Why it’s so hard to zap the Zika mosquito, and what we can do

The little black Aedes aegypti mosquito with its white-striped legs and body seems harmless enough. But it can spread the Zika virus, which is tentatively linked to birth defects in babies.

Aedes aegypti mosquitoes are thought to have originated in Africa and migrated to other tropical and subtropical parts of the world through travel and trade.

They are tough bugs to control, and the World Health Organization has called them “opportunistic” for their ability to adapt to environmental changes.

“Most ominously, Aedes aegypti mosquitoes, which long bred in water collected in tree holes and the axils of plant leaves in forests, have adapted to breed in urban areas, flourishing in impoverished crowded areas with no piped water and poorly collected garbage and trash,” WHO wrote in its latest assessment.

Here’s what makes the bug so hard to control:

Quick life cycles

Mosquitoes lay about 100 eggs at a time. From the moment the egg is laid, it can take as little as 10 days for adult mosquitoes to take flight.

Hardy eggs

Female mosquitoes lay their eggs on the rims of water containers. The eggs stick to a container’s walls and can survive, even in a dried-out state, for up to eight months.

Small water sources

Only a small amount of water is necessary to cover the eggs — a rain shower can provide enough standing water for larvae to develop. The larvae can grow in wet places as tiny as a bottle cap, the NewsHour’s science correspondent Miles O’Brien reported.

Sneak attacks

Only the female mosquitoes bite, and they feed mostly around dusk and dawn. But they also bite at night in well-lit homes, hiding in closets and under beds, according to WHO’s report.

Human blood

The mosquitoes prefer to bite humans over other mammals and take small sips from multiple bites, which increases the likelihood that they will infect multiple people.

A map from the Centers for Disease Control and Prevention shows the countries where Zika virus is actively transmitted as of Feb. 3, 2016. Brazil has been particularly hard hit.

A map from the Centers for Disease Control and Prevention shows the countries where Zika virus is actively transmitted as of Feb. 3, 2016. Brazil has been particularly hard hit.

Past tactics

The use of insecticides after the mosquito was first discovered in the 1940s helped to nearly eradicate Aedes aegypti in the Americas. But as the health threat waned, so did efforts to control the mosquito, and the insect thrived, according to WHO.

Over time, the mosquitoes developed a resistance to insecticides. And at the same time, human populations grew, creating environments that were conducive to mosquito breeding.

What can we do now?

The World Health Organization encourages countries to use “old and new approaches” to mosquito control, including:

  • Fumigating adult mosquitoes during the dusk and dawn feeding times for greatest effectiveness
  • Evaluating the use of genetically modified mosquitoes to reduce the Aedes aegypti populations
  • Developing the technique of sterilizing male insects with low doses of radiation, which makes the females’ eggs non-viable
  • Introducing male mosquitoes carrying the naturally occurring Wolbachia bacteria, which doesn’t infect humans but prevents female mosquitoes from producing viable eggs
  • Using other biological methods, such as putting larvae-eating fish in water storage containers, like El Salvador has begun to do
  • And until a Zika vaccine is developed, using personal protections where Zika outbreaks have occurred such as applying bug spray with DEET, wearing long sleeves and pants, and sleeping under mosquito nets.