Mosquitoes can develop a resistance to substances used to repel them. This has been shown for the first time in laboratory tests at the Swedish University of Agricultural Sciences (SLU) and associates in the UK.

It is the yellow fever mosquito that has developed a resistance to the mosquito repellent DEET, a substance used in mosquito repellents all over the world. In Sweden it is found in the products MyggA and Djungelolja (Jungle Oil). The capacity of mosquitoes to develop resistance has been shown to be hereditary.

"Through testing, we have found that yellow fever mosquitoes no long sense the smell of DEET and are thereby not repelled by it. This is because a certain type of sensory cell on the mosquito's antenna is no longer active" says Rickard Ignell, a researcher at the Division for Chemical Ecology at SLU in Alnarp.

Rickard Ignell performed the research in collaboration with Rothamstead Research in the UK. The findings were recently published in the scientific journal Proceedings of National Academy of Sciences (PNAS).

The scientists have thus seen that the sensory cell on the mosquito's antenna has stopped reacting to DEET. This have many explanations, such as the protein that binds in to DEET having mutated.

"More research is needed to find out what the mechanism is," says Rickard Ignell.

The researchers are now urging restrictiveness in the use of DEET and other mosquito repellents on a large scale in a limited area, in order not to make other mosquito species resistant.