Chemicals found in flowers of some plants are a "natural medicine cabinet" for ailing bees infested with one common intestinal parasite, a study has found.

The naturally occurring chemicals, which plants produce to protect themselves against predators, have also been shown to be beneficial for bees that consume them along with the flowers' nectar, research led by Dartmouth College has shown.

In experiments, infected eastern bumblebees showed reduced levels of the Crithidia bombi parasites in their gut after 7 days of consuming the natural plant toxins as they gathered nectar.

Infection levels in the bees, Bombus impatiens, were down by more than 80 percent at the end of the experiment, researchers said.

Crithidia can shorten the lifespan of individual bees and can reduce the queen production in a colony.

"We found that eating some of these compounds reduced pathogen load in the bumblebee's gut, which not only may help the individual bees, but likely reduced the pathogen Crithidia spore load in their feces, which in turn should lead to a lower likelihood of transmitting the disease to other bees," says evolutionary ecologist Lynn Adler at UMass Amherst.

The findings suggest growers who depend on bees and other pollinators might want to consider planting hedgerows or gardens with plants that produce such natural herbal remedies, the scientists say.

"Because plants just sit there and can't run away from things that want to eat them, they have evolved to be amazing chemists," says Adler.

The biological compounds they produce throughout their stems and leaves to protect themselves are known as secondary metabolites, chemicals not involved in either reproduction or growth, she explains.

"They are amazing in the diversity of what they can produce for protecting themselves or for attracting pollinators," she says.

The compounds are present in the nectar and pollen of the plants too, the researchers have determined, which makes them readily available for bees to gather and consume.

"Having bees consume these protective chemicals could be a natural treatment of the future," says Adler, who points out that commercial honeybee operations are already using one such chemical extracted from thyme to treat infestations of mites in honeybee hives.

The plant chemicals analyzed for the study included nicotine and anabasine, both present in the nectar of flowers in the tobacco family; caffeine in coffee and in citrus nectar; amygdalin from almond tree nectar; catalpol and aucubin from turtlehead flowers; gallic acid from buckwheat nectar, and thymol from basswood tree nectar.