The annual mosquito massacre...in your hometown
The next time you go outside to fight mosquitoes, know this: You aren't alone. No matter where you live, chances are there's a local mosquito control program trying to reduce the spread of disease and improve quality of life by targeting the insects.
You've probably seen them rolling through the neighborhood in the mosquito control truck, or maybe flying overheard a few hundred feet off the ground, trailing a foul-smelling fog that kills mosquitoes and gives everyone a few hours' peace.
But mosquito spray is a last resort, and what most people see is only a small part of a community's overall mosquito control plan.
They're usually county-wide operations that run from late spring to early fall – year-round if you live somewhere warm – testing for infected mosquitoes, cleaning up their breeding grounds, and pinpointing their habitats so that crews can methodically eliminate them by the thousands.
Most local programs will even come out to your house and give you a hand if you're having a particular mosquito problem.
Trouble is, these programs, which you help fund, by the way, can't get rid of every mosquito in every neighborhood. They can only help cut down on the population. And they can't do it without plenty of cooperation from the public.
So, you still have to practice some DIY mosquito control of your own, especially if you don't want bugs fleeing the official exterminators only to settle in your yard.
Where does mosquito control start?
Professional mosquito hunters have taken to calling their programs IMM, for integrated mosquito management. That means they no longer just go out once a week, spray a few areas with insecticide, and call it a job well done. These days, effective mosquito control programs target four key areas:
- Surveillance – The regular trapping and testing of mosquitoes to find out what species are causing problems, how many there are, and whether any of the mosquitoes are carrying West Nile virus, malaria, or some other disease they can transmit to people.
- Source reduction – Cleaning up stagnant ponds, managing stormwater drainage systems, and digging ditches around marshy areas to help cut down on the number of places where mosquitoes can actually lay and hatch eggs. This includes getting people to dump the myriad containers around their yards that can serve as mosquito breeding grounds.
- Larvacide – Finding ways, both biological and chemical, to kill mosquitoes while they are still in the larval stage living in water. This could mean putting bacteria or oil in the water to poison the larvae, or introducing natural predators to feed on them.
- Adulticide – The method of last resort, using mosquito spray to kill large numbers of adults as they fly and feed. Crews release insecticides from planes and trucks over targeted areas at specific times so they can get as many as possible in one shot. Helps to eliminate females before they have a chance to lay eggs. Also a necessity after storms cause heavy flooding because huge swarms will soon follow.
None of the methods are effective by themselves, but have to be combined to attack every stage of the mosquito life cycle. Otherwise, no matter how many bugs the crews killed, there would be millions more waiting to take their place.
The mosquito stakeout
The first step in fixing a problem is figuring out what it is. Obviously mosquitoes are the problem, but mosquito control crews need to know more than that. They also have to identify specifically which ones are causing the trouble and where.
There are more than 150 species of mosquitoes in the United States, and while some are known to be potential health hazards – like the Anopheles mosquito, a malaria, carrier – a species that may be considered a nuisance in one community may not even show up in another.
Meanwhile, new construction, weather patterns, effective control methods, or any number of other factors can shift mosquito populations around so that one part of a county has a problem one year, and another part the next.
Of course, people tend to call their local mosquito control programs with complaints when they're having trouble with the bloodsuckers, so that's one way for crews to pinpoint the hot spots. Another way is to count mosquitoes in certain areas.
That method is simpler than it sounds. A mosquito control worker goes outside, say near a salt marsh, either early in the morning or right before dark, and lets mosquitoes land on him. The “landing rate” is how many mosquitoes light on him in a minute's time.
Mosquito control officials usually set a certain threshold that will justify breaking out the mosquito spray. For example, in Maryland, crews can spray if the landing rate is one or more mosquitoes per minute in a tested area.
But probably the most common method of mosquito surveillance is the mosquito trap.
The New Jersey Light Trap is pretty much what it sounds like: A light that attracts mosquitoes and a fan that sucks them into a container. Others are similar to the commercial mosquito traps you see on the market for home use, utilizing carbon dioxide or other attractants that mimic the human body.
The idea is to draw in female mosquitoes – males do not bite – so their numbers can be counted and their bodies tested for malaria parasites or viral encephalitis.
Surveillance results also can be used to produce maps that will help mosquito managers locate likely breeding areas that may be ripe for landscaping changes or chemical or biological controls.
Ounce of mosquito prevention vs. pound of cure
Common sense says it's easier to keep mosquitoes from breeding in the first place than it is to hunt down and kill the little suckers once they're flying around.
That's why local mosquito control programs spend so much time on source reduction. The idea is to shrink the number of places the mosquitoes can actually lay and hatch eggs, so that there are fewer created in each cycle.
