Biology: June 2008 Archives


June 28, 2008

As I mentioned earlier, Netflix Instant Viewing (and hence the Roku) is pretty heavy on the cheezy 80s TV shows. Mrs. EG and I have been catching up on Forever Knight, the existential tale of a vampire living in Toronto, trying to become human, and making up for his sins by posing as a Canadian cop named Nick Knight (though not that polite, so you can tell he's not really Canadian). Anyway, in the Forever Knightiverse, it seems you can get along OK by drinking cow's blood, so we're back to the situation I alluded to in an earlier post, vampirism as an immortality treatment with some annoying side effects. Given that, it occurs that Mr. Knight would do a lot more good for people by starting a cow blood production operation and saving the lives of the terminally ill by turning them into vampires. Just saying.

June 15, 2008

Ditzen, Pellegrino, and Vauxhall had an interesting paper in science a few months ago about the insect repellent DEET and its mechanism of action. Their results seem to indicate that a significant fraction of the effect of DDT isn't so much insect repellence as blocking the attractant effect of 1-octen-3-ol, which is present in human breath. The figure below summarizes the observed behavioral results on drosophila:

At high concentrations of DEET and/or when flies can come in direct contact with the DEET, flies are repelled. I.e., they prefer an empty chamber without DEET to one with DEET. If you reduce the concentration of DEET to 10% and cover it with a perforated polypropylene barrier, the repellent effect is eliminated, and the flies end up equally in both vials. However, if you take the same pair of vials (one without DEET and one with DEET) and put food in both of them, then the flies far far prefer the one without DEET.

This is confirmed by direct studies of the fly (drosophila) and mosquito (anopholoes gambiae) sensory systems which show a significantly reduced response to 1-octen-3-ol in the presence of DEET (The other major attractant is CO2, but DEET doesn't seem to have much effect on that.) This kind of explains why DEET has a relatively short range of action: this NEJM article claims 4 cm, while Ditzen et al. claim 38 cm (I can't read either of the original sources) but in either case, it's pretty short. I wonder if part of the issue is that mosquitos are still attracted to other chemicals you're emitting (e.g., CO2) but they get confused when they can't smell the 1-octen-3-ol, so they get close but don't want to actually land on you. What you really want, though, is something that will convince mosquitos they want to be far away from you, not just that they don't want to be near you.