These people are just trying to sell fear. They don't have to deploy them, screwworms have been here for years. Ask any cattle farmer or deer hunter at least in the Southeast. They were in the Southwest before they came here. "Screwworms spread to the Southeast when producers unknowingly transported infested livestock there in 1933." The eradication programs in the late 1950's pretty much cleaned them out. I've found an occasional screwworm infected deer over the years but nothing to signal a widespread infestation. If they do become a problem we already know how to eradicate them.