Fruit Flies Get Their Babies Drunk To Kill Off Parasites

Fruit flies may seem like pests to us, but they have parasites of their own. A tiny wasp known as Leptopilina heterotoma, infects their larvae (a life-stage right after birth) and will devour and kill them.

Interestingly, fruit flies have ways to avoid this wasp: They change their behavior.

New research, which will be published in the journal Science on Friday, Feb. 22, showed that when female fruit flies see the wasps, they are more likely to lay their eggs in food that contains alcohol.

The parasitic wasps like to lay their eggs inside the fruit fly larvae. The eggs grow inside the larvae, eventually consuming and killing them — bad news for the mommy-to-be.

Because the flies feed on the yeast that live on decomposing fruit, they have a high tolerance for booze, which the yeast makes as a byproduct. Compared to the flies, the parasitic wasps don't handle their booze well.

Previous studies have shown that when fruit flies are infected with these parasites, they get wasted by eating foods high in alcohol to kill them off. The baby wasps can't survive as high levels of alcohol as the fly can, and they die.

In the new study, Balint Kacsoh and colleagues at Emory University found that when parasitic wasps are nearby, female fruit flies lay their larvae in alcohol-infused environments. (Usually they prefer alcohol-free environments, because in high concentrations booze can be toxic to the insects). When infected larvae are grown in alcohol, the parasites can't survive.

They only laid their larvae in alcoholic substances when the wasp nearby was specifically threatening to the life-stage of their offspring. They didn't lay their larvae in alcohol when the wasp nearby was either male or immature because those are not a threat to the offspring.

The researchers found that one single molecule — called neuropeptide F — controls whether the female fruit fly lays her larvae in an alcoholic or non-alcoholic substance.