Flies Infected With Parasites Drink Alcohol as an Antibiotic

By Sarah Zhang | February 16, 2012 12:24 pm

spacing is important
Fruit fly larvae and wasp

What’s the News: Fruit fly larvae have unusually high alcohol tolerance, which scientists used to think was because they happen to feed on yeast in rotting fruit. Turns out they’re in it for the alcohol, too—as medication. According to a new study*, alcohol protects them from the wasp parasites that lay eggs in fruit fly larvae.

How the Heck

  • Two groups of Drosophila melanogaster (fruit fly) larvae were fed food either with or without ethanol. Researchers observed that wasps are less likely to lay their eggs into larvae that have eaten alcoholic food.
  • When the wasps did lay their eggs in the alcohol-fed fruit fly larvae, they were less likely to survive. Dissections revealed that wasp larvae developing in the alcoholic environmental had abnormalities like inverted body parts.
  • Fruit fly larvae usually have a natural immune response to the parasite, but alcohol seems to be somehow suppressing that response while also killing the wasp parasite.
  • When the fruit fly larvae get infected, they actually crawl over to the side of the petri dish with alcoholic food. It’s like going to the drug store when you get sick.
  • There’s another neat twist to the experiment that tells a story about coevolution. The researchers looked at two different species of wasp parasites, one that infects D. melanogaster specifically and another that is a generalist. Alcohol is several times less effective against the specialist wasp than the generalist one. This suggests that the specialist wasp too has evolved high alcohol tolerance so that it can keep parasitizing the D. melangaster that are trying to kill them with alcohol.

What’s the Context:

  • Despite what certain human drinkers out there may claim, these are the first results that show any organism successfully self-medicating itself with alcohol against infection. It’s possible alcohol has protective effects in or against other organisms too.
  • So should you nurse your sore throat at the bar? This study on wasp parasites in fruit flies can’t tell you, a human, what to do. Heavy longterm drinking damages the immune system (pdf) but observational studies suggest drinking red wine may help prevent colds.

The Future Holds:

  • Future research will want to figure out the mechanisms for how it all works: how alcohol kills wasp parasites, how wasps know to avoid liquored-up larvae, how alcohol changes larval immune response, how infection makes larvae seek out alcohol. This study has observed lots of neat things—now we want to know how they happen.
  • The other burning question, of course, is: does this work for any other organisms?

Reference: Milan NF et al. Alcohol Consumption as Self-Medication against Blood-Born Parasites in the Fruit Fly. Current Biology. 20 March 2012. DOI: 10.1016/j.cub.2012.01.045

Image courtesy of Milan et al, Current Biology

* Does this link not work? See Ed Yong’s explanation of this unfortunate quirk of science publishing.

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