In a move that could have far-reaching implications for equatorial countries, Canadian researchers have developed a cheap, effective and non-toxic way to dramatically reduce disease-carrying mosquito populations by using a ubiquitous item that, ironically enough, the pests love to breed in: old tyres.
“We are turning a weapon that mosquitoes use against us – old tyres – against them,” says Dr. Gerardo Ulibarri, PhD, an associate professor of medicinal chemistry and eco-health at Laurentian University in Sudbury, Ontario. He developed the device, known as an ovillanta (loosely translated, it’s Spanish for “tyre for laying eggs”), to destroy the larvae of the Aedes, a genus of mosquito that carries the now-notorious Zika virus as well as the dengue, chikungunya and yellow fever viruses.
The ovillanta offers a win-win-win situation in the war against these diseases, which together afflict millions of people annually – primarily in tropical countries – and result in tens of thousands of fatalities, according to data from the World Health Organization.
For starters, the devices eliminate the need to use pesticides that can damage the environment and carry the risk of collateral damage to other insects – including those that eat mosquitoes. Furthermore, subsequent generations of mosquitoes can build up resistance to pesticides, making them less and less effective, Ulibarri notes.
The devices also provide an answer – albeit a small one – for one of the world’s most intractable waste-disposal problems: What to do with old tyres. Moreover, the traps are inexpensive and relatively easy to make, and the there’s an almost inexhaustible supply of materials available (an estimated 1.5b tyres get discarded annually worldwide).
Ulibarri had developed another type of trap to help stem a 2012 outbreak of the West Nile virus in Ontario, but it proved too costly and complicated to transport to developing countries. “So I started to look at local materials and came up with tyres because almost 30 percent of Aedes mosquitoes breed in car tyres filled with water,” he explains. “We didn’t plan it that way – it was total serendipity.”
Researchers found that 84 ovillantas placed in seven neighborhoods in the town of Sayaxche destroyed more than 18,000 Aedes larvae per month. That’s nearly seven times better than standard traps.
Initial tests show the ovillanta is very effective. During a 10-month study in Guatemala, researchers found that 84 ovillantas placed in seven neighborhoods in the town of Sayaxche destroyed more than 18,000 Aedes larvae per month. That’s nearly seven times better than standard traps. And equally as noteworthy, no new cases of dengue were reported in the area during that period; typically, about two to three dozen cases would occur during that time, Ulibarri says.
The ovillanta, which consists of two roughly 20-inch-long pieces of tyre and a tube drain valve, mimics an Aedes breeding site; three devices can be made from one tyre. Here’s how it works: The bottom half of the device gets filled with about 2 litres of water, topped with so-called “landing strips” – pieces of Pellon or germinating paper, for example – on which the female mosquitoes lay eggs.
Vehicle of Destruction
“Mosquitoes will not lay eggs on a dry surface – they need moisture to hatch,” Ulibarri says. “In a hot climate, you have to add water from time to time because it evaporates very quickly.” The water in the device must be drained about twice a week into a receptacle covered with a filter; something as simple as a piece of white cloth works well because the color makes the larvae clearly visible, he notes.
After that, users destroy the eggs, pour the water back into the ovillanta (topping it off with fresh water) and install two new landing strips. “It’s important to recycle the water because after the eggs hatch, they release a pheromone into the water that tells other mosquitoes it’s a good, safe place to lay eggs,” says Ulibarri, who’s work is funded by Grand Challenges Canada. “Understanding the enemy is the best way to fight it.”
It usually takes about one month – the average life cycle of a female Aedes in hot weather – before the traps start making a dent in local mosquito populations. As few as two ovillantas per acre can significantly decrease mosquito populations, but the more there are, the better the results, Ulibarri says.
So far, the devices have been tested in Guatemala and Mexico, and Ulibarri says his team has been invited to do more testing in Brazil and Paraguay. What kind of potential does the ovillanta possess?
“I think that if properly used, it can have a very strong impact on different diseases such as Zika, dengue, chikungunya and yellow fever. And with a different attractant, we also might be able to fight the Culex and Anopheles mosquitoes (which carry the West Nile and malaria viruses, respectively),” Ulibarri says. “If we all work together, maybe we can make a difference after all.”[기사/사진: BBC]