Catnips – especially catnip (Nepeta cataria) and the Silver Vine (Actinidia polygama) – are known to induce felines to adopt euphoric behavior. The team of Pr Masao Miyazaki, from the University of Iwate (Japan), has been interested for several years in their effects. She now explains, in a new study published on June 14, 2022 in the journal iSciencewhy domestic cats often chew these herbs.
Repellent molecules hidden in the leaves of catnip
Faced with insects, plants develop defense mechanisms. A repellent effect that mammals – including humans – have been able to exploit by applying leaves to their bodies, for example. A previous study published at the beginning of 2021 by Masao Miyazaki, Reiko Uenoyama and their colleagues, had established that catnip can have a repellent action on mosquitoes thanks to particular molecules produced by the leaves, and called iridoids. Catnip produces an iridoid called nepetalactone while silver vine produces a more complex mixture of nepetalactol, dihydronepetalactone, isodihydronepetalactone, iridomyrmecin and isoiridomyrmecin.
“domestic cats (Felis silvestris catus) show an unusual but characteristic response to catnip (Nepeta cataria) and silver vine leaves (Actinidia polygama) which involves licking and chewing the plants, rubbing the face and head against the plants, and rolling over the plants“, recall the Japanese biologists in their new study. It is by rubbing on plants that they transfer iridoids to their fur in order to protect themselves from bites. But why do they chew them?
An increased release of molecules
The hypothesis of a real consumption of plants was quickly swept away. “Although licking and chewing plants promotes plant ingestion and digestion in most animals, our preliminary studies have shown that cats swallow minimal, if any, plant material.“, note the researchers. They finally discovered that by damaging the leaves of catnip and silver vine, cats increase the release of iridoids by them. The felines then rub themselves longer on the plants, which promotes their repellent action on hair.
The action on the leaves is however variable between the two plants. Thus, in catnip, the release of nepetalactone from damaged leaves increases enormously. In silver vine, wrinkled leaves do not produce the same “cocktail” of iridoids as undamaged ones. It is then very effective against mosquitoes, even at low concentrations.
Graphical summary of the study. “Silver vine” stands for silver vine and “catnip” for catnip. Credit: Masao Miyazaki & all / iScience
To protect themselves from mosquitoes, cats therefore not only rub against these plants. They chew them too. A behavior long equated with gambling, which could ultimately put biologists on the path to new plant enzymes capable of producing useful plant iridoids against a wide range of crop pests.