The objective of mosquito management is to keep populations below levels where they become a nuisance or a public health problem leading to an outbreak of disease. Mosquito management often occurs on an areawide basis by public agencies that either are part of local health departments or are independent districts organized specifically for mosquito control. California has more than 60 mosquito and vector control districts. Some are small and have responsibility for mosquito abatement in a few hundred square miles, while the activities of others can encompass one or two entire counties.
Vector control technicians search out mosquito larvae in standing water and use appropriate control measures that are cost-effective and environmentally friendly. Control measures include environmental manipulation to reduce aquatic habitats such as removing dense patches of decaying vegetation conducive to mosquito production, applying mosquito-specific control agents, and stocking fish that feed on the larvae. Many materials currently in use are biological in origin and are highly specific for mosquitoes while having little or no effect on other organisms.
Controlling irrigation water in agricultural areas to avoid excess runoff also is an important mosquito control method. However, eliminating natural bodies of water such as vernal pools that also serve as wildlife habitat has ceased to be a mosquito control option because of habitat preservation concerns.
Occasionally mosquito abatement agencies also might have to use chemical pesticides to kill adult mosquitoes, but ordinarily this occurs only when adult populations become so large they cause extreme annoyance to many people or when the threat to people of an outbreak of a disease-causing pathogen is high.
In many areas of California, public mosquito and vector control agencies keep mosquito numbers down to tolerable levels all or most of the time. However, some Californians live in areas where no organized mosquito control exists. These usually are low-density areas in foothill, mountain, or desert regions.
People living in these areas or in other locations where mosquito populations become bothersome can protect themselves from mosquitoes by using a variety of strategies. These include keeping fine mesh screens on windows and doors in good repair, draining standing water or treating it with the microbial control agent Bacillus thuringiensis subspecies israelensis (Bti), incorporating mosquito-eating fish, and wearing repellents and protective clothing when outdoors during the mosquito season.
The most effective control methods are those targeted against the larval stage of the life cycle. If you have an area or object that can hold water for more than a few days, drain it or fill it with soil or cement, treat it with Bti, or stock it with mosquito-eating fish. Even small containers such as soda cans, glass jars, flower pot saucers, or tree holes can provide a habitat for mosquito development.
Keep in mind adult mosquitoes can fly several miles from where they develop. Even successful control of mosquito larvae on your premises might not result in eliminating mosquito numbers or biting activity. See Table 1 for ways to reduce mosquito populations in a given situation.
Mosquito-eating fish can be an important control agent for immature mosquitoes. People worldwide have used the mosquitofish, Gambusia affinis, for mosquito control. These fish are most effective in man-made bodies of water that don’t connect with natural waters and don’t contain dense stands of emergent vegetation. You can obtain mosquitofish from most vector control districts.
You never should release mosquitofish into streams, ponds, and lakes, because these fish aren’t native to California. Fish native to California are being considered for use as mosquito control agents in habitats where mosquitofish no longer can be released. Your local vector control district is a good source of additional information for mosquitofish alternatives.
Using insecticide sprays or outdoor foggers for controlling adult mosquitoes has limitations. While they can provide a temporary reduction of the adult population—which can be useful if you make the application shortly before a backyard picnic or family gathering—alternative, more long-term approaches for controlling mosquitoes are preferable. Equipment for applying outdoor sprays is expensive and complex.
Probably the most effective method of personal protection from mosquito bites is to avoid places where their densities are high and avoid being outside when mosquito activity is at its highest. In mountainous areas, most mosquito species bite during morning and afternoon hours and often not at all when it is dark. In some low-elevation areas, such as the Central Valley, some mosquitoes tend to bite at night, while others bite during the day.
If you find yourself in a situation where you can’t avoid mosquitoes, first minimize the amount of exposed skin surface by wearing a hat or head net, long trousers, and a long-sleeved shirt. Some mosquitoes will bite through lightweight clothing, but the number of bites you receive will decrease if you cover most areas of your body.
Research has shown that the effectiveness of most other products marketed to repel mosquitoes differs appreciably. Wristbands that contain an aromatic repellent, ultrasonic emitters, electric grids, electronic repellers, aromatic plants (the most common one is the so-called mosquito plant, Pelargonium x citrosum), incense coils, vitamin B1, and mixtures of brewer’s yeast and garlic are ineffective.
Oil of citronella, which is extracted from Andropogon nardus, has a reputation for repelling mosquitoes. Burning citronella candles or mosquito coils containing allethrin works best if there is relatively little air movement, but these products are for use only outdoors.
Electric bug zappers used to kill pest insects probably are counterproductive, because many of the insects these traps kill are those that prey on mosquitoes. Manufacturers claim that clip-on, battery-operated dispensers for the pyrethroid pesticide metofluthrin repel mosquitoes for up to 12 hours per refill, but like most repellents, effectiveness varies among users.
You can trap mosquitoes using products such as the Mosquito Magnet, which releases attractants such as carbon dioxide. However, you’ll want to weigh the cost of the trap and its operation against the fact that although the trap attracts mosquitoes searching for a host to feed on, if captures only a small proportion of the attracted insects. Also a single trap might not be effective enough for controlling adult mosquitoes, which often disperse across a broad geographic area.