What are the trade-offs of using insecticides to kill mosquitoes?

This can select for resistant mosquitoes. After a couple of years, the population is entirely resistant to the insecticides you used. The insecticides may also kill off the beneficial insects (like pollinators e.g. bees) or the predator insects that ate the mosquitoes. Bioaccumulation and biomagnification in the food chain can lead to unintended deaths of high-level predators, e.g. DDT leading to deaths of eagles and falcons. I hope this is correct. 

Genetic engineering is the answer.

The right answer is b hydrogen bonds!