Attraction of female Aedes aegypti mosquitoes to 1-octen-3-ol (octenol), CO 2 , lactic acid, or ammonia emitted by vertebrate hosts is not only contingent on the presence of odor-ants in the environment, but is also influenced by the insect's physiological state. For anautogenous mosquito species, like A. aegypti, newly emerged adult females neither respond to host odors nor engage in blood-feeding; the bases for these behaviors are poorly understood. Here we investigated detection of two components of an attractant blend emitted by vertebrate hosts, octenol, and CO 2 , by female A. aegypti mosquitoes using electrophysiological, behavioral, and molecular approaches. An increase in sensitiv-ity of octenol olfactory receptor neurons (ORNs) was correlated with an increase in odorant receptor gene (Or) expression and octenol-mediated attractive behavior from day 1 to day 6 post-emergence. While the sensitivity of octenol ORNs was maintained through day 10, behavioral responses to octenol decreased as did the ability of females to discrimi-nate between octenol and octenol + CO 2 . Our results show differing age-related roles for the peripheral receptors for octenol and higher order neural processing in the behavior of female mosquitoes.