Yong Huang wrote:
Here in Houston sometimes around midnight, the City dispatches a truck
to spray some chemical in neighborhood. The next day, there're less
mosquitos. What is that chemical? Can we buy it from any store? Some
parks in the city have absolutely no mosquitos. I think they treated
the grass and tress with some magical stuff too.

Yong Huang

Problem is - as you have seen - they have to KEEP spraying it.

If you use DDT (hard to get, but possible), it's with you forever.