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It turns out well-fed bees are better able to fight off harmful effects of parasites

February 24, 2016

3 Min Read

A new study from Oregon State University shows that well-nourished honey bees are better off fighting a microscopic parasite that weakens their immune systems. The finding was published in the Journal of Insect Physiology and suggests giving honey bees access to a greater quantity and variety of pollen - their only source of protein - could give them a leg up in fighting the impact of the parasite.

In a media release detailing the study, Ramesh Sagili, a professor and honey bee Extension specialist at OSU, says "we found that bees fed a high pollen diet had better survival, even though the same diet also enhanced the reproduction of the pathogen."

Sagili and Cameron Jack, a doctoral student in horticulture, studied European honey bees - the most common species used to pollinate crops in the U.S. Bees were fed varying amounts of wildflower pollen, then exposed to a single-celled microsporidian, a fungus-like organism called Nosema ceranae that lives in the bees' digestive systems.

When the pest is available at high levels it disrupts protein metabolism, weakens immune systems and causes malnourishment in the next generation of bees. And a severe infestation can deplete the population of bees within a colony and may eventually cause it to collapse.

In the study, one group of bees ate an all-pollen diet, as did a control group not exposed to the parasite. Three other groups ate pollen mixed with non-nutritive cellulose in successively leaner ratios, with one part pollen to one, two and three parts cellulose. The fifth group got cellulose only.

After 16 days the researchers got a surprise. Bees fed the high-pollen diets had significantly more N. ceranae spores in their gut tissues. However, these bees were also in better shape overall than the ones fed on lower pollen diets. The bees also survived longer and had more protein in their hypopharyngeal glands - the structures in their heads that transform pollen into food for larvae.

Sagili says that "it may seem counterintuitive that the protein from the pollen enhanced the reproductive of the pathogen. But the important point is that the bees were able to compensate for its negative effects."

The impetus of the study came from Extension constituents. Many Oregon beekeepers use preventive antibiotic treatments to treat for N. ceranae and a related parasite - N. apis. These beekeepers worry that these treatments may do more harm than good.

Sagili also notes the treatment is expensive, especially if you don't know whether bees have the pathogen. "It's also troublesome because the treatment is a broad-spectrum antibiotic that could be causing other problems, such as killing the beneficial gut flora that help bees digest their food."

One concern is that too much protein can also be harmful to bees. "It appears that there is an optimal balance of nutrients needed for best survival. We now need to do some trials in the field to determine how much protein is optimal," Sagili says.

Source: Oregon State University

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