New Repellent Coming Soon? Scientists Discover How to Gross Out Mosquitoes

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A man walking his dog, stops to examine an Aedes aegypti mosquito sculpture created by street artist Andre Farkas, on a Paulista Ave. sidewalk, in Sao Paulo, Brazil, Friday, May 27, 2016.
A man walking his dog, stops to examine an Aedes aegypti mosquito sculpture created by street artist Andre Farkas, on a Paulista Ave. sidewalk, in Sao Paulo, Brazil, Friday, May 27, 2016. Credit: Andre Penner/AP

A discovery made in Texas could lead to a whole new generation of mosquito repellents, say scientists who accidentally found a way to make the insects reject food.

The receptor is related to sugar consumption, but if the same aversion could be associated with blood feeding, a totally new and effective mosquito deterrent could be developed, say the scientists.

The relevant mosquito is the female. Males are fructivores – they only eat sugar syrup anyway. It is the ladies that feed on blood, which they need in order to lay eggs. No blood, no protein, no procreation.

After mating, the female mosquitoes immediately seek out a blood meal, preferably from their favorite – a human host. If we aren't available, the female will eat sugar syrup, which in nature means nectar from flowers, usually.

What the team discovered is that adding a certain synthetic protein to the sugar syrup repels the little beasts, caused them to scuttle away from the meal, says Dr. Patricia Pietrantonio of the Texas A&M University, College Station's Entomology Department, who made the discovery with her students and colleagues from elsewhere.

Their findings are published in the paper "Leucokinin mimetic elicits aversive behavior in mosquito Aedes aegypti (L.) and inhibits the sugar taste neuron." 

"This finding could lead to novel mosquito repellents," stated chief entomologist Dr David Ragsdale. "This is really a big deal, a major achievement," and added: "With Zika a looming threat, this is a timely discovery."

Fooling the Zika mosquito

The tests were done on Aedes aegypti, which is the mosquito species most associated with the spread of Zika, though other species can spread the virus too. Aedes aegypti mosquitoes exist almost worldwide (see map, of the mosquito's range, and known incidences of Zika).

Map shows distribution of mosquitoes that spread Zika, and Zika itself.Credit: Ruth Schuster

Zika had been thought to be a rather benign disease, but recent evidence has linked it with extremely grave birth defects, including microcephaly, as well as disease in adults. Aedes aegypti also spreads dengue, yellow fever and Chikungunya viruses, by the way.

As for the discovery, it is, specifically, that the females rejected a solution with sucrose that included a synthetic peptide. We know whether or not the mosquitoes ate the sugar syrup because the scientists dyed it blue, so they could trace the meal through their little guts.

For unrelated reasons that we won't get into, one of the team members had designed an artificial protein that mimics kinins, which are protein-based diuretic hormones in mosquitoes.

Yes, those are hormones that make mosquitoes pee, or as Pietrantonio puts it, "These diuretic hormones make mosquitoes lose water after a blood meal."

To their surprise, the scientists discovered that their fake protein (a "peptidomimetic") blocked the mosquitoes' sugar perception. They couldn't find it. "This is a completely new and unexpected discovery," Pietrantonio says.

The sucrose in the sugar solution activates receptors located on the little legs and mouths of the mosquitoes – but when the ersatz kinin was in the juice, the mosquitoes didn't feed, they flew off.

Now, if that aversion could be tied to blood meals, Pietrantonio says, a totally new and effective mosquito feeding deterrent could be developed. If the mosquito doesn't eat blood she can't lay eggs. QED. However, this is far from being accomplished, Pietrantonio qualified – and vowed that the team will continue to study the system, hoping to develop an effective mosquito feeding deterrent.

And not a moment too soon. While several cases of Zika have been detected in Israel (nine so far), none were contracted locally. All the cases were infected abroad. But not only is Aedes aegypti, its host, endemic to Israel: the tiger mosquito which also carries the disease has arrived.  The World Health Organization even warned that Israel's risk of Zika becoming endemic isn't low, it's moderate.

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