Sick bees self medicate say researchers

Sick bees in the wild seek out plants with medicinal substances say researchers in a Dartmouth-led study.

Infected with a common intestinal parasite, wild bumble bees native to North America sought out plants with a group of metabolites called iridoid glycosides. In addition to deterring deer from eating plants that contain these substances, iridoid glycosides appear to reduce the number of parasites affecting bees that forage on their nectar, thus in effect treating them for their disease.

The full findings of the study conducted by researchers from Dartmouth College and the University of Colorado-Boulder appear in the September edition of the scientific journal, Ecology.

In previous studies in the lab, researchers found that certain plant substances known as alkaloids, glycosides, terpenoids and phenolics, which are poisonous to humans and other animals, significantly reduced the disease load of bumble bees.  They then followed up on their exploration to see if bees foraging in the wild would seek out the plants rich in these substances.

"We found that parasitized bees preferentially visited flowers containing the highest concentrations of iridoid glycoside compounds that can reduce bee parasites, but healthy bees either made no distinction between flowers with different concentrations of nectar chemicals or avoided those with highest concentrations," says lead author Leif Richardson.

The research team specifically looked at Chelone gabra, commonly known as snake's head or white turtlehead. It grows in North American wetlands and blooms from midsummer to fall with a white, clenched flower that pollinators must pry open to reach into.

Although Chelone isn't found in Texas, Richardson says "many types of plants, including those found in Texas, produce nectar and pollen containing plant chemicals that can reduce bee parasite loads. " Two examples he gives are tobacco and Gelsemium sempervirens, also known as Carolina Jasmine.

Native bees and imported honeybees face an increasing number of threats, from widespread pesticide use to loss of habitat and forage land. Although what this study has found doesn't offset these challenges, it does offer insight into how bee populations may be helped by preserving and increasing the diversity of flowering plants in the wild.