DEET is the mother of all mosquito repellants. Its strong stench keeps bugs at bay by affronting their olfactory systems with an intensely offensive odor. But scientists are now running into a problem with DEET’s effectiveness: after three hours the stuff no longer deters buzzing biters.
N,N-Diethyl-3-methylbenzamide, a.k.a. DEET, first emerged as a pesticide for crops, but the U.S. military then developed the chemical for use against biting insects in jungle environments during World War II. Available as a spray or a lotion, DEET is still used today to repel flies, ticks and mosquitoes, and to protect against the diseases these bugs can transmit.
But now, researchers in London have shown that three hours after Aedes aegypti mosquitoes were exposed to DEET, they seemed to become immune to the smell and were no longer repulsed by it. This species, also known as the yellow fever mosquito, is notorious for spreading tropical diseases.
Every summer since West Nile virus’s first U.S. appearance in 1999, Americans have listened to warnings about the mosquito-borne disease and its potentially deadly effects, a severe flu-like fever sometimes accompanied by an even more dangerous brain inflammation. Because the disease—and its attendant worries—recur every year, it’s easy to tune out West Nile coverage. But the Center for Disease Control has announced that this year’s outbreak is shaping up to be one of America’s worst, with the current count at 1,118 cases and 41 deaths. About half the reports come from a single state: Texas.