What makes mosquitoes avoid DEET? An answer in their legs

Many of us are crouching in the DEET every summer in the hope of avoiding mosquito bites, and it usually works pretty well. Now the researchers reporting in the newspaper Current biology On April 25, we made the surprising discovery that the success of DEET lies partly in the legs of the mosquito, not in biting bites.

"We show that while mosquitoes find DEET and bitters equally unpleasant to ingest, only DEET repels mosquitoes by contact," said Emily Dennis of Rockefeller University and Howard Hughes Medical Institute. .

The researchers explained that the results could help in the search for even better and more durable insect repellent products.

Dennis and Leslie Vosshall and their colleagues had already developed mutant mosquitoes that lose some of their sense of smell, including the part needed to avoid DEET-treated arms. While normal mosquitoes avoid DEET, these mutants remained attracted to people even when they were covered with repellent. But despite this attraction, they did not really bite. This is because they have been pushed back into contact by a DEET-laden skin.

The question was: why? Other researchers have shown years ago that DEET may have a bitter taste and hypothesized that bitter taste could explain its ability to repel mosquitoes on contact.

To test this idea, the researchers first made sure that the mosquitoes do not appreciate the bitter flavors or taste of DEET by offering them sweetened water with or without DEET or another bitter compound. As might be expected, the insects had a clear preference for sugar water without biting or DEET.

Then they coated their arms with bitter compounds, and they were surprised to see that the mosquitoes continued to feed on blood. In fact, they would continue to bite even when these bitter compounds were present at a concentration ten times greater than that used in sugar-drinking experiments.

This suggested that insects avoided the DEET even though they could not smell, this was not due to a bad taste in the mouth. To further explore, they offered mosquitoes warm blood under a membrane that they had to puncture for drinking. When DEET or bitters were mixed in the blood, the insects were not interested in drinking. When the bitters were spread on the membrane, the mozzies continued to land and drink blood. But they discovered that a layer of DEET on the surface of the membrane was incredibly effective in preventing buzzing insects from coming into contact.

"We were then convinced that DEET was doing something interesting and quite unique on the surface of the skin," Dennis said.

Mosquitoes and other insects have tiny hairs on their mouthparts and paws that can detect molecules. This means that, just like our languages, their legs have the ability to taste. Additional experiments showed that mosquitoes continued to feed on DEET-treated arms only when researchers had adjusted them so that their legs did not touch the skin. He told them that the legs of a mosquito are important for detecting DEET.

This study is the first to experimentally separate the various effects of DEET and identify the parts of the body that mosquitoes need to detect the repellent. The researchers say the results will allow them and others to identify the neurons and essential proteins involved, with important implications for the development of new repellents.

"DEET is the most effective repellent available on the market, and it's possible that other repellents will fail because they can only mimic one or two aspects of its operation," Dennis said. "If the key to DEET's effectiveness lies in its ability to act in different ways on all sensory systems, knowing what it is can help us detect potentially new, more durable repellents."