Manganese Drastically Impacts Honeybee Behavior

Honeybee populations are still declining. Now, scientists have found something else that may be impacting these insects. Manganese, which was once scarce in the environment, is now far more plentiful and may addle honey bees.

When people burn fossil fuels, mine and manufacture, they strew previously buried metals across the surface of the Earth. In this latest study, the researchers examined the effect of low levels of manganese, which is a common industrial pollutant, on the behavior of honey bees.

"We've known for a long time that high doses of manganese kill neurons that produce dopamine, causing a Parkinsonian-like disease in people," said Yehuda Ben-Shahar, one of the researchers, in a news release. "In insects, as well, high levels of manganese kill dopaminergic neurons, reducing levels of dopamine in the brain. But in this study we were looking at low-level exposure and we saw the opposite effect. Instead of reducing dopamine levels, manganese increased them. Increases in dopamine and related neurotransmitters probably explain some of the abnormal behavior."

Trace amounts of manganese are essential for life. In fact, all living organisms rely on the chemical properties of this metal to drive reactions in cells and mop up the toxic byproducts of cellular life in the presence of oxygen. Too much in honeybees, though, can lead to severe consequences for the insects.

"We evolved in an environment where there was little manganese, and so we developed ways to pump it into our cells," said Ben-Shahar. "But now environmental levels are quite different from those to which we are adapted and we don't really know what that means for human health."

Low levels of manganese causes bees to advance through age-related work assignments faster than normal. However, they complete fewer foraging trips. This can have major consequences for colony health.

"When we try to understand pathologies, we often look at extremes," said Ben-Shahar. "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."

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