The availability of nutritious pollen has decreased over the past decade, and researchers now suspect that what honey bees eat is disrupting the bacterial communities that reside in their gut — and, in turn, negatively affecting their health.
Early in their lives, honey bees acquire a specific set of gut bacteria, known as the gut microbiome, which is formed through contact with their hive environment and siblings. These beneficial bacteria reside in specific niches of the bees' digestive tract. In healthy bees, they maintain a crucial microbial balance that provides protection from pathogens.
But should that microbial balance undergo an unhealthy shift, or dysbiosis, pathogens begin to colonize the bees' gut and sickness sets in, setting the stage for the colony's demise, known as colony dwindling, acccording to researchers from the University of Arizona, the U.S. Department of Agriculture and Scientificbeekeeping.com.
Honey bees collect pollen, mix it with honey and salivary excretions, and store it in a preserved state (known as "bee bread") for future consumption. But when faced with pollen-poor environments, beekeepers must go from colony to colony and feed bees premixed portions of pollen substitute.
However, pollen substitutes have yet to match the nutrition and benefits of natural pollen. One possible route for improving pollen substitutes is to allow the honey bee to collect and store the substitute diet as though it were pollen, potentially extending its shelf life.
So, researchers fed bees one of four types of naturally collected diets: fresh or aged pollen, or fresh or aged pollen substitutes. Using modern DNA sequencing techniques coupled with measurements of development, the researchers identified the communities of bacteria that had colonized the bees' digestive tract and their relationship to overall bee health.
"In general, bees given fresh pollen or fresh substitute fared better than bees given pollen or substitutes that had been aged," says Patrick Maes, UA graduate student and first author of the study, which appeared online this month in Molecular Ecology.
"Bees fed fresh diets suffered fewer deaths, made better use of food energy for their growth, and had lower levels of gut pathogens, like Nosema, a notorious pathogen of honey bees," Maes says.
Likewise, he says, bees fed fresh pollen or pollen substitute had more beneficial gut bacteria, like Snodgrassella alvi, whereas bees that consumed aged pollen or pollen substitute had higher levels of the pathogen Frischella perrara. The shift in bacterial type was significantly related to increased mortality, decreased development and early establishment of the pathogen Nosema.
"Our results provide the first evidence that diet influences the honey bee gut microbiome and subsequently overall colony health," Maes says.
"There was a long-standing dogma that stored pollen became more nutritious for bees as it aged," says Kirk Anderson, lead scientist of the study. "Contrary to popular belief, the nutritional value of stored pollen, also known as bee bread, decreases over time, and the shelf life of the bee-collected pollen substitute diet is even shorter than that of stored pollen."
Now the researchers are looking at improving the substitute formulations or usage practices with a focus on the bees' gut bacteria.
"These findings provide a tool that researchers can now use for further research," Maes says. "We know if we can feed the bees an aged diet that induces dysbiosis, then we can further study the dysbiotic events and gain insight into what roles the gut microbiome members are playing in honey bee health."
The study was funded by the USDA/ARS Carl Hayden Bee Research Center of Tucson, the California State Beekeepers Association and ScientificBeekeeping.com.