Every year, about the start of mosquito season, you'll begin seeing the stories in the newspapers and on TV. There will be some county official urging you to clear out all standing water from your backyard, whether that means dumping out buckets, turning over wheelbarrows, or picking up the kids' toys.
They do this because any stagnant water that stands for at least a week or so can become a good spot for mosquitoes to lay eggs that will develop into larvae and, eventually, adults. For the same reason, mosquito control programs will also work with other public agencies to clean up discarded containers such as cans and cut the tall grass on the sides of roads.
Tires are a big one, by the way. Every community tosses out thousands of used tires every year, and they all have to go somewhere. Leave them outside, forgotten, and the insides will collect water and become as good as a swamp for housing mosquitoes.
Aside from clean-up, there is drainage.
Mosquito control checks stormwater systems to make sure the water flows properly and doesn't get backed up anywhere, and also coordinates the digging of ditches that help drain flood-prone land and marshy areas. Lakes and retention ponds are cleared of vegetation and blockages to allow in as much fresh water as possible.
The idea is simple, but it works.
Wiping out the baby mosquitoes
No matter what anyone does, mosquitoes are still going to lay millions of eggs, and they are still going to hatch into mosquito larvae. One way or another, mosquito control programs have to find ways to kill as many of those larvae as they can before the wigglers grow into adults.
A favorite of mosquito control officials is the gambusia, known as the mosquitofish. It is an easy-to-breed North American native about two inches long that feeds mainly on mosquito larvae.
The gambusia are resilient and can live in stagnant water with little oxygen, eating algae if they must, so they are frequently used in swampy or marshy areas and in retention ponds or other small isolated bodies of water.
In a study in New Jersey, just 35 fish released into a stagnant, mosquito-infested swimming pool grew to several hundred fish and completely cleaned out the larvae of two species within a matter of months.
However, mosquito control crews have to be careful where they place the mosquitofish because they are predatory and will eat the young of frogs and other fish.
Meanwhile, some towns in Maine have been working with another mosquito predator since the early '70s.
Each spring, the Chamber of Commerce in Wells, Main, situated near thousands of acres of salt marshes, starts taking orders for dragonfly nymphs – or larvae – from town residents. The developing dragonflies cost about $30 per 50, and people order thousands of them.
The nymphs are released into local freshwater ponds. There, they feed on mosquito larvae, and after developing into adulthood, begin to hunt adult mosquitoes.
While there have been no studies proving the dragonflies are effective, locals swear they have seen major reductions in the mosquito populations, and other nearby towns have adopted are turning to the same method.
But when natural means aren't enough, there are always larvacides.
The most popular is a bacteria used to poison the mosquito larvae, or wigglers. Bacillus thuringiensis israelensis (Bti), grown using fish meal or soy flour as a base, produces proteins that turn into toxins in a larva's stomach.
Bti is made in pellet and liquid form, although pellets seem to be preferred by most mosquito control programs. They can be seeded into a breeding site, such as a pond, or dropped from an aircraft. The bacteria is not harmful to wildlife, fish, or people.
Less favored are larvicidal oils, which are sprayed over the surface of the water. Wigglers must breathe oxygen, so they near the surface and use breathing tubes to breach and draw in air. The oils can either be poisonous, killing the wigglers after being inhaled, or be used simply to suffocate the wigglers by preventing them from reaching oxygen.
Widespread use of mosquito spray
At some point, mosquito control will need to do some selective spraying to kill adult mosquitoes.
They've been tracking nuisance complaints and trapping mosquitoes, so they know where they are worst and when they are out feeding – typically at dawn and dusk.
That's when they will load up the truck, the helicopter, or the airplane and begin dropping insecticide on the areas with the biggest problems. The goal is to put the insecticide into the air, either in a fog or a very light mist, and let it drift through target, killing mosquitoes as it passes and for a few hours after.
One of the most commonly used mosquito insecticides is permethrin, a synthetic form of a natural pesticide made from the chrysanthemum plant. It kills mosquitoes by disrupting their central nervous systems.
Mosquito control officials have to be careful when, where, and how often they use mosquito spray for three reasons.
One, poisons such as permethrin are also toxic to fish, honeybees and other unintended targets. Two, overuse of pesticides has caused some mosquitoes to develop a resistance. And three, the idea of poisons drifting through the air scares people.
However, when mosquitoes are thick, there aren't many other ways to kill them quickly, reducing the number of bites and possible infections. It's a balancing act that mosquito control crews have to do every season.
Put it all together, and that's the way a community practices effective mosquito control – by trying to keep mosquitoes out of the air in the first place, and by attacking them wisely when they're on the move.
Just remember, you have to make sure you take the same approach around your own house, or their efforts, and your tax dollars, go to waste. Plus, you will probably find yourself playing host to some very unwelcome refugees.