How one of the oldest natural insecticides keeps mosquitoes away. Duke Today, May 11, 2021. A new study has identified a scent receptor in mosquitoes that helps them sniff out and avoid trace amounts of pyrethrum, a plant extract used for centuries to repel insect pests. These findings could help researchers develop new broad spectrum repellents to keep a variety of mosquito species at bay, and by extension stop them from biting people and spreading disease. Picked up by Scientific American and WRAL-TV.