Yesterday the BBC reported findings from the London School of Hygiene and Tropical Medicine which indicates that mosquitoes are becoming increasingly resistant to DEET (N,N-Diethyl-m-toluamide).
DEET, developed by the US military in 1946 for use in jungle warfare, remains one of the most prevalent insect repellent ingredients.
While DEET still deters mosquitoes upon their first exposure, the insects subsequently show little to no aversion to the chemical afterwards.
In tests, researchers offered an exposed volunteer's arm covered in DEET to mosquitoes as bait. Hours later, they offered another arm covered in Deet to the same group of mosquitoes. What they observed was a marked decrease in DEET's effectiveness.
Investigating further, researchers attached electrodes to the mosquitoes' antennae. Data gained concerning the receptors' responses to DEET indicated the mosquitoes experienced a reduced sensitivity to the chemical.
Dr. Logan of the institute speculates that "there is something about being exposed to the chemical that first time that changes their olfactory system - changes their sense of smell and their ability to smell DEET, which makes it less effective."
The London School of Hygiene and Tropical Medicine's report, "Aedes aegypti Mosquitoes Exhibit Decreased Repellency by DEET following Previous Exposure," is published and can be accessed in the journal Plos One.