Repellent activity of nesting trees in the Sebitoli chimpanzee community of Kibale National Park, Uganda
Abstract
Every night, like all great apes, chimpanzees (Pan troglodytes) build a “nest” by intertwining stems and foliage. As nighttime is a key period when female mosquitoes are feeding and may transmit diseases, chimpanzees may have developed strategies to avoid biting at this time. Indeed, a previous survey showed that they use to build their nest at tree heigh where fewer female mosquitoes are present. As most of chimpanzees’ communities studied have a preference for trees in which they nest, a complementary strategy could be to choose species that emit aromatic substances to reduce bites risk. To test this hypothesis, we analyzed 1081 recorded nesting trees between 2017 and 2019 to determine the 10 most used trees and compared them to the 10 common trees yet not preferred for nesting in the Sebitoli community of Kibale National Park in Uganda. Extensive bibliographic research show that more biological properties were found in the leaves and bark of nesting trees. Interestingly, four nesting trees were reporting having potentially repellent/fumigant properties according to ethnological surveys. Then, we hydro-distillated leaves from the 20 trees selected to obtain essential oils for bioassays against females of the African mosquito, Anopheles gambiae. We discovered that out of the 10 nesting trees, 7 showed repellent activity, 7 were irritant (vs 3 and 5 respectively in common trees) and none were toxic. This study is one of the first evidence that chimpanzees could choose their nesting trees according to their biological and chemical properties, a potential inspiration for human health.