DAVIS — Identifying exactly how female mosquitoes detect their human prey is crucial to developing strategies for mosquito control and reducing mosquito bites, says chemical ecologist Walter Leal, professor of entomology at the University of California, Davis.

Leal, invited by editors of the international science journal Nature to write a "News and Views" piece, praised a scientific report by a Yale-Vanderbilt team as a "milestone discovery in our understanding of the malaria mosquito's sense of smell" and advocated more molecular studies in the war against malaria and other mosquito-borne diseases. 

Malaria, caused by a parasite transmitted by the Anopheles gambiae mosquito, threatens half of the world’s population and "is an accessory to the deaths of about 1 million humans every year," Leal wrote in the article, headlined “The Treacherous Scent of a Human.”

"Globally, the number of people who get malaria each year is greater than the population of the United States." 

Female mosquitoes "bite" because they require a blood meal to develop their eggs, he said. They detect their prey via olfactory receptor neurons found on their antennae, the equivalent to the human nose.  

Although it may be unclear exactly how malaria mosquitoes find their victims, human-derived odorants play a key role, said Leal, a noted authority on chemical ecology and a fellow of the Entomological Society of America. "For example, female mosquitoes find the odor of patients with malaria particularly attractive." 

The Yale-Vanderbilt team, headed by John Carlson of the Yale Department of Molecular, Cellular and Developmental Biology, examined 79 of the malaria mosquito’s odorant receptors, finding that some are well-tuned to detect specific human odors and others aren’t. Certain odorants activate some receptors but inhibit others, according to their comprehensive study published March 4 in Nature. 

"An exciting area for future research will be to see if any of the malaria mosquito’s odorant receptors are activated by DEET or mother mosquito repellents," Leal wrote in the accompanying "News and Views." 

Leal's lab discovered the secret mode of DEET, in groundbreaking research published Aug. 18, 2008 in the Proceedings of the National Academy of Sciences. The repellent does not jam the insect’s senses or mask the smell or the host, Leal said. Mosquitoes dislike the smell and avoid it.

An interesting aspect of the Yale-Vanderbilt work, the UC Davis chemical ecologist said, was comparing the sense of smell with the malaria mosquito with that of the fruit fly. Although the two share many receptions that detect aromatic compounds, fruit flies sense esters, the molecular signals associated with rotting fruit.

"These observations shed new light on how evolution has tuned olfaction in the two species according to their individual needs," Leal wrote.

Although Leal called for more molecular studies in the war against malaria, "the development of effective malaria control," he said, "will require a multidisciplinary approach that includes, but is not limited to, improvements to social infrastructure in countries affected by disease, vaccination programs and vector management." 

New mosquito attractants or repellents could be developed through reverse chemical ecology, determining which odorant attracts and which repels, Leal said. 

"This offers a fresh strategy for controlling the unwitting accessories to one of the world’s most prolific killers."