This one started out, for me, as a personal observation. Our family's currently camping (I'm sitting at a picnic table right now), and something curious happened last night. My wife, who had thoroughly doused herself with highly concentrated (25% DEET) OFF!®, was feasted upon just a foot or two from me, while I enjoyed a total but unexplained protection. This is our first major exposure to mosquitoes since starting the diet, now that I think of it, and this was not the normal state of affairs pre-diet. Mosquitoes positively loved me.
My wife, as it happens, is trying to get back on the proverbial wagon, but she is currently not in ketosis. Naturally, I thought of this as a possible factor, even if I couldn't explain how it would work. So I did some research.
It turns out that ketones (some of them more than others) are natural and effective mosquito repellents. According to some research, some of these compounds are considerably more effective (and less harmful) than DEET. Now they're trying to productize ketones as spray-on repellents.
As an experiment, I'm planning to go the rest of the camping trip without using any artificial repellents, and see how I fare. That's not exactly a rigorous double-blind, placebo-controlled trial, but it'll help me personally evaluate the voracity of this possibility.
As planned, I went the rest of the camping trip without the aid of artificial mosquito repellents, and I'm thrilled to report that I got not a single bite. This has led me to consider how primitive sub-Saharan tribes have managed to survive the scourge of Malaria that has plagued the rest of the African continent. I plan to keep looking into this.