Olfactory response of the antennal trichoid sensilla to chemical repellents in mosquitoes, Culex quinquefaciatus

Mosquitoes rely heavily on their olfactory system for host blood seeking, chemical detection, reproduction and survival. Odor chemicals are recognized by the mosquitoes’ olfactory receptor neurons (ORNs), housed at the base of hair-like sensilla on the antennae and maxillary palps. To gain insight into the mosquitoes’ response to chemicals, we investigated the interaction between the olfactory system of the mosquito Culex quinquefaciatus and chemicals with a repelling effect using single sensillum recordings from the trichoid sensilla on female antennae. A total of 50 repellent chemicals were used to examine their interaction with all six different types of trichoid sensilla including; long sharp trichoid, short sharp trichoid, blunt trichoid I, blunt trichoid II, short blunt trichoid-curved and grooved peg. The results showed distinctive response profiles of the sensilla to the chemicals. Chemicals which are important components of products for repelling mosquitoes, such as linalool, eucalyptol, alpha-pinene, and beta-pinene, had dose-dependent effect and displayed significant strong stimulation to the ORNs, while other chemicals showed no or weak effects on the ORNs. However, the mosquitoes showed no difference in response to isomers of the same chemicals, such as (-)-beta-pinene versus (+)-beta-pinene and (-)-menthone versus (+)-menthone. In addition, the mosquitoes took on response bias to terpene-derived chemical repellents compared to non-terpene-derived chemicals. Taken together, the study elucidates the effects of selected chemical repellents on the mosquito olfactory system and provides valuable information for screening new insect repellents and designing new mosquito control agents.