The FDA does no testing of its own but rather relies on the manufacturer to supply testing data. What could go wrong?

Actually DDT is safe. The problem was two fold-
The like known as Silent Spring.

Using too much DDT at one time.

Seems I remember something like that

Yes, what happened was the DDT travelled up the food chain until they reached the bald eagle, which caused the shells of their eggs to be abnormally thin and usually die

https://junkscience.com/1999/07/100-things-you-should-know-about-ddt/#ref6