DEET was used as an effective repellant* until a couple of years ago, MMcC maybe you're thinking of DDT?!
(edited) * for use on humans, it is still available in products like "Naff Off" https://www.amazon.co.uk/Deet-Power-Repellent-Spray-750ml/dp/B004W2B1J6?ie=UTF8&*Version*=1&*entries*=0
I still use a DEET spray when mowing the lawn to keep those horseflies from ripping chunks out of my 6 pack (ha ha if only).