'Fruit flies booze heavily to kill off parasites'

It appears that fruit flies can out-drink heavy boozers and not even fall sick, as scientists have found these insects get drunk to kill off wasp parasites in their bloodstream.

A team at the Emory University in Atlanta found fruit fly larvae not only feed on the yeast and other fungi from rotting or fermenting fruit, but also ingest the boozy byproducts that have up to four per cent alcohol.

But, strangely, the drunk fruit-fly larvae thrive on the food and use the alcohol to kill off wasp parasites in their bloodstream, essentially causing the parasite's organs to drain from its anus, the researchers found.

Todd Schlenke, an assistant professor at Emory who led the study, said higher alcohol levels can be toxic to the fruit flies. "If the alcohol level gets too high, they can't break it down fast enough," Schlenke told LiveScience.

The flies in the study only reached about 0.02 per cent blood alcohol levels, they would have to drink four times that to reach the level considered illegal for driving. This idyllic existence on a booze-soaked piece of fruit is often disrupted by parasites, including wasps that lay their larvae in the larva of the fruit fly.

If untreated, the tiny wasps eat the flies from the inside out, bursting from the flies bloodstream fully formed. But, the flies use their naturally high tolerance to alcohol to kill off their blood bugs, the researchers discovered.

In the study, published in the journal Current Biology, when the wasps tried to lay their eggs in fly larvae on food containing six per cent alcohol, they  were less likely to lay eggs, "presumably because they are feeling bad," Schlenke said, and the eggs they did lay were less likely to survive.

"If you dissect open a fly that was fed alcohol food, the wasps were obviously dead and in a lot of cases the internal organs in the wasp larvae had fallen out the wasp's anus," Schlenke said.

The researchers also found that when infected larvae were placed in a dish with both alcoholic and non-alcoholic food, they even made a break for the alcohol to reduce their parasite load: After 24 hours, 80 per cent of the infected fly larvae were hanging out on the alcohol side of the dish.

"We gave them a choice between food with alcohol and food without alcohol, and the infected flies overwhelmingly went to consume the toxic alcohol food," Schlenke said. It's as if the flies ask themselves, "Do I want to suffer from toxic levels of alcohol or do I want to die from this wasp?"