Fruit flies get drunk to improve survival

Quick, what does the everyday fruit fly have in common with a week-weary Hopkins student on a Saturday night? It might seem odd, but both are probably looking for a tasty drink of alcohol for a bit of a boost.
As much as this sounds like a poorly constructed joke, researchers from Emory University's Department of Biology actually looked into the role that alcohol consumption plays in protecting Drosophila melanogaster, the common fruit fly, from one of its natural enemies, the endoparasitoid wasp. As their name implies, endoparasitoids lay their eggs inside a host species, allowing the parasitic egg to feed off of the host and ultimately kill it.
Fruit fly larva have been known to mount a defense called encapsulation against two types of wasps - the Leptopilina boulardi species, which specializes in infecting fruit fly larva, and the Leptopilina heterotoma species, which is a general endoparasitoid.
When the larva detects an infection, it begins a process in which it wraps the parasite in layers of tissue, forming a capsule and immobilizing and killing the target.
However, in a recent study published in the journal Current Biology, the research team from Emory, led by Assistant Professor Todd Schlenke, realized the potential for a new defense mechanism for fruit fly larva based on their eating habits.
Fruit flies often eat from rotting fruit which contains about four percent ethanol by volume due to fermentation. As a result, D. melanogaster has evolved a slight resistance to ethanol to combat its potentially poisonous effects. This adaptation allows fruit flies to reach blood alcohol levels of up to 0.02 percent, which is a fourth of the minimum amount of alcohol considered illegal for driving. Wasps, on the other hand, have no such diet and are
See FLIES, page B8
FLIES, from B7
therefore susceptible to alcohol poisoning.
From these two facts, researchers hypothesized that perhaps ethanol content in fruit flies could offer some protection to fly larva against wasp infection. Milan and his team went about testing their hypothesis with a variety of different experiments, each looking at different aspects of how ethanol consumption could alter fruit fly resistance.
The group began by setting up two types of food mediums, one with 6% ethanol content by volume and another normal food medium without any ethanol. They then went on to compare D. melanogaster larval infection rates, larval survival, L. heterotoma and L. boulardi parasite survival, and larval movement when fed on the two different mediums.
The results were astounding. In every category, the data revealed that ethanol has a major impact on the larva-wasp interaction. 'Drunken' fruit fly larvae were less likely to be infected and more likely to survive infection, while the wasp parasites living in these inebriated hosts fared far worse.
In an interview with Live Science, Schlenke explained how wasp parasites were essentially "turned inside out" by larva that had been fed on the ethanol-containing medium.
Perhaps the most intriguing result the Emory group came across occurred when they placed infected D. melanogaster larva on petri dishes half-filled with ethanol medium and half with normal medium.
Researchers observed the larva moving back and forth between the two mediums. But instead of a drunken amble, the larva were apparently finding a balance between consuming enough ethanol to fight off the parasitic wasps while not consuming enough to cause alcohol poisoning.
While connecting fly diet with wasp infection seems farfetched, the researchers were able to prove that ethanol truly does protect fly larva from potential wasp infection.