Scent of a fruit fly larva comes from its gut microbes

Fruit fly larvae’s alluring and socially important odor turns out not to come from the flies at all, but from their gut microbes.

Scent is a big deal to Drosophila melanogaster fruit flies. Both adults and larvae tend to shun untouched food in favor of clustering where larvae have already fed, researchers at McMaster University in Hamilton, Canada, reported last year. The insects find such food by the larvae’s scent.

Now McMaster researchers have found that fruit flies outsource this bit of attraction chemistry to the microbes in their guts, Reuven Dukas and colleagues report April 16 in the Journal of Experimental Biology.

In one of a series of lab tests, the researchers found that larvae without gut bacteria didn’t leave attractive traces. Adding either of two Lactobacillus gut microbe species to the larvae restored some of their appeal.

The scent reminds coauthor Zachary Durisko of “leftover autumn leaves after the first long spring rain has melted the snow. It’s rotting,” he says, “but it’s not horrible.”