The disease is caused by a protozoan parasite called Ophryocystis elektroscirrha. The parasite invades the gut of the caterpillars and then persists when the caterpillars become adult monarchs.
Project leader Jaap de Roode in eScience Commons today said, “We have shown that some species of milkweed, the larva’s food plants, can reduce parasite infection in the monarchs. And we have also found that infected female butterflies prefer to lay their eggs on plants that will make their offspring less sick, suggesting that monarchs have evolved the ability to medicate their offspring.”
(Images: Jaap de Roode and Lisa Sharling)
Adult monarch butterfly
De Roode, assistant professor of biology at Emory University, said, "“We believe that our experiments provide the best evidence to date that animals use medication."
Jaap de Roode, who discusses his latest findings in this video
At Discovery News, we've touched on the topic before for other species. Spider monkeys, for example, are thought to have discovered a medicated body scratcher. But there are relatively few such studies on self-medication by animals.
(A sick monarch butterfly dying from the parasite)
In this case, there's added interest because the behavior is enacted by a creature that, despite its beauty, is fairly low on the food chain. Plus, the behavior is trans-generational, says Thierry Lefevre, a post-doctoral fellow in de Roode’s lab. “While the mother is expressing the behavior, only her offspring benefit.”
Health-related decisions made by non-human species could also potentially benefit us in future. For example, researchers like chemical ecologist Mark Hunter have been studying milkweed plants to determine their medicinal properties.