D.U.I. Fly

How fruit flies self-medicate with alcohol

Good Medicine: Fruit fly larvae appear to consume alcohol on purpose to kill parasitic wasp eggs.
Carol Clark

Looks like humans aren't the only ones to discover the benefits of alcohol.

Fruit flies that consume alcohol when infected with a blood-borne parasite greatly increase their survival rate, Emory researchers found.  “We believe our results are the first to show that alcohol consumption can have a protective effect against infectious disease, and in particular against blood-borne parasites,” says Todd Schlenke, the evolutionary geneticist who led the research.

The study, coauthored by Emory graduate student Neil Milan and undergraduate Balint Kacsoh and published in Current Biology, adds to the growing body of evidence that some animals use toxic substances found in nature as medicine.

The Schlenke lab used Drosophila melanogaster, the common fruit fly, to study how immune systems adapt to pathogens. The fly larvae eat the fungi and bacteria that grow on overripe, fermenting fruit. “They’re essentially living in booze,” Schlenke says. “The amount of alcohol in their natural habitat can range from 5 to 15 percent. Imagine if everything you ate and drank all day was five percent alcohol. We wouldn’t be able to live like that, but fruit flies are really good at detoxifying alcohol.”

Tiny, endoparasitoid wasps are major killers of fruit flies. The wasps inject eggs inside the fruit fly larvae, along with venom that aims to suppress their hosts’ immune response. If the venom is effective, the wasp egg hatches and the wasp larva begins to eat the fruit fly larva from the inside out. Eventually, an adult wasp emerges.

Some fruit flies, however, can overcome the effects of wasp venom and kill the eggs, allowing the fly larvae to grow into adults. “A constant coevolutionary battle is going on between the immune systems of the flies and the venoms of the wasps,” Schlenke says. “Any new mechanism of defense that protects flies from wasps will tend to spread through fly populations by natural selection.”

Schlenke wondered if the fruit flies could be tapping the toxic effects of alcohol in their natural habitat to fight off wasps. To test the theory, the researchers used a bisected petri dish filled with yeast. One side was mixed with 6 percent alcohol, while the other remained alcohol-free. Most of the infected larvae ate from the alcohol side, and 60 percent were successful in killing the wasp eggs.

“The wasps aren’t as good as the flies at handling alcohol,” Schlenke says.

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