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Real Bar Flies Prefer Pale Ale

A new study was reported last week by NPR about research into why insects are drawn to beer. When I was a kid, I remember my Great Aunt placing beer in shallow bowls and laying them on the floor around her house to attract, and drown, pesky insects. I’d always assumed that was because of the sugars in beer and the fact that many, if not most, insects are drawn to sweet flavors.

So scientists in Southern California looked closer at this phenomenon and published their results in Nature Neuroscience. The article, inscrutably titled Evolutionary Differences in Food Preference Rely on Gr64e, a Receptor for Glycerol, finds insights “into the molecular mechanisms of feeding acceptance of yeast products and raise the possibility that Gr64e contributes to specific evolutionary variations in appetitive selectivity across Drosophila species.”

Happily, the NPR article, clears up what that means:

Since flies are well known to like sugar, it could just be that flies like beer because they can detect some residual sugar in beer. But [researcher Anupama] Dahanukar suspected that might not be the case. So she planned an experiment. She would give the flies a choice between beer and sugar water, and see which they preferred.

“We selected a pale ale, and the main reason was because pale ales have very lower sugar contents,” says Dahanukar. “So we were trying to identify other chemicals — chemicals other than sugars that taste good to flies.”

Zev Wisotsky, a graduate student in Dahanukar’s lab, actually performed the experiment. “I remember it was a Saturday,” he says. “I grabbed the beer at the grocery store, came into the lab, and performed the two-choice assay.”

The two-choice assay forces the flies to choose between a sip of beer and a sip of sugar water. The flies went for the beer.

Figure 1: Feeding preference to yeast fermentation products is reduced in Gr64e mutants.

(a) Feeding preference of wild-type flies (w1118) for beer (Bass & Co., Pale Ale) in a binary choice assay. For each concentration, n = 6. PI, preference index. (b) Feeding preference for beer, tested against 5 mM sucrose, in D. melanogaster…

Once they established the fly’s preference for beer, the scientists set about trying to figure out why.

“The answer, as it turns out, was quite simple,” says Dahanukar. “It’s a molecule called glycerol, which is made by yeast during fermentation.” Glycerol is the stuff that’s used in antifreeze. It actually tastes sweet, but it’s not a sugar.

Dahanukar and [researcher Zev] 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-beer choice, the flies went for the sugar water.

Apparently, the ultimate purpose of the research is to understand how insects perceive chemicals in the hopes of designing better insect repellents. But for my money, I love the fact that they love Pale Ale.

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