Mosquitoes ignore Deet after first exposure
Deet, the most popular insect repellent, was originally developed by the U.S. military to protect its soldiers during jungle warfare. For decades, it was effective, to the point that it became a common household item. Unfortunately, it appears that the chemical is losing its effectiveness as mosquitoes are becoming resistant to the spray. It appears that some mosquitoes are turned away only upon first exposure to Deet; after that, they appear to ignore it.
This is what researchers from the London School of Hygiene and Tropical Medicine found when they conducted a study in which a Deet-covered arm was exposed to mosquitoes. The first time the mosquitoes encountered the arm, they avoided it. Hours later, the test was repeated, and the same mosquitoes appeared to show little reason to avoid the human, despite the presence of Deet. When electrodes were attached to the mosquitoes' antennae, the results were confirmed: the mosquitoes were no longer sensitive to the chemical. The researchers concluded that this was a product of long-term genetic changes in mosquitoes, as well as temporary changes to the bugs' senses of smell.
Still, with many global diseases still transmitted by mosquitoes – including yellow fever, dengue fever and malaria – the researchers urged continued use of Deet until something new is developed.