How are mosquitoes able to avoid insect repellents?

In what they call surprise findings, Johns Hopkins Medicine scientists report that unlike fruit flies, mosquitoes' odour sensing nerve cells shut down when those cells are forced to produce odour-related proteins, or receptors, on the surface of the cell. This "expression" process apparently makes the bugs able to ignore common insect repellents.

In contrast, when odour sensors in fruit flies are forced to express odour receptors, it prompts flight from some smelly situations. So the researchers designed their research project suspecting they'd find that mosquitoes have the same reaction as fruit flies when their new odour sensors are forced to be expressed.

The researchers then tested this on female Anopheles mosquitoes. The idea was that if researchers could push mosquito odour neurons into a similar expression state, triggered by odorants already on the skin, the mosquitoes would avoid the scent and fly off. But they found that the mosquitoes had very little response to common animal scents, benzaldehyde and indole, as well as chemical odorants in general, says a press release.

The researchers tested how mosquitoes modified to overexpress an odour receptor that responded to odorants in common insect repellents, such as lemongrass. They found that the genetically modified mosquitoes were able to ignore insect repellents.

The researchers suspect that the odour receptor shutdown may be a kind of failsafe in mosquitoes, ensuring that only one type of odorant receptor is expressed at a single time. Mosquitoes have been found to be trickier than initially thought.