The research team first focused on its observation that silver vine leaves crumpled and torn by cat licking and chewing appeared to have a much stronger aromatic odor compared to intact leaves. They quantified the airborne emission and chemical profiles of iridoids that induce the feline response (such as nepetalactol, dihydronepetalactone, and isoiridomyrmecin) before and after feline licking and chewing. Physical damage of silver vine by cats promoted the immediate emission of total iridoids, which was 10-fold higher than from intact leaves. Leaf damage also changed the composition of iridoids in silver vine. Nepetalactol accounts for over 90% of total iridoids in intact leaves, but this drops to about 45% in damaged leaves as other iridoids greatly increase. To examine whether these changes in iridoids when silver vine leaves are damaged influence the feline response, the research team prepared synthetic iridoid cocktails corresponding to the ratios found in intact versus damaged leaves, and presented these simultaneously to a set of cats. The altered iridoid mixture corresponding to damaged leaves promoted a much more prolonged response. “It was easy to speculate that the response duration would increase with the amount of iridoid. However, it was surprising that the change in iridoid composition when silver vine leaves were crumpled and torn by cats also greatly increased the cats’ response. The increased emission of iridoids from damaged leaves and changed chemical composition add together to induce a more extended duration of rubbing and rolling response, allowing cats to transfer more mosquito repellents to their fur. This helps to reduce the health risks and irritation associated with mosquitoes. We can say that licking and chewing these plant leaves also contributes to chemical pest defense in cats”, said Professor Masao Miyazaki of Iwate University, a leader of the research project.
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