Our Chemicals Are Killing Honey Bees' Sex Lives

If there’s a species that doesn’t need an unintentional dose of birth control, it’s the honey bee.

A new study, however, suggests two common neonicotinoid insecticides are not only shortening the overall lifespan of male honey bees, known as drones, but also inhibiting their ability to produce viable sperm.

The chemicals’ contraceptive effects, warn researchers from Switzerland’s University of Bern, could have “profound consequences for the health of the queen, as well as the entire colony.”

The study, led by Bern doctoral student Lars Straub and published Wednesday in the journal Proceedings of the Royal Society B, is the latest bit of bad news for the planet’s most important pollinators, which are facing an onslaught of threats.

“We know multiple stressors can affect honey bee health, including parasites and poor nutrition,” senior author Geoff Williams of the University of Bern and Agroscope said in a statement. “It is possible that agricultural chemicals may also play an important role.”

Male honey bees obtained from colonies exposed to thiamethoxam and clothianidin were shown to have live sperm counts 39 percent lower than those not exposed, according to the study. The findings, the researchers say, “demonstrate for the first time that neonicotinoid insecticides can negatively affect male insect reproductive capacity.”

Additionally, the study found that the lifespans of chemically exposed bees were reduced by roughly 32 percent, from an average 22 days to 15 days.

Despite increased efforts to reverse declining bee populations, U.S beekeepers lost 44 percent of their total colonies from April 2015 to March 2016, an increase of 3.5 percentage points over the previous year, according to the findings of an annual survey released in May. Known threats include the parasitic varroa mite, malnutrition from habitat loss and pesticides. 

As the authors note in a press release, the two neonicotinoids involved in the study are partially banned in Europe. In the United States, the Environmental Protection Agency is currently reviewing neonicotinoids after a study found the chemicals can impair bumblebees’ learning and memory and blunt their ability to forage. Preliminary risk assessments for thiamethoxam and clothianidin are scheduled for release in December.

Scientists are particularly concerned about declining bee populations because of the potential impact on food security. The insects pollinate 75 percent of the fruits, nuts and vegetables grown in the United States, and add at least $15 billion in economic value to the country’s agricultural industry.

Study co-author Peter Neumann said in a statement that the results “highlight the need for stringent environmental risk assessments of agricultural chemicals to protect biodiversity and ecosystem functioning.”