um. My uncle died of polio, and I was a medical researcher (phd) for a while.

Polio can cause paralysis just fine on its own, it doesn't need DDT or paraquat to help it.

And you are also right that widespread spraying of DDT lead to all kind of problems (killed all the birds, for one, leading to "Silent Spring"), which one reason it was banned.

another reason is the mosquitos developed resistance.