Understanding Honeybee Diseases

Health and social structure play role in crop production.

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By Marlene Cimons, National Science Foundation

Virtually all living things, from the smallest organisms to humans, are vulnerable to infectious diseases. Most humans know they have to stay away from other infected people if they don’t want to get sick themselves. But how does nature figure it out?

The social behavior of honeybees may provide some important clues.

“The bee society is a complex society, and they get a lot of diseases naturally,” says Dhruba Naug, associate professor of biology at Colorado State University.  “Evolution and natural selection must have played a role in creating a social structure responsive to the threat of diseases. If you can understand the behavioral mechanisms that restrict the spread of disease, including how their social structure and contact network looks like, maybe you can gain an understanding of how such processes work in other complex societies, including humans.”

Honeybees, especially older ones, can discriminate well between different odors.  Older bees tend to cluster with other bees that smell like them. This allows these older bees, who forage, increasing the likelihood they will bring back an infectious agent from the outside, to restrict disease among them.

But things change once they become sick.

“Infectious agents often drain the host of nutrients, and hosts need energy to fight these infections, so when a bee is sick, it becomes hungry,” Naug says. “Hunger alters their smell, just like we have keto smell [the bad breath caused by hunger or exercise] when we’re starving. And this makes sick and hungry bees drawn to other sick and hungry bees, while healthy and well-fed bees hang out with other healthy and well-fed bees. And, once again, this might restrict the spread of a disease.”

In other words, because hungry bees are sick bees, they tend to interact with other sick bees that smell like them, and avoid the healthy bees that don’t smell like them. “Maybe that’s nature’s way of preventing disease transmission,” Naug says.

Naug is studying the social structure of bees and its influence on disease transmission under a National Science Foundation Faculty Early Career Development (CAREER) award, which he received in 2009 as part of NSF’s American Recovery and Reinvestment Act. The award supports junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education and the integration of education and research within the context of the mission of their organization. NSF is funding his work with about $650,000 over five years.

His findings could prove significant, since bees are critically important to the nation’s agriculture. Bee pollination represents $15 billion in added crop value, particularly in specialty crops, such as almonds and other nuts, berries, fruits and vegetables, according to the U.S. Department of Agriculture. Moreover, about “one mouthful in three” in the human diet directly or indirectly results of honeybee pollination, according to USDA.

“Understanding the influence of social structure on honeybee diseases makes this study timely to address the recent concern about the health of honeybees, a topic of national importance, but also important for extending our still incipient knowledge of biological networks in general,” Naug says.

The health of honeybees has been declining since the 1980s, as a result of new pathogens and pests, as well as well as to the mysterious phenomenon known as Colony Collapse Disorder, in which worker bees suddenly disappear from a beehive or colony, and never return.

“We use the bee colony as a model of complex social structure to see how a disease might be expected to spread in a social group,” Naug says.  “I’m not suggesting that a bee society mirrors a human society--there are a lot of differences--but you can get an understanding of the basic processes involved in spreading a disease. Also, you cannot obviously examine these processes from an experimental standpoint in humans.”

Naug and his students infect their bees with Nosema, a fungus that afflicts the gastrointestinal system, causing diarrhea. By infecting bees with a model pathogen, they can observe how it changes the behavior of the bees as a result of the infection.