6 ways scientists are battling Zika-carrying mosquitoes

Mosquitoes are annoying as it is. But when they spread a virus that may cause birth defects, getting them under control becomes urgent.

The rise of the Zika virus is bringing greater attention to Aedes aegypti, the mosquito species that carries Zika, and to research into stopping the mosquitoes. Here are six approaches, from the established to the experimental, that scientists and officials are taking to control mosquitoes.

1. Take away their water

Removing pools of standing water, where mosquitoes congregate and breed, is the most recommended way to reduce their numbers. Some areas have gotten heavier rain in recent years, so pouring out and drying up potential breeding grounds is a little more challenging. And the Zika-bearing mosquito doesn’t need much water, laying eggs even in cups and small puddles, so vigilance is necessary.

2. Infect them first

Another possible preemptive strike against mosquitoes is germ warfare. Infecting mosquitoes with a bacterium called Wolbachia has been shown to prevent the dengue virus from replicating inside the insect, and resistance is passed down to offspring as well.

Researchers have released Wolbachia-infected mosquitoes in trials in Colombia, Australia, Vietnam, Indonesia, and Brazil, but analysis is still needed to determine if that lowered cases of dengue. And Australian scientists say preliminary evidence shows Wolbachia also battles Zika virus.

3. Ruin their reproduction

British company Oxitec is genetically modifying male mosquitoes to sabotage reproduction. When released into the wild, these GM mosquitoes compete with other males to mate with females, but their offspring die before adulthood. “So eventually the population will crash down,” said Hadyn Parry, CEO of Oxitec.

Oxitec has been testing these mosquitoes in the wild in Brazil for years, but in the wake of the Zika crisis the area covered by these trials has dramatically expanded.

4. Poison them

From household pest-control sprays to widespread crop dusting, insecticides are a longstanding and effective, if controversial, way to kill mosquitoes. The Zika crisis has led some public health experts to call for the banned insecticide DDT to be brought out of retirement. Experts on mosquito control, however, say it likely wouldn’t work, since mosquitoes evolve resistance to insecticides over time. Other insecticides are being used to fumigate homes across the Americas.

5. Make them fish food

An initiative that started in 2012 in El Salvador showed that simple fish ponds could be effective at fighting mosquitoes. Volunteers gave tilapia and sambo fish, which feed on mosquito larvae, to households to keep in open barrels and other water catchments. The program successfully reduced mosquito-borne illness rates in that town, and has since expanded to six other coastal towns. However whether it would be effective against Zika is an open question, given that the bugs breed in such tiny pools of water.

6. Add a kill switch

The still-experimental “gene drive” technique could allow scientists to genetically modify a whole population of mosquitoes to be resistant to Zika — or it could kill them entirely. Gene drive essentially “hijacks” evolution by forcing added DNA to rapidly propagate throughout a population.

Scientists have used gene drive to create mosquitoes unable to transmit malaria as well as sterile mosquitoes. The latter approach would be promising for Zika, but scientists say so far no funding exists for that research.