Now Dr. Vosshall, with her colleagues Mathias Ditzen and Maurizio Pellegrino, has uncovered DEET’s secret. It does indeed have something to do with smell: it jams odorant receptors in insect nervous systems, in effect masking odors that would ordinarily attract the bugs.
— Scientists have figured out how DEET, a commonly-used insect repellent, really works. Read more in The Secret of DEET? It Masks Odors That Usually Attract Bugs in the New York Times. Thanks to Sondra for the link!