Parasite-plagued flies self-medicate on booze

Ever been told to take a swig of whisky to ward off a cold? Boozing fruit fly larvae do something similar: they seek out alcohol to kill a parasitic wasp that lays its eggs in their bloodstream.

Before you reach for the bottle, though, the researchers who found the behaviour caution that flies are very different to us, and their results don't say anything about the health benefits of a hot toddy.

The discovery, made by Todd Schlenke and colleagues at Emory University in Atlanta, Georgia, is one of the few examples of self-medication known in insects ? and a rare health benefit for alcohol.

Fruit fly larvae are raised in rotting fruit and so are naturally resistant to the toxic effects of alcohol. They have evolved enzymes like alcohol dehydrogenase to tolerate the ethanol while getting their fix of fermenting yeast. The flies even have a taste for grapes and are commonly found in wineries.

Alcohol licence

Schlenke and his team raised healthy and parasitised fruit fly larvae (Drosophila melanogaster) in Petri dishes that contained both regular food and food laced with alcohol. The alcohol content was comparable to that of beer.

Eighty per cent of the parasitised larvae favoured the boozy food, compared with just 30 per cent of healthy ones.

The parasites normally eat developing fruit flies from the inside out, but the experiment's open bar policy helped flies escape this fate. Parasitic wasps avoided depositing their eggs in booze-soaked fly larvae.

The alcohol appeared to keep the wasps at bay, say the researchers. For their young, the consequences of developing in a boozy environment are "gruesome", says Schlenke. "The wasps die and all of their organs are diverted out through their anus. Their guts actually pop out."

In addition to warding off parasites, the alcohol appeared to have a cleansing effect on flies that were already infected. Infected larvae that consumed alcohol were more likely to survive than teetotallers.

Entomologist May Berenbaum of the University of Illinois at Urbana-Champaign advises temperance for humans seeking alcohol as a cure for their ills. "We don't live in a sea of ethanol so it's kind of a different world for us," she explains. "We aren't nearly as good as metabolising it as fruit flies."

Journal reference: Current Biology, DOI: 10.1016/j.cub.2012.01.045

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