Diseases Wreak Havoc on Hives

This article is part of Seed World’s ongoing Protecting Pollinators series, brought to you by Bayer CropScience. Here, you’ll discover the answers to help improve bee health stewardship as researchers uncover them. In this article, you’ll learn about two prevalent diseases that affect honeybee health. Plus, experts provide tips to help diagnose the presence of disease in honeybee hives.

Without honeybees, it’s estimated that food production would significantly decrease. For this reason, many states, companies, universities and organizations have been putting resources toward protecting pollinators from a myriad of threats, including diseases.

For the 2013-14 winter, apiarists reported that 23.2 percent of managed honeybee colonies in the United States died, according to a Department of Agriculture report done in collaboration with the Bee Informed Partnership. During the past six years, winter losses have been averaging about 30 percent, reports USDA. This rate threatens the viability of beekeeping operations.

Two of the most prominent diseases in hives are European foulbrood and American foulbrood, says Sarah Myers, apiarist and event manager for Bayer CropScience in Research Triangle Park. She explains that both diseases are bacterial and have been plaguing bees since the early 1900s. Myers says American foulbrood (Paenibacillus larvae) is extremely contagious.


Honeybee larvae infected with American foulbrood become a stringy mass of material that later dries and carries the spores that might infect other larvae.

Rob Snyder, a University of California Extension crop protection agent, says American foulbrood is introduced to the hive by drifting bees from nearby colonies and infected equipment, tools and clothing. “The infection begins when spores enter the hive, and then food contaminated by spores is fed to the larvae by nurse bees,” Snyder says. “Once spores are in the midgut, the bacteria take over using the larvae as a source of nourishment. After the cells are sealed, death occurs.”

Jamie Ellis, a University of Florida assistant professor of entomology, says American foulbrood is not easy to diagnose. Ellis provides a few tips for diagnosing American foulbrood in hives.

“American foulbrood infects larvae, but infects prepupa or pupa,” he explains. “If you look at a healthy cell from a side-view, it typically has a dome shape. But with an infected hive, the cell caps are usually perforated or sunken. This is the first sign to a beekeeper that there might be a problem.” For beekeepers who see punctured, sunken cells, Ellis recommends removing them and looking inside the cell. “American foulbrood kills living bees and they shrivel and fall to the bottom of the cell,” he says. “You can pull the cell out and tilt it so you are looking at the bottom of the cell to see the scales.”


At the Bee Research Lab in Beltsville, Maryland, entomologist Jay Evans studies the effects of bacterial pathogens on honeybee health and survival.

Two other indicators are the presence of a “tongue” and the ropy test. “Its not really a tongue,” Ellis says, explaining that as the bee shrivels, it leaves behind part of its anatomy looking like a tongue. “For the ropy test, find one of those punctured cell caps and remove it. Find a stick or piece of straw and stir it in the cell. When you pull it out, if there’s a ropiness or stringiness, that’s an indicator.”

Unlike American foulbrood, European foulbrood (Melissococcus plutonius) is not as contagious or detrimental to hives, Myers says.

It’s often found when nectar flows are sporadic or there is an insufficient number of nurse bees to attend the brood, adds Snyder, who says it’s transmitted when bacteria become mixed with the bee bread, nectar or diluted honey, and then fed to larvae.

European foulbrood affects the larvae and kills it in about four to five days. This disease does not create spores, meaning once it disappears it’s gone, Ellis says, noting that bees can typically take care of themselves and make it through if they have good honey coming in.

A healthy honeybee larvae typically lies in the bottom of a cell in the shape of a “C” — that’s why they’re called C larvae, Ellis says. Healthy larvae are white or light-colored and have a shiny appearance. When infected with European foulbrood, the larvae turn yellow and brown, loose their shiny appearance and are twisted in their cell. They also have a rank smell.

Many states have state apiary inspection programs that can help beekeepers inspect for the presence of American foulbrood or European foulbrood.

“Honeybees can’t successfully survive naturally in the wild,” Myers says. “It’s up to beekeepers to properly manage them, and I know firsthand that it’s very difficult.”

jun14_pollinators_thm June 2014: A New Hive for Bee Care Research
feb14_pollinator_thm February 2014: Protecting Pollinators Resource Guide