Beer Or Sugar Water? For Flies, The Choice Is Pale Ale

Flies are attracted to glycerol, a chemical in beer produced during fermentation. Understanding more about the genes responsible for taste and smell in flies could help make powerful insect repellents.

Part I  

Part II 

LINDA WERTHEIMER, HOST: There are certain scientific studies that call out to NPR science correspondent Joe Palca, because they reveal something fundamental about the natural world. For example, a recent study from scientists at the University of California in Riverside reveals why fruit flies like the taste of beer. Surely that's a fundamental fact of nature. Here's Joe.

JOE PALCA, BYLINE: I've drunk my share of beer, but I have to admit I was surprised to learn that fruit flies like beer. Apparently I shouldn't have been.

ANUPAMA DAHANUKAR: The attraction of flies to beer was first reported in the early 1920s.

PALCA: That's Anupama Dahanukar. She's not in the school of bartending science at the University of California Riverside. There isn't one. No, she's part of an inter-disciplinary program involving neuroscience and entomology.

DAHANUKAR: We're interested in how flies recognize chemicals.

PALCA: So answering the question of why flies like beer is actually quite relevant to her research. It's not a simple question. Scientists are only just beginning to understand the basics of smell and taste in humans. So research on flies has been extremely helpful with that.

Now, as everyone, including me, knows, flies like sugar. So it could just be that flies like beer because they can detect some residual sugar in the beer. But Dahanukar suspected that might not be the case, so she planned a beery experiment. She would give the flies a choice between beer and sugar water and see which they preferred.

DAHANUKAR: We selected a pale ale, and the main reason was because pale ales have very lower sugar content. And so we were trying to identify other chemicals, chemicals other than sugars, that taste good to flies.

PALCA: It would be a thrilling, dare I say unforgettable, moment in science to prove that it was something other than sugar that attracted flies to beer.

ZEV WISOTSKY: I remember, it was a Saturday.

PALCA: Carrying out the experiment fell to graduate student Zev Wisotsky.

WISOTSKY: I grabbed the beer at the grocery store, came into lab, and performed the two-choice assay.

PALCA: The two-choice assay is where the flies get to choose between a sip of beer and a sip of sugar water.

WISOTSKY: They surprisingly went for the beer.

PALCA: Now that that was established, Wisotsky and Dahanukar went about trying to figure out which compound in the beer was attracting the flies.

DAHANUKAR: And the answer, as it turns out, was quite simple. It's a molecule called glycerol, which is made by yeast during fermentation.

PALCA: Glycerol is the stuff that's used in antifreeze. It actually tastes sweet, but it's not a sugar. Dahanukar and Wisotsky even found the particular gene responsible for flies' ability to detect glycerol. When they created flies missing that gene and gave them the sugar water or beer choice, they went for the sugar water.

The research appears in the journal, Nature Neuroscience.

There are practical applications that may result from understanding how insects taste and smell. For example, other scientists are developing powerful insect repellents based on what they've learned about insects' preference in the odor arena. You see, learning why flies like beer is both fundamental and practical.

Joe Palca, NPR News, Washington.

STEVE INSKEEP, HOST: Did he say the odor arena? Yes, he did. From flies drinking beer to good old fashioned bar flies. While most Americans were celebrating Thanksgiving, in Paris some were celebrating the 100th anniversary of a legendary watering hole.

Harry's Bar, originally called the New York Bar, opened on Thanksgiving Day in 1911. Its American founder wanted it to be a slice of Manhattan, so much so that he had a New York saloon dismantled and shipped to the City of Lights.

In the '20s, Harry's Bar was a favorite of expatriates like F. Scott Fitzgerald and Gertrude Stein. Many years later, Clint Eastwood would visit. The bar remains a favorite of expats and Parisians alike and is likely to stay that way as it enters a second century.

This is NPR News.