DEET, a substance known for its insect repellent, seems to deter mosquitoes in three different ways. Mosquitoes have long been known to avoid the smell and taste of DEET, but now American researchers have shown that the mosquito's own legs are also sensitive to the substance. Yellow fever mosquitoes (Aedes aegypti) would therefore prefer not to land on the skin wiped with DEET. Researchers write this week in the journal under the direction of Leslie Vosshall of Rockefeller University in New York Current biology.
DEET is a yellowish oily substance that does not evaporate very quickly. On the one hand, this is beneficial because the applied layer remains effective for longer, but, on the other hand, the effect of repelling mosquito from the odor is limited as a result. This means that it only repels insects when they approach, and that, for example, bracelets impregnated with DEET do not work. But whoever covers all the exposed parts of the skin with the material is protected from mosquito bites for hours.
"This research explains why mosquitoes fly irritated skin treated with DEET," says mosquito specialist Willem Takken of Wageningen University in an answer. "The fact that rejection also occurs in contact corresponds to the observations we have made in our own research. Researchers are showing for the first time that the legs of mosquitoes also contain receptors for volatile compounds. "
The Vosshall group has already discovered that mosquitoes that lost their sense of smell due to a mutation in DNA were no longer deterred by the smell of DEET (Nature, 2013). However, it was noticeable that these mosquitoes were delayed by direct contact with the DEET.
They may have tasted the substance that people describe as bitter. People who use DEET also get some of this substance in their blood. But it is not clear whether the bitter taste it causes helps prevent mosquito bites.
In the new study, Vosshall and his colleagues demonstrate, with a series of tests, that the legs of the mosquito are sensitive to DEET. A volunteer applied DEET and put a long glove with a millimeter and a half hole where the mosquito could put the muzzle exactly. In this way, only the parts of the mosquito's mouth came in contact with the DEET, but their feet remained in the latex of the glove. Mosquitoes were not left by DEET and bite with the same frequency as control mosquitoes on untreated skin.
With larger holes in the glove where the mosquito's paws were on the treated skin, DEET proved to be repellent. Then there had to be something in the mosquito's legs, the researchers reasoned. They first tried the mosquitoes where they cut the ends of the legs, but this gave unreliable results because the mosquitoes need their legs to be able to put enough force to pierce the skin.
The researchers therefore isolated the legs in a subsequent test with a layer of quick-drying glue. This is a method that has been previously tested with fruit flies, which they can observe with their feet if they are walking on something edible. Mosquitoes in which the extremities of the legs (tarsi) were all isolated were no longer sensitive to DEET on the skin. In other tests, the researchers showed that sensitivity to DEET is found in all pairs of yellow fever mosquito legs.
"This study does not make much difference in practice," Takken responds soberly. DEET effectively repels mosquitoes in any way. But Vosshall hopes that this insight can lead to the development of new insect repellent products that use sensitive mosquito legs.
In addition to protecting against mosquitoes, DEET also protects against stabbing, ticks and leeches. If they also avoid direct contact with the substance is unknown.