This thread started out when I posted a humorous story about dealing with no-see-ums for the entertainment of members of the forum, but has evolved into a general discussion of how to repel bugs. So here's something which currently isn't a problem in Canada and adjacent areas: Leishmaniasis (Google it, and be prepared to see some truly hideous photographs). This is a flesh-eating parasite in tropical areas of South and Central American which is spread by the bites of sand flies, which are little bugs a fraction the size of mosquitoes. Tyler Bradt, an internationally known whitewater kayaker (Google him) who holds the world record for kayaking down the highest waterfall (Palouse Falls in Washington, 186 feet, Google it), was on a kayak trip on the Amazon when he got chomped by some of those sandflies. Shown below is a picture of him after two months, with an advanced stage of mucosal Leishmaniasis in his lip, nasal passages, throat, and right eye. About a week later the US Center for Disease Control diagnosed the variety of the Leishmaniasis parasites, and he is currently undergoing a thirty day treatment which is very similar to chemotherapy here in Missoula. I hope it works; this is a nasty disease.

So in some situations, I think forget about the repellants. Leave no skin exposed. Wear a bug shirt, bug pants, gloves, etc.