Miami Beach authorities started spraying for Zika-carrying mosquitoes Friday, and spraying’s expected to continue for weeks.
Authorities in other states are also cracking down on mosquitoes as the Zika threat worsens. It is the peak of mosquito season in the U.S., and the insects can be expected to continue biting until October in warmer states.
Aedes aegypti mosquitoes are the main carrier of Zika virus — as well as dengue, yellow fever and chikungunya — and they’re hard to fight because they bite during the day, live in or near houses and can breed in tiny amounts of water.
Here are some of the weapons available to fight disease-carrying mosquitoes:
Mosquito repellents let people move around with their own, personal mosquito protection. The most effective types interfere with a mosquito’s ability to sniff out a victim, usually by gumming up the receptors on their antennae.
Three top picks tested by the nonprofit group Consumer Reports this year use DEET, picaridan or a synthetic derivative of eucalyptus.
The Centers for Disease Control and Prevention says DEET is safe even for young children and pregnant women.
The CDC cautions that products with oil of lemon eucalyptus should not to be used on children under 3. They can cause a painful rash.
And while the chemical-sounding names may be off-putting, tests show they’re more effective than "natural" alternatives. "Five of the six plant-oil-based repellents we tested lasted an hour or less against Aedes mosquitoes, the kind than can spread Zika," Consumer Reports said.
They’re controversial and frighten many people, but the CDC says sometimes they’re the best solution for controlling large, disease-carrying populations of mosquitoes.
Widely used in the U.S. is a pesticide called naled, an organophosphate chemical that kills adult mosquitoes. Like most organophosphates, it's a nerve agent. It kills most flying insects so it should be used at night to spare bees and other beneficial insects.
The U.S. Environmental Protection Agency says when applied ultra-low volumes, naled doesn’t harm people — even toddlers playing in or eating grass in an area that’'s been sprayed.
Pyrethrins or pyrethroids are another widely used class of insecticides and are based on chemicals made by chrysanthemum flowers. They also are toxic to a wide range of flying insects and currently are not favored for fighting Aedes mosquitoes because the insects have developed resistance to them.
DDT works very well against mosquitoes but its use has been largely abandoned because it was so toxic to other insects and to birds. It's sometimes used to control malaria in Africa, Asia and South America and despite its bad reputation, studies have shown it is not very toxic to humans.
These are agents that kill the developing mosquito larva — those squiggly little creatures that spring up in rain barrels, ponds and other pools of water during mosquito season. Aedes mosquitoes are notoriously hard to fight because they lay their eggs in small containers and the larvae can grow in just a small amount of water.
Larvicides include natural agents such as Bacillus bacteria, whichinterfere with the ability of the larvae to digest food. That's often what's in mosquito "dunks" sold at hardware stores.
One larvicide called methoprene mimics developmental hormones found in insects but not in birds or mammals. It’s sometimes fed to cattle to stop flies from breeding in their dung.
These range from the sophisticated to the low-tech but the premise is the same in most: A scent is used to attract female mosquitoes, which are trapped when they enter to pay their eggs.
The CDC’s excited about one new trap that employs water and hay in a small barrel. It seems effective when a couple are set around a home in an Aedes-infested area.
Screens and air conditioning are very effective at protecting people from mosquitoes and the CDC says not to underestimate their benefits.
The best known is the Oxitec mosquito, genetically engineered to lay eggs that develop into faulty larvae.
The Food and Drug Administration says they’re safe to test but Oxitec has had trouble getting residents of Key West to buy into a plan to test them there. The company’s tested them in Brazil and other sites and say they can reduce local mosquito populations by as much as 90 percent.
The company says the GM mosquitoes would be safer for the environment and for people than the wide use of insecticides.
Another group has genetically modified mosquitoes so they only produce male offspring. Male mosquitoes don't bite. It's the females that need blood to produce healthy eggs.
A bacteria called Wolbachia can infect mosquitoes and for reasons that are not fully understood, it makes them sterile.
The University of Kentucky has licensed technology for breeding Wolbachia mosquitoes to MosquitoMate — a company founded by some of the university’s researchers. They’re working to test the mosquitoes to get EPA approval to use them. "We breed ZAP Males by infecting male mosquitoes with specific Wolbachia bacteria. When a female Tiger mosquito in your yard mates with a ZAP male, none of her eggs hatch," the company says.
Other groups are working on ways to make mosquitoes that carry destructive hormones or chemicals in or on their bodies.
The basic defense against mosquitoes is dumping the water they can breed in.