I would like to know the mode of action of mosquito repellent aerosols. Are these specific to mosquito or are other insects affected too?
The most common active ingredient in insect repellents is N,N-diethyl-3-methylbenzamide (other name: N,N-diethyl-m-toluamide; abbreviated DEET). It provides protection against mosquitoes and many other insects. After various interesting hypotheses, it is currently assumed that mosquitoes simply smell DEET directly and avoid it.
Citronella oil is also used as an insect repellent and is seems effective on mosquitoes and head lice as well. Though I was not able to find information on the mode of action, just the effectiveness of citronella.
Wikipedia also says DEET is effective for fleas, ticks, and chiggers (though this lacks a references). Anecdotally, I know the Off brand of repellent is useful when the dogs get fleas to avoid getting all bitten up (Off contains DEET I believe).