How exactly do mosquitoes navigate directly on target?
Mosquitoes do not rely on a single cue to find its host. It is the combination of CO2, temperature and odor cues, that makes mosquito an efficient blood feeder.
 These two papers might help you in understanding how mosquitoes target their hosts.

Genetic analysis of mosquito detection of humans

Multimodal Integration of Carbon Dioxide and Other Sensory
Cues Drives Mosquito Attraction to Humans