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Climate Change

Catnip makes mosquitoes feel pain

The same compound that attracts kitties activates pain receptors in mosquitoes

by Laura Howes
March 4, 2021 | A version of this story appeared in Volume 99, Issue 8

A close-up of a catnip plant on a white background.
Credit: Shutterstock
Cats might go crazy for catnip, but for mosquitoes it causes pain.

Watch a cat intoxicated by a sprig of catnip, and you’ll see the plant’s iridoid compounds at work activating feline opioid receptors. But these compounds have a completely different effect on mosquitoes and many other insects: they drive the pests away. Now we know why. Researchers have found that the compounds that cause such pleasure in cats cause pain in mosquitoes (Curr. Biol. 2021, DOI: 10.1016/j.cub.2021.02.010).

It’s not news that catnip repels mosquitoes. Various historical references describe using the plant, which is a relative of mint, to repel bothersome bugs, and in the 1960s, Thomas Eisner of Cornell University chased insects around with catnip oil to prove it worked (Science 1964, DOI: 10.1126/science.146.3649.1318).

The structure of cis,trans-nepetalactone, a cyclic terpene.

But Marcus Stensmyr of Lund University and colleagues wanted to understand the mechanism of this repellence. The researchers found that in mosquitoes, catnip extract and the key compound within, cis,trans-nepetalactone, activate a receptor­—the transient receptor potential ankyrin 1 (TRPA1) ion channel—that senses environmental irritants like pain and itch. Mutant mosquitoes that lacked TRPA1 remained unfazed by catnip or its oil, the team found.

Most animals, including humans, carry this receptor, and in both humans and mosquitoes, plants like wasabi trigger it. But the new work shows that the receptors differ in their responses to catnip compounds: humans’ receptors aren’t activated by catnip compounds, but the receptors in mosquitoes fire. These findings mean that iridoid compounds could be an excellent starting point for developing low-cost insect repellents, researchers say.

Laura Duvall, who works on mosquito behavior at Columbia University, says that researchers traditionally thought that a lot of these repellents hit taste and smell pathways in mosquitoes. Finding that the compounds, which work only at close range, cause pain “is something a little bit different.”

“The fact of the matter is we really don’t know why the plants might make these compounds,” says chemical ecologist Sarah O’Connor of the Max Planck Institute for Chemical Ecology, who was not involved in the research. But she says the work is “a great piece of evidence” suggesting that the plants use the compounds to protect themselves from insect pests.

Using natural compounds found in plants is an attractive way of controlling insects, Stensmyr says, because in some settings these plants are cheaper and easier to obtain than common synthetic insect repellents like N,N-diethyl-m-toluamide (DEET).

DEET is still the gold standard, but the researchers say that uncovering how catnip iridoids react with mosquito TRPA1 could help scientists design more potent and selective insect repellents in the future.



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