Hi Jean-Marc,
A few thoughts on the matters of BABs (Bad-Assed Bugs):
1) Clothing: +1 for George's suggestions. If you don't want to spring for mozzie-mesh shirt & longs, then just make sure that your long-sleeved shirts are closed at the wrist & neck, and your long pants ditto at the ankles. For a bug veil, I find the best ones are long, so that they cane drape over your shoulders. Failing that, make sure that any drawstring goes outside your collar.
2) Repellents: People have different bio-chemistries, so what works for one person may not work for another. E.g.: friends have recommended Skin-So-Soft, but it doesn't work at all for me. Ditto for citronella.
The only manufactured chemical repellent I've found that works is DEET, and the higher concentration, the better. (95% is the max I've seen.) BUT: I
don't put this on my skin, just on my clothing at key points of entry. And beware--it can dissolve nylon, so keep it away from nylon clothing, tents, etc. OTOH, it's an excellent fire-starter.
I have used one repellent made from natural ingredients such as eucalyptus. This came from a recipe said to by used by indigenous people, and sold by a friend of our daughter. Her company has the splendid name of Aroma Borealis, and it's based in Whitehorse, Yukon, where they know a thing or two about bugs. But, that's a long way from where you are, and last I checked, Bev didn't sell the repellent (called "Skeet-addle" -- they know a thing or two about word play in Yukon, too) any more.
3) On midges: We have them here in Eastern Ontario, in the spring, but they're not too serious, more of a nuisance. Ten years ago (!!) I spent a week hiking the West Highland Way in mid-June, and the midges weren't bad. I camped a couple of nights, and found that my hat + bug veil was enough. OTOH, where there was a carpet of heather (where midges are s'posed to swarm in their jillions), on Rannoch Moor, I didn't have a quiet still evening--there was a fierce wind-and-rainstorm, and the midges took cover.
4) Traditional bug repellents: The workers who built Canada's railways in the 19th century, and who maintained them during the 20th, used something called a smudge pot: a heavy pail carries a layer of moss, some lighted charcoal, and more moss. This generates thick acrid smoke which keeps everything away, including blackflies (see below.) Not very handy for a cyclist, though. (Don't confuse a smudge pot with a smudging ceremony, though--that's something else again.)
5) The blackfly: Nothing works to keep these savage brutes away, 'cept for the smudge pot. You don't have to worry about these in old Scotland, however -- but you do have to worry about them in Nova Scotia & points west.
How bad are they? Here is Wade Hemsworth's song and the animated comic:
https://www.youtube.com/watch?v=qjLBXb1kgMoCheers, John