they reproduce too damn fast, and with their rapid lifecycle comes the development of resistant strains.
Now, what we do know (I learned this in junior school!) is that mosquitoes breed in stagnant water.
How about a mechanical control method, that's been proven to work? DRAIN THE POOLS, PUDDLES, OPEN SEWERS, AND ANY OTHER BODY OF WATER WHICH DOESN'T FLOW! Problem SOLVED!
(Fuck Monsanto et al whose business depends on shifting ludicrous amounts of the nastiest chemicals known to exist).