Citronella candles are great for setting a mood, but they’re not so great for the very thing they’re advertised to do: repel mosquitoes. That’s one conclusion from a new study that tested 11 types of repellents on Aedes aegypti mosquitoes—the vectors of Zika, yellow fever, dengue, and other diseases. To find out which ones worked best, scientists developed a lab test designed to mimic the conditions on someone’s backyard patio. A human sat at one end of a wind tunnel as “bait,” while scientists measured how many mosquitoes moved toward their target, depending on which repellent was used: one of five sprays, five wearable devices, or a citronella candle.
Most did not live up to the promises on their labels. At a distance of 1 meter, DEET and oil of lemon eucalyptus sprays reduced mosquito attraction by 60%. The only wearable device that worked was an OFF! clip-on fan containing the insecticide metofluthrin. The rest of the products had a weak repellent effect or were no better than no protection at all, the researchers report today in the Journal of Insect Science. Two devices in particular came under harsh criticism from the scientists: bracelets containing herbal extracts and sonic mosquito repellers, which claim to use high-frequency sound to drive away mosquitoes.