Mysterious Honey Bee Disease Key Factor in Colony Death

Domesticated honeybees have been disappearing from hives across the globe, infected by a little-known disease that has killed off entire colonies. Now, a long-term study of honey bee health has identified the disease and has found it to be the largest risk factor for predicting the death of a bee colony.

The study, published in the journal Preventative Veterinary Medicine, evaluated the health of 80 commercial colonies of honey bees in the eastern United States about once per month over the course of 10 months. These 10 months encompassed the working "season" for commercial bee colonies when they're used to pollinate flowers and produce honey. While observing the colonies, the researchers tracked changes in their health and attempted to determine what factors early in the year could have contributed to colony deaths. Over the course of the study, a total of 56 percent of the colonies died.

So what caused the deaths? After analyzing the various causes, the researchers found that a disease known as "idiopathic brood disease syndrome" (IBDS), which kills off bee larvae, made colonies 3.2 times more likely to die. It was the largest risk factor for bee colony death.

"Historically, we've seen symptoms similar to IBDS associated with viruses spread by larghe-scale infestations of parasitic mites," said David Tarpy, co-author of the paper describing the study, in a press release. "But now we're seeing these symptoms-a high percentage of larvae deaths-in colonies that have relatively few of these mites. That suggests that IBDS is present even in colonies with low mite loads, which is not what we expected,"

In addition, another occurrence known as the "queen event" made colonies 3.1 times more likely to die. Since colonies only have one queen, when a colony perceives that there's something wrong with its queen, it will try to replace her. However, this process is not always successful and sometimes lead to the death of the colony.

This study is the first of its kind to repeatedly evaluate the health of the same colonies over the course of a commercial season. It allowed researchers to understand what diseases put colonies most at risk, and highlighted what diseases scientists should focus on in the future.

"These are areas we are actively researchers," said Tarpy in a press release. "Hopefully, this will give us insights into other health problems, including colony collapse disorder.