Most people at some point could use a drink — after a long day at work, during a harrowing misadventure, while arguing with people on the Internet — but what if it were a matter of life and death?
For the common fruit fly, it sometimes is. As its name implies, the Drosophilia feeds on fruit. Sometimes, the fruit will fall from the branch and ferment, bringing its alcohol content up to around 20 percent. This is usually somewhat toxic to flies, but in the presence of wasps, which lay eggs on the fly larvae and pupae (flies go through stages similar to a butterfly's), the flies are more likely to lay eggs on fermented fruit, Ars Technica reports.
The reason for this is that even small amounts of alcohol are toxic to parasitic wasps, and while some larvae will die from the exposure, many others will survive. The maggots have no other options — they eat whatever the mother decides to lay them on, and when offered the choice in the absence of wasps, the flies consistently chose fruit untainted by booze, which would allow their offspring to thrive more easily.
When wasps — specifically female wasps, because the males are not direct threats to the maggots — are present, the flies form a long-term memory that will induce them to continue laying eggs on alcohol-laced fruit, even days after the wasps are removed. They also learned to recognize and identify different species of wasps, which suggested to the study's authors that the species-identification and alcohol tolerance may have evolved altogether. Species of flies with no tolerance would not lay eggs on alcoholic fruit regardless of the presence of wasps.
The flies would lay eggs on the alcoholic fruit up to a concentration of about 16 percent (32 proof is their limit, it seems), approximately the same amount found in naturally fermented fruit.
The study, Fruit Flies Medicate Offspring After Seeing Parasites, was published in Science Magazine on Friday, Feb. 15.
