Could this be the end of the mosquito?

By Tori Marlan  

Molecular biologist Steve Whyard is trying to spare himself and others from itchy bites—and, more importantly, mosquito-borne diseases. 

A professor in UM’s Department of Biological Sciences, Whyard keeps the mosquitoes in a campus insectary, a room controlled by light and temperature. He tends to the colony with the help of his students. 

Every few days, the researchers sprinkle pellets of crushed-up rabbit food into covered tubs of water. The larvae inside feast on bacteria that forms on the pellets, enabling them to grow, develop and eventually undergo metamorphosis. In a week or two, they become adults buzzing around in a screened cage. 

On occasion Whyard and his students get surprised by escapees.

“I’m always disappointed when we have to use a fly swatter to kill a mosquito,” he says, “because I want my biotech to kill a mosquito.”   

Whyard considers mosquitoes a “marvel of engineering” and has devoted his career to understanding them and developing techniques to control their numbers. He finds these tiny creatures “fascinating.”

“In an evil kind of way,” he adds.  

His work involves targeting the mosquito’s genes with special RNA [ribonucleic acid] molecules he makes synthetically, in order to kill the insect outright or modify it.

Whyard applies what he’s learned from his research on the genes involved in sex differentiation. Along with crushed-up rabbit pellets, he feeds RNA molecules to the larvae to sterilize male mosquitoes and to try to knock out genes involved in female-specific development. 

He’s trying to delay female development and create an entire population of males that can’t reproduce. “We’re not quite there yet, but we’re really close,” he says. “We’ve got almost 99 per cent sterility.” 

Whyard says the RNA molecules get into mosquitoes’ guts and tissues but don’t alter their DNA. The sterilization isn’t heritable, but it could cause a population crash.  

Mosquitoes are a resilient, ancient group of insects—contemporaries of the dinosaurs that date back 100 million years. Most of the species that exist today—there are about 3,000—have been around for a few million years. Canada is home to roughly 80 of those species. 

The tropical mosquitoes in Whyard’s insectary belong to the species Aedes aegypti, a vector for yellow fever, dengue and the Zika virus. They’re closely related to Aedes vexans, the most common mosquito species in Manitoba and one that’s so prevalent, Whyard says it’s jokingly referred to as “the provincial bird.”   

Most species feed only at dusk, but Aedes vexans is more of an opportunist and during cloudy or cooler days it “will get you day and evening,” he says.  

While the population-control techniques Whyard has developed are species specific, he says they’re translatable to other mosquito species as well as other types of insects, including crop pests. 

With his sterilization method basically “nailed down,” Whyard says he’s ready to move from the laboratory to field testing—“but I’m going to probably need some extra funding for that.”  

In the meantime, he’s trying to figure out other ways to stop the bites.  

Since female mosquitoes find their victims with the olfactory receptors on their antennae, Whyard is focusing on understanding their sense of smell so he can control their behaviour. (Only female mosquitoes dine on blood, which they need to produce eggs. Males survive on flower nectar.) 

The species in Whyard’s insectary can detect the scent of carbon dioxide plumes coming from people’s breath from about 50 metres away. In the wild, they follow that scent, and then, when they get within 10 metres of a person, they start to discriminate, deciding whom to zero in on based on the “cocktails of odours” that the potential hosts are emitting. 

“Some people are tastier than others,” explains Whyard, who is also UM’s Associate Dean of Research for the Faculty of Science.

Human sweat contains various compounds, including lactic acid, ammonia, and uric acid, all in combinations that vary from person to person. Diet also plays a role in the scents emanating from skin.  

Mosquitoes don’t like sulfur-containing compounds, so if you’ve been eating onions or garlic, or cruciferous vegetables such as broccoli or cabbage, you’re a little less likely to smell good to mosquitoes than people who avoid those foods. 

But it’s not just your own odours that attract mosquitoes. The skin’s microbiome factors into the mix, metabolizing the components of sweat and producing other volatiles. The mosquitoes are drawn to those odours as well.   

By decoding the odours that mosquitoes find attractive and understanding the receptors that bind them, Whyard aims to, literally, throw mosquitoes off the scent. 

“I’m talking with my chemist friends, asking them to design me a new molecule that looks like the odorant, but just slightly different, that’s going to mess with that receptor’s function. Basically, what I’m looking for is a new repellent.”