It could be back to the drawing board for makers of insect repellants sooner than later, after European researchers discovered resistance to DEET, the active ingredient used in many products, can be passed on from some bugs to others rather quickly through the gene pool.

Experts were unsure why DEET (N,N-diethyl-meta-toluamide) repelled many bugs in the first place, and, for a long while, it was assumed that the chemical disrupted an insect's ability to smell. That is, until a 2008 study found mosquitoes avoided DEET's odor.

The "a ha!" moment came for scientists after they bred female yellow fever mosquitoes that were already equipped genetically to resist the smell of DEET with ordinary male mosquitoes. The number of mosquitoes that were born without DEET sensitivity more than quadrupled to more than 50 percent in a single generation. The difference-maker: Smell receptors on the antennae of some bugs doesn't work as well to detect DEET.

Nevertheless, some believe DEET's reign as the go-to insect repellant isn't over yet, considering it's taken a half-century for some bugs to begin to develop a resistance, and, among wild populations, the transition to resistance can be very slow.

Proceedings of the National Academy of Sciences May 3, 2010

healthfinder.gov May 3, 2010

Wired Science May 3, 2010