Fruit Flies Feed their Children Alcohol: Good Parenting Advice for Insects

Feeding alcohol to children may seem like the worst parenting advice in history, but for fruit flies it could help their offspring survive. Researchers found that when fruit flies sense parasitic wasps in their environment, they lay their eggs in an alcohol soaked location, forcing their larvae to consume the booze as a drug to combat the dangerous wasps.

The findings, published in the journal Science, examined whether or not fruit fly parents could sense when their children were at risk for infection, and whether they then sought out alcohol in order to medicate them.

Since the larvae of the common fruit fly eat the rot, or fungi and bacteria that grow on overripe, fermenting fruit, they've evolved some resistance to the toxic effects of alcohol levels in their natural habitat. These levels can range up to 15 percent.  

These fruit flies, though, don't have it easy. Tiny, endoparasitoid wasps often inject their eggs inside fruit fly larvae, along with venom that can suppress the hosts' immune response. If the flies fail to kill the wasp egg, it hatches and then eats its host from the inside out.

In order to test their latest query, scientists released adult female fruit flies into a two different mesh cages. One had parasitic wasps inside while the other had no wasps. Both of the cages had two petri dishes containing yeast, which is used in the lab for raising fruit flies and their larvae. While one petri dish had yeast that was mixed with six percent alcohol, the other dish of yeast was alcohol free. After 24 hours, the petri dishes were removed and the researchers counted the eggs that the fruit flies had laid.

Overall, they found that 90 percent of the eggs in the cage with parasitic wasps were laid in the alcoholic yeast. In the cage with no wasps, though, only 40 percent of the eggs were laid in the alcoholic yeast. Clearly, the fruit flies changed their behavior patterns depending on whether or not there was a threat of infection by the parasitic wasps.

The researchers didn't stop there, though. Further experimentation showed that the fruit flies preferred the alcoholic yeast more when female wasps were present, but not if only male wasps were in the cage. The scientists then tested to see if the flies were either smelling wasp pheromones or merely looking at the wasps to make the distinction. They used blind flies and flies that could not smell in their experiment. Surprisingly, the blind flies did not choose the alcoholic yeast, whereas the flies unable to smell did. This finding points to the fact that the fruit flies used visual cues to note the presence of the wasps.

"Medication may be far more common in nature than we previously thought," said Todd Schlenke, whose lab did the research, in a press release. "We found that this medicating behavior was shared by diverse fly species, adding to the evidence that using toxins in the environment to medicate offspring may be common across the animal kingdom."