How do mosquitoes detect DEET? Research from the US indicates it’s not only by smell, but through contact as well.
DEET is generally considered the gold standard in terms of personal insect repellent. Previous research and hypothesis has suggested that the ‘bitter’ taste of DEET repels mosquitoes and stops them biting. However, new research from Rockefeller University in the US suggests that this may not be the whole story.
Researchers carried out a series of experiments which demonstrated that DEET acts through three distinct mechanisms: smell, ingestion and contact.
It’s well established that mosquitoes will not approach DEET-treated skin, demonstrating the strong olfactory element in DEET repellency. In order to evaluate the potential impact of other senses in DEET repellency, the researchers used orco mosquito mutants, which had lost their olfactory sense and therefore were not repelled by the smell of DEET.
To evaluate taste and ingestion, researchers added DEET and other ‘bitter’ chemicals to sugar water. The mosquitoes had a clear preference for sugar water without DEET or other bitter compounds.
By providing mosquitoes with a blood source underneath an artificial membrane, the role of contact could be evaluated. Blood containing DEET or bittering agents was not ingested by female mosquitoes. However, when the bittering agents were rubbed on the surface of the artificial membrane with normal blood on offer underneath, the mosquitoes landed and fed quite happily. However, when the membrane was treated with DEET, the mosquitoes would move away rapidly after landing or touching the treated skin. When the experiment was rigged to prevent the mosquitoes landing, they were able to feed.
Mosquito legs, like their mouthparts, are covered in tiny hairs that can sense molecules. These experiments demonstrated that mosquitoes can detect DEET through their legs, illustrating the importance of achieving complete coverage of exposed skin to provide protection from biting mosquitoes.
More information on mosquitoes.
Further reading: Dennis, E.J et al (2019). Aedes aegypti Mosquitoes Use Their Legs to Sense DEET on Contact. Current Biology. 29: 9, P 1551-1556