Seen your cat rolling around in catnip (Nepeta cataria) or silver vine (Actinidia polygama)? Your furry friend might be using it as an insect repellent.
Silver vine is a catnip alternative that cats love. Now, a team led by Reiko Uenoyama of Iwate University, Japan has found that this might be because of a specific chemical called nepetalactol.
Not only this, but the nepetalactol seems to repel mosquitoes after a cat has rubbed its face in it, according to their paper, published in Science Advances.
“The first appearance of silver vine (matatabi in Japanese) as a cat attractant in literature in Japan dates back to more than 300 years ago,” says researcher Masao Miyazaki.
“A folklore Ukiyo-e drawn in 1859 shows a group of mice trying to tempt some cats with a smell of silver vine. Still, benefits of the cats’ response had remained unknown.”
The team isolated substances from silver vine extracts and offered them individually to some test cats. The study group included lab cats, feral cats, jaguars, lynxes and a leopard. The cats all loved the nepetalactol the most.
“We applied nepetalactol to laboratory paper filters and tested with 18 laboratory and 17 feral cats,” says Uenoyama. “They displayed the typical response to silver vine. We also tested the substance with larger, non-domestic cats. They showed a similar reaction.
“We concluded nepetalactol is responsible for the typical feline reaction to silver vine.”
Dogs didn’t react at all.
To understand why their study subjects were so happy, the researchers tested whether cats were experiencing a similar euphoria to humans’ when our opioid system is stimulated.
“We tested β-endorphin levels before and after nepetalactol-induced response in cat blood,” says Miyazaki. “We found that silver vine activates the nervous system that is responsible for the euphorigenic reaction.”
So, do cats just like silver vine because it makes them happy, or is there another reason?
“On the basis of some reports that nepetalactone, the feline attractant in catnip, has mosquito repellent activity, we thought that the response allows cats to transfer plant’s nepetalactol or nepetalactone on their fur for protection against mosquitoes,” says Uenoyama.
“This led to a strong hypothesis when we found the mosquito repellent activity of nepetalactol.”
To confirm their hypothesis, they tested whether nepetalactol was actually being transferred to the cats. They found that the cats rubbed their faces on the nepetalactol-soaked paper, and the substance clung to their face and heads.
This appeared to act as a mozzie repellent for the cats, as less mosquitoes landed on the heads of cats that had nepetalactol applications.
“From these results, we found that the cats’ reaction to silver vine is chemical defence against mosquitoes, and perhaps against viruses and parasitic insects,” says Miyazaki. “This was the most significant finding of our study.”
But the question of whether other animals use this kind of defence remains.
“Why is this reaction limited to cats?” asks Miyazaki. “Why don’t non-feline animals react to the plant?”
“To find answers, we want to identify the gene responsible for the reaction. The findings of this study may be used in various applications, including development of new mosquito repellent products.”
Dr Deborah Devis is a science journalist at The Royal Institution of Australia.
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