Killing off all the mosquitoes is pretty challenging. Mosquitoes have a short flight ranges, from 300ft to 3 miles. So whatever method you use has to cover every mile of land. They are attracted to CO2, which makes it difficult to make a trap that is any more effective at attracting them than every other person around. Bats can eat a lot of mosquitoes, but they also eat a lot of other insects too, which would have side-effects.