FWIW,
Some years ago I took a fly fishing guide out of Darwin and asked him the same question as I had been well and truly hammered by these little guys
He said the only thing that really works is baby oil, he said they basically drown in the stuff before they can bite
Made a 3 month trip to far nth Qld last year and did not have too much of a problem,
This is how I survived,
1- buy some "Itch Eze" from the chemist, I think it is a derivative of novocaine and works a treat on the occasional bite and stops the itching
2-Buy a couple bottles of baby oil, you will have to re-apply now and again
3-Buy a few cans of the Bushman heavy duty, (has lots of DEET), believe the DEET is not that good for you but it is the only product I find that works,
Spray often around the neck and cuff area, (this is where the oil soaks in and you get caught out
Lastly, like sun tan cream,
Re-apply often and before you enter that mangrove fish infested area, re-apply before you go in and then the occasional spray while you are there should do the trick
It does become a PITA having to re-apply this all the time but the alternative is much worse IMHO
Regards,
Gary