Professor discovers natural, non-toxic mosquito repellent


Molecular and Cellular Biology Professor Walter Leal published two papers in the Proceedings of the National Academy of Sciences in October, with far-reaching consequences for both mosquito and moth control. But perhaps the most exciting outcome of the works is his serendipitous discovery of a naturally occurring chemical that repels mosquitoes and could lead to effective, non-toxic protection from their disease-carrying bites.

The first paper, published October 28, focuses on the southern house mosquito's sense of smell. In it Leal's team identifies a large repertoire of olfactory genes through next-generation genetic sequencing.

About 10 years ago, Leal's lab at UC Davis found the first olfactory protein from all mosquito species by a labor-intensive process of isolating proteins, cloning and generating recombinant proteins for tests. Now, with the state-of-the-art technology available at the UC Davis Genome Center, Leal says they did almost the same amount of work to get the entire repertoire of olfactory proteins: hundreds of receptors and binding proteins.

A surprise amid all the data was that when Leal and his colleagues de-orphanized one of the newly discovered receptors, it responded very well to ethyl 2-phenylacetate.

"Initially we thought this is an attractant, because it is derived from plants, but when we tested it turned out that this is a repellent. This was great news because better repellents, particularly from natural sources, are needed to protect people from bites," Leal said.

Ethyl 2-phenylacetate has high potential as a repellant because it has low toxicity and is FDA-approved as a flavor.

Leal says that understanding the mosquito's sense of smell is scientifically important because the insects use their acute olfactory sense to locate hosts, egg-laying sites, and repellents. He hopes that this work will lead to opportunities to disrupt mosquitos' communication without harming the environment.

"When researchers understand how mosquitos perceive the environment through small chemical molecules like attractants from plants, humans, and places for them to lay eggs, we can mimic these signals and distract them without affecting other species, especially beneficial insects such as the honey bee," Leal said.

The southern house mosquito, a carrier of the West Nile Virus, lays about 200 eggs at a time in a single place.

"If we can lure them to the wrong place and trap them, we can in principle take out potentially 200 mosquitoes--about 100 females--from the environment," Leal said. "Also, we can use chemicals to minimize mosquito bites and, consequently, reduce transmission of diseases."

One of Leal's primary research goals is to find receptors that the southern house mosquito utilizes to find water pools for laying eggs and from there identify chemicals that may help researchers lure them. He says they have had some success, but still need better lures.

For the second paper, published by PNAS October 24 in collaboration with Nobel laureate Kurt Wuthrich, the researchers demonstrate evidence that pheromone-binding proteins in moths can be blocked, which may leave to the development of a new way to control their populations.

"Moth damage to U.S. agriculture alone exceeds $1 billion annually, thus the critical need for environmentally safe methods to control moth populations. This interruption of male-female communication could lead to reduced crop damage without toxic compound applications," Leal said.

But with all this, he also intends to launch new research into the repellent potential of ethyl 2-phenylacetate.

"Now that we serendipitously found receptors for an insect repellent and a novel repellent, we have to explore this path, too," Lead said. "The beauty of science is not to finding the answers to the questions we ask, but finding answers for question we did not have in mind."

Leal's mosquito research was funded by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health. Click here for the full paper.

His moth research work was funded by the U.S. Department of Agriculture-National Institute of Food and Agriculture. Click here for the full paper.