Scientists explore mosquitoes’ radar that tells them who to bite

Anyone who has ever been bitten by a mosquito has wondered why are these insects attracted to me? Now, Johns Hopkins Medicine researchers may have an answer, according to a press release published last month.

They claim they have mapped specialized receptors on the insects’ nerve cells that are able to fine-tune their ability to detect particularly “welcoming” odors in human skin.

“Understanding the molecular biology of mosquito odor-sensing is key to developing new ways to avoid bites and the burdensome diseases they cause,” said Christopher Potter, Ph.D., associate professor of neuroscience at the Johns Hopkins University School of Medicine.

The new research is crucial as mosquito-borne diseases such as malaria, dengue fever, and West Nile virus afflict 700 million people and kill 750,000 each year. The hope of the research is to find better repellents that can interfere with odorant attraction.

Potter says the insects use multiple senses to find hosts (odorant, gustatory and ionotropic), but odorant receptors are thought to help mosquitoes distinguish between animals and humans while gustatory receptors detect carbon dioxide. 

For this work, Potter and postdoctoral researchers Joshua Raji and Joanna Konopka focused on ionotropic receptors because of their ability to guide a mosquito to prefer one type of human skin over another by responding to acids and amines. They looked for them in the insects' antennae.

Pinpointing genetic materials

They used a technique called fluorescent in situ hybridization, which pinpoints not the receptors themselves, but genetic material called RNA, a cousin of DNA. "Finding RNA linked to ionotropic receptors means that the neurons are highly likely to be producing such receptors," claimed the researchers.

The scientists noted that they found the majority of ionotropic receptors in the distal (farthest from the head) part of the antennae and that the antennae had more ionotropic receptors in the proximal (near the head) part of the mosquitoes. 

The results indicate that antennae are more complex than previously assumed.

Ionotropic receptors are known to work with “partner” receptors to respond to odors, “kind of like a dance partner,” added Potter. The research was also successful in pinpointing some pairings of receptors that predicted if an ionotropic receptor would respond to acids or amines, noted the statement. 

All this means that scientists are a few steps closer to finding possible mosquito repellents that actually work. This development, if successful, would allow humans to be better protected from the many diseases the insects bring. 

The study is published in Cell Reports.

Study abstract:

The mosquito’s antenna represents its main olfactory appendage for detecting volatile chemical cues from the environment. Whole-mount fluorescence in situ hybridization of ionotropic receptors (IRs) expressed in the antennae reveals that the antenna might be divisible into proximal and distal functional domains. The number of IR-positive cells appear stereotyped within each antennal segment (flagellomere). Highly expressed odor-tuning IRs exhibit distinct co-localization patterns with the IR coreceptors Ir8a, Ir25a, and Ir76b that might predict their functional properties. Genetic knockin and in vivo functional imaging of IR41c-expressing neurons indicate both odor-induced activation and inhibition in response to select amine compounds. Targeted mutagenesis of IR41c does not abolish behavioral responses to the amine compounds. Our study provides a comprehensive map of IR-expressing neurons in the main olfactory appendage of mosquitoes. These findings show organizing principles of Anopheles IR-expressing neurons, which might underlie their functional contribution to the detection of behaviorally relevant odors.