Bees Use Drugs? Evidence of Self-Medication

Photo © Leif Richardson

Since the 1970s, scientists have documented animals engaging in self-medication, or the consumption of plants and other natural resources in their native environments to combat parasitic infections. Many animals, from neurologically complex mammals, like the Ethiopian Baboon, to less neurologically complex insects, like the Fruit Fly (Drosophila melanogaster), engage in self-medicationopen_in_new, so it is not surprising that growing evidence points to bees’ participation in this practice as well. In fact, previous researchopen_in_new documented honey bees increase their foraging of antibiotic plant resins when under stress from fungal pathogens. Could more access to certain plants provide some solutions for decreasing bee populations?

bombus vagans turtlehead1

Photo © Leif Richardson

Recent researchopen_in_new by scholars at Dartmouth, University of Colorado at Boulder, and North Carolina State University investigated the use of secondary metabolites called iridoid glycosides–specifically, aucubin and catalpol–use by the native eastern bumble bee, Bombus impatiens, infected with Crithidia bombi, an intestinal parasite. These parasites shorten the bee’s lifespan and limit the productivity of the queens, both of which negatively impact bee populations.

deer eating

Photo © Jen Goellnitz

Secondary metabolite compounds serve important ecological functions. Plants contain secondary metabolites, like iridoid glycosides, in the leaves and flowers. Because they are toxic to some herbivores (while some animals just find them distasteful), plants that have these compounds often receive some protection from animals that would normally eat them. At the same time, the pollinators who feed on the nectar of these plants seem to receive some relief from parasitic infections. Researchers found that the bees that had parasitic infections of Crithidia bombi spent up to three timesopen_in_new longer foraging on plants with beneficial secondary metabolites than uninfected bees. Moreover, laboratory experiments documented that the parasite load was reduced by 61-81% open_in_new in individuals when infected bees were fed some secondary compounds.

honey bees

Photo © Irene Florez

It is possible that one environmental pressure currently responsible for declining bee populations is parasitic infectionopen_in_new. The researchers go so far as to suggest that understanding the chemistry of bee diets could, at least, provide missing information in the mystery of pollinator declines and suggest ways that people can support bees’ “self-medication” efforts through targeted plantings.

self medicating

Photo © Leif Richardson

While there are many species of plants that contain iridoid glycoside in their leaves (see the box at the end of the article for examples), there are very few plants that have been found to contain iridoid glycoside in their flowers and nectar. This particular study of eastern bumble bees focused on the White Turtlehead (Chelone glabra), a plant native to North America, and one of the only known to date to contain this secondary metabolite in flower nectar.

field of flowers

Photo © Clare Bell

Though more research needs to be conducted, it has been suggested that one of the pressures negatively affecting pollinators is the loss of native habitat. It may be that this native habitat not only provided optimal forage for pollinators, but also provided all the necessary “medicinals” bees are adapted to use in the fight against parasites. Removing habitat would make it more difficult to find both food and the secondary metabolites traditionally used to fight potentially devastating parasitic infections.

bee hive

Photo © Susy Morris
Secondary Metabolite Plants
While research continues to unravel the complexities of declining populations of native and non-native bees, there is mounting evidence that home gardeners can help by planting and encouraging native flowers. Adding plants with known secondary metabolites to the mix can’t hurt, so we’ve compiled this reference list for planting ideas.
Consider adding some of these to your gardens.

1. Contains iridoid glycosides in the nectar of flowers, not just the leaves.
White Turtlehead (Chelone glabra)

2. Plants whose flowers contain other beneficial secondary metabolites.
Basswood Trees (Tilia)
Mint Family (Lamiaceae or Labiatae)

3. Plants containing secondary metabolitesopen_in_new in their leaves, whether their flowers and nectar contain iridoid glycosides is not yet known. If you click on each of these families, we have linked them to the Lady Bird Johnson Wildflower Center that lists native plants of North America, where you can explore your local options for including these plants in your gardens.
Apocynaceae
Asteraceae
Bignoniaceae
Buddleiaceae
Callitrichacea
Cornaceae
Hippuridaceae
Lentibulariaceae
Loganiaceae
Orobanchaceae
Plantaginaceae
Scrophulariaceae
Verbenaceae

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