How to make people taste gross to insects

"The insects would sense an aversive chemical and be disinclined to take a bite," says Craig Montell. (Credit: iStockphoto)

Fruit flies have 68 receptors on their tongues that allow them to taste sugars and bitter compounds.

Scientists say they’ve identified a set of three receptors (called gustatory receptors or GRs) that allow flies to taste the noxious amino acid L-canavanine, which is found in plants such as clover and alfalfa.

The team also found that GRs in fruit flies (Drosophila melanogaster) that sense nasty compounds are cation channels, which means they have the ability to open and close in response to chemical or mechanical signals. These channels activate neurons by letting in positively charged molecules such as calcium or sodium.

fruit flies feeding
Mutant fruit flies feed on L-canavanine, a noxious amino acid. (Credit: UC Santa Barbara)

“Our finding that insect GRs collaborate to form a cation channel is of interest because it will set the stage for identifying safe and cheap chemicals that deter insects from biting,” says Craig Montell, a professor the University of California, Santa Barbara.

“Fruit flies avoid L-canavanine and now we know the identities of the set of receptors that activate a neural pathway that gives a stop-feeding signal,” he adds.

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According to Montell, the team’s discovery may one day be applied to disease-carrying pests such as mosquitoes. They describe the work in Nature Communications.

Because the GRs that provoke insect aversion to L-canavanine are cation channels, scientists will now be able to conduct high-throughput chemical screens to find equally aversive but safer and less expensive chemicals to use to prevent insects from biting people and spreading disease.

Some fruit fly GRs are conserved in insect pests, and in those cases they are likely to have similar functions in disease-carrying mosquitoes.

“Even if the related GRs in mosquitoes are fairly different, we now have the conceptual framework to demonstrate that their GRs are also ion channels,” Montell says. “We wouldn’t actually use Drosophila GRs to do chemical screens. We would use GRs in insect pests that we want to keep away.”

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Once an effective chemical target has been identified, scientists could use it to develop a secondary insect repellant. While it would not prevent insects from landing on skin, chemicals that activate GRs that ordinarily cause a stop-feeding signal could prevent mosquitoes from biting.

“The insects would sense an aversive chemical and be disinclined to take a bite,” Montell says. “Combined with insect repellants that interfere with olfactory attraction to humans, a GR-targeted repellant could offer a second line of defense.”

Source: UC Santa Barbara