The exact mechanism is not completely understood, but it's thought that DEET works because it interfere's with mosquitos ability to locate their prey. It is not thought to discourage bites as "they don't like the taste", just by interfering with sensing.

A newer repellent, Picaridin, not only interferes with locating prey, but actively deters mosquitos like pepper spray mace. It's an engineered molecule, derived from a compound called piperine, a substance found in black pepper plants.

Studies show that "Picaridin is as effective as DEET", but my personal experience is it is about twice as effective as DEET.

I spend an enormous amount of my free time outdoors and I can attest that Picaridin is far more effective than DEET for both mosquitos and ticks (we have two main species in the Kansas/Missouri/Arkansas region, others are present but less common).

As a personal data point, I had a friend trip on a hike this spring and fall into a grassy/bushy area. He did not put any repellent on. When we stood up, he was _covered_ in ticks. We got back to the truck and started peeling them off him, probably 15+ plus we flicked off or crushed. Unfortunately, we kept finding more, so we tried spraying Picaridin after the damn things hated that stuff so bad they jumped or fell off instantly.

You do not want to get Picaridin in your eyes or mouth, holy shit, that stuff is like bear mace. Also make sure you're downwind when you're spraying, your friends with appreciate that.

The other advantage of Picaridin is that it does not melt certain plastics. If you have life saving gear made of certain plastics, DEET can melt many times of plastics! (Notably some PVCs, polycarbonates, acrylics, acetates, and elastics).

But if what they wanted to achieve was to show how to make DEET ineffective then I hope their entire research department is proscribed as the terrorist organisation it really is by every nation on Earth.

The simple answer would be to add a natural strongly repellent gentle oil to the DEET spray.