I think all borders are porous to mosquitos.
DDT
Now
Sadly, tiger mosquitoes (invasive species from Asia) have been spreading over the US, so all we need are some immigrants with dengue to start the spread here.
Dengue is one nasty disease and can have nasty after effects, too. Close friend of mine had it in SE Asia, and I was grateful I just got malaria. Yes, I’d much rather get malaria than dengue.