Hopkins scientists surprised at new finds on mosquitos’ reaction to repellants

March 17, 2022

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

In contrast, when odor sensors in fruit flies are forced to express odor receptors, it prompts flight from some smelly situations.

The findings, published March 8 in Cell Reports, reveal the variation in insect olfactory systems, say the researchers, and add to the growing body of research aimed at improving methods to repel mosquitoes from human skin.

Mosquito bites not only create irritating swelling and itching, but, worldwide, they play a role in spreading rampant and often lethal diseases such as malaria and dengue fever, as well as Zika virus infections.

“When experiments don’t go as predicted, there’s often something new to be discovered,” says Christopher Potter, Ph.D., associate professor of neuroscience at the Johns Hopkins University School of Medicine, describing the new study. It turns out, he says, that, “Mosquitoes are so much trickier than we thought.”

Potter and former postdoctoral fellow Sarah Maguire, Ph.D., designed their research project suspecting they’d find that mosquitoes have the same reaction as fruit flies when their new odor sensors are forced to be expressed.

Other research showed that when odor receptors in fly olfactory neurons are abnormally expressed, a new signal, based on the expressed odor receptor, is delivered to the brain, and the bugs move away from an offending odor.

The researchers then tested this same scenario on female Anopheles mosquitoes, whose bite transmits parasites that cause malaria in humans. The idea was that if researchers could push mosquito odor neurons into a similar expression state, triggered by odorants already on the skin, the mosquitoes would avoid the scent and fly off.

In the mosquito experiments, the researchers used mosquitoes genetically modified to overexpress an odor receptor called AgOR2, which responds to animal odorants found on humans.

By measuring the neuron activity generated by mosquitoes’ odor receptors, the scientists found that the mosquitoes with overexpressed AgOR2 receptors had very little response to common animal scents, benzaldehyde and indole, as well as chemical odorants in general.

Potter hopes that the current findings may advance the search for methods that can trick the mosquito olfactory system into no longer preferring the smell of humans.

Johns Hopkins Medicine News Release