11:44 a.m. on April 21, 2009 (EDT)
Having spent time in Alaska (mosquitoes there have crossbred with B29s, but carry no diseases), Mississippi (mosquitoes there carry equine encephalitis, a nasty way to die), New England (black flies, noseeums, mosquitoes, but they don't carry diseases), the Sierra (no diseases, but the small mosquitoes are overwhelming in number and like to land in food and drink just before you put them in your mouth), California lowlands (mosquitoes carry various diseases like West Nile virus, plus we have ticks with Lyme disease), and Africa (various insects, including mosquitoes, that carry everything from malaria and yellow fever to all sorts of other incredibly painful and deadly diseases), I have experimented with all sorts of things.
For me, I find that "natural" repellents (and SkinSoSoft) keep the beasts at bay for no more than 30 seconds. Most DEET products last about 10 minutes, with 100% DEET lasting 30 minutes (regardless of what the claims are). But the time-release forms of DEET (Ultrathon, Sawyers, a few others) work for 6 to 8 hours (the containers and ads claim "up to 12 hours", but much shorter for me). Soaking clothes in permethrin works well, but still leaves skin exposed, so the time-release DEET goes there. For Africa, we got Ex-Officio's BuzzOff shirts (here is a photo of us at the hippo pool from my Africa report here on Trailspace, wearing the BuzzOff shirts)
There is a fairly new product, picaridin, which is registered with the EPA , and is supposed to be nearly as effective as 100% DEET without most of the problems (I have no experience with it so have no comment on its effectiveness for me personally).
In Africa, we slept under netting when in mosquito territory. This works to some extent, except that the critters get inside while you are climbing in and out, and it is hard to be sure that you have the edges tucked in all night when you are tossing and turning.
As for diet, I have found that if I do not cut down on my diet which is high in fresh fruits, especially soft fruits like bananas, peaches, pears, plums, apricots, and dried fruits as well (we have lots of fruit trees at our house), the mosquitoes seem to be much attracted to me. Cutting out the soft fruits a week before going into mosquito country helps a bit, as does ramping up on garlic and onions - but only a little bit. In Africa, a large part of the diet includes bananas and other fruits.
Different people seem to attract more or less, even eating the same diet. Barb, for example, seems to be a major attractant (well, she is very sweet ;) ). Me not quite as much, and some friends seem to repel the beasts, sending them my way. 2 weeks on the trail with no change of clothes and lots of hot sweaty days doesn't seem to have any effect one way or the other, as far as the black flies, noseeums, and mosquitoes are concerned (hiking companions are a different matter, as are the tourists when we get back and head for a restaurant for a "real meal".