer attention to the natural world we all rely on.

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