I have posted this somewhere else (under sleeping bags, or something similarly misleading), but this week I found a product in a pharmacy - as yet untested, that claims to treat clothing and other fabric for up to 2 weeks - killing biting insects on contact.
It is Bugproof Clothing Treatment from Nomad Medical 3-4 Wellington Terrace, Turnpike Lane, London N8 0PX. No telephone or website listed on the pack, alas. I bought it in an independent pharmacy in Weymouth, but presumably the company would be able to give you a supplier near you. It cost £5 for 100mL (actually, I get a discount in pharmacies, courtesy of being a community nurse, so it may be slightly more), which is enough to treat a shirt, pair of trousers and socks. I aim to treat my (home made) silk sleeping bag. It contains permethrim, for those that worry about these things (it is also used to treat head lice, scabies and crab lice...).
I am all for the power of the mind, and the advantages of positive thinking, but also like to lay my head down at night without the lurking suspicion that the less endearing arthropods of the class Insecta are after my blood.
Let your Camino be bugless!