Two Broad-Spectrum Insecticides May Contribute to Colony Collapse Disorder in Honeybees

Colony collapse disorder continues to impact bees across the United States and the world. As populations decline, though, scientists are struggling to come up with the reasons behind these bee deaths. Now, they may have found one of the impacts. It turns out that two broad-spectrum systemic insecticides, fipornil and imidacloprid, may be especially toxic to honeybees.

Honeybees are a huge part of the agriculture industry. The cross-pollination services that they provide are required by about 80 percent of all flowering plants. In fact, about a third of all agriculture food production directly depends on bee pollination. This makes it crucial to understand what types of chemicals are affecting declining bee populations.

A key characteristic of colony collapse disorder is the incapacity of the honeybees to return to their hives. Since the effects of pirazoles (fipronil) and neonicotinoids (imidacloprid) on the nervous system are fairly well documented, the scientists believed that these insecticides may play a role in causing this phenomenon. Yet they had to test it first.

The scientists examined the effects of fipronil and imidacloprid on the bioenergetics functioning of mitochondria isolated from the heads and thoraces of Africanized honeybees. Mitochondria are the power plants of a cell, supplying energy to help power the cell's day-to-day functions. Honeybee flight muscles are actually highly dependent on high levels of oxygen consumption and energy, so studying the mitochondria gave researchers a good understanding of how these pesticides might affect bees.

"If something goes wrong, the energy production is impaired," said Daniel Nicodemo, one of the researchers, in a news release. "Similar to a plane, honeybees require clean fuel in order to fly."

In the end, the researchers found that both fipronil and imidacloprid negatively impacted the mitochondrial bioenergetics of the head and thorax of the honeybees. In fact, even a low level exposure contributed to the inability of a honeybee to forage and return to the hive.

The findings reveal yet another risk to honeybees that should be monitored. Because these chemicals may be contributing to declining bee populations, it's important to potentially restrict their use in areas where hives are located.

The findings are published in the journal Environmental Toxicology and Chemistry.