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As the weather warms and outdoor activities increase, people are becoming increasingly annoyed and concerned with the number of mosquitoes invading their airspace. Almost everyone has had the unpleasant experience of being bitten by a mosquito. Mosquito bites can cause severe skin irritation through an allergic reaction to the mosquito's saliva causing a red bump and itching. But a more serious consequence of some mosquito bites may be the transmission of certain diseases such as malaria, dengue fever, encephalitis, and of course, West Nile Virus. Not only can mosquitoes carry diseases that infect humans, but they also can transmit diseases and parasites to animals, such as dogs and horses. These include dog heartworms and eastern equine encephalitis.
Controlling mosquitoes has become more involved than a mere slap on the wrist, or leg, or neck or other part of the body. Today, communities are getting involved with citywide spray programs, and homeowners are spending thousands of dollars for special equipment to keep them safe from mosquito’s harm. But, there is more to controlling mosquitoes than just using foggers, repellents and smoke screens. To effectively control mosquito populations, a control program needs to be developed.
Mosquito control practices are based upon the biology and behavior of two different mosquito species. The first control practice involves the mosquito species that lay their eggs in masses or rafts on the water's surface. Some of these species, which are found throughout the U.S., often lay their eggs in natural or artificial water-holding containers found around the home or in naturally occurring pools. The second type of mosquito species involves mosquitoes that lay their eggs on moist soil or other areas that will be flooded with water at a later time. After about two days, these eggs are ready to hatch, but not until flooded with water. These eggs can withstand dry conditions for months. In inland areas of the U.S. where these mosquitoes breed, heavy rains and flooding can produce millions of mosquitoes in a short time. Similar situations occur along coastal areas where mosquitoes have adapted to salt marsh habitats. Some salt marsh mosquitoes are strong fliers and can travel up to 50 miles from the breeding site.
Mosquito Life Cycle
Approximately 200 species of mosquitoes breed in the United States, all of which live in specific habitats, exhibit unique behaviors and bite different types of animals. The life cycle of all mosquitoes consists of four distinct life stages: egg, larva, pupa and adult. The first three stages occur in the water, while the fourth stage, the flying, biting adult, occurs out of the water and is the stage that alarms most people. The male mosquito lives a very short time, while the female may live for several weeks. It is the female mosquito that bites to draw blood from humans and/or animals to feed her developing eggs. She then, depending on the species, lays her eggs in standing water or marshy areas.
The type of standing water in which the mosquito chooses to lay her eggs depends upon the species. The presence of beneficial predators such as fish and dragonfly nymphs in permanent ponds, lakes and streams usually keep these bodies of water relatively free of mosquito larvae. However, temporary pools and puddles are all prolific mosquito-breeding sites. Clogged ditches, tree holes and containers, such as old tires, buckets, toys, empty flower pots, or tarpaulins, are prolific breeding sites for some of the most annoying and potentially dangerous mosquito species, such as the Asian tiger mosquito.
West Nile Virus History and Information
The West Nile virus was first discovered in a woman from the West Nile District of Uganda in 1937. The disease spread throughout Africa, Eastern Europe, West Asia, and the Middle East, eventually appearing in the Eastern United States in 1999. Due to the concern for public health, the Center for Disease Control and Prevention and affected states developed and implemented surveillance and response plans. As a result, targeted pesticide applications were performed to control adult mosquitoes that transmit the virus.
Surveillance practices include the use of sentinel chickens, human and veterinary monitoring, and mosquito collection. Some adult mosquitoes carrying the virus have been determined to survive over the winter. Therefore, in addition to efforts to control mosquito larvae, mosquito control programs in many areas implemented targeted pesticide applications to control adult mosquitoes.
Symptoms of West Nile Virus in humans generally appear within 3-6 days of infection and are typically flu-like, including a mild fever, headache, body ache, skin rash and swollen lymph glands. Some individuals who become infected with the disease (less than 1%) develop encephalitis, which is an inflammation of the brain. West Nile Virus encephalitis primarily affects persons over 50 years of age and those with a compromised immune system. The rate of fatality is 3-15% among those who develop the disease. Currently no vaccine is available for West Nile Virus.
Other Diseases Transmitted by Mosquitoes
The diseases that may be transmitted by mosquitoes include mosquito-borne viral encephalitis, dengue, yellow fever, and malaria. Most of these diseases have been prominent in the United States in the past, but today, only the insect-borne encephalitis occurs annually and dengue occurs only periodically. Human cases of encephalitis range from mild to severe illnesses that can be fatal. Dengue usually is an acute, nonfatal disease, characterized by sudden onset of fever, headache, backache, joint pains, nausea, and vomiting. Some cases will progress to dengue hemorrhagic fever, characterized by severe rash, nosebleeds, gastrointestinal bleeding and circulatory failure that can result in dengue shock syndrome and even death. Recently, dengue has occurred with increasing frequency in Texas. Other pathogens transmitted by mosquitoes include a parasite that causes malaria, and Dirofilaria immitis, a parasitic roundworm that causes heartworm in dogs.
Control of Mosquitoes
Mosquito control programs put high priority on larvae control, eliminating the need for additional control procedures on the adult population. Since mosquitoes must have water to breed, methods of prevention may include controlling water levels in lakes, marshes, ditches, as well as stocking bodies of water with fish species that feed on larvae. Both chemical and biological measures may be employed to kill immature mosquitoes during larval stages. Larvicides target larvae in the breeding habitat before they can mature into adult mosquitoes and disperse. Larvicides include the bacterial insecticides, Bacillus thuringiensis israelensis, and the insect growth inhibitor, methoprene. Mineral oils and other materials can also be used to form a thin film on the surface of the water, which cause larvae and pupae to drown.
Adult mosquito control is often used by communities to combat a very large infestation. Pesticides registered for this use are applied either by aircraft or truck-mounted sprayers. However, controlling mosquito larvae before they emerge as adults can reduce or eliminate the need for ground or aerial application of pesticides to kill adult mosquitoes.
By far, the most important step in mosquito control is to eliminate potential breeding habitats for mosquitoes. Get rid of any standing water around the home, including water in flower pots, garbage cans, old tires, gutters, ditches, wheelbarrows, bird baths, hollow trees, and wading pools. Any standing water should be drained, including abandoned or unused swimming pools. Mosquitoes can breed in any puddle that lasts more than 4 days. For personal protection, wear headnets, long-sleeved shirts, and long pants if venturing into areas with high mosquito populations, such as salt marshes or wooded areas. Use mosquito repellents when necessary, always following label instructions.
Bacillus thuringiensis israelensis
Bacillus thuringiensis israelensis (BTI) is a naturally occurring soil bacterium registered for control of mosquito larvae. The EPA first registered BTI as an insecticide in 1983. Mosquito larvae eat the BTI product that is made up of the dormant spore form of the bacterium and an associated pure toxin. The toxin disrupts the gut in the mosquito by binding to receptor cells present in insects, but not in mammals. LESCO offers Mosquito Dunks (#035170) which contains BTI. Each dunk treats 25 to 100 square feet of surface water.
Methoprene
Methoprene is a compound first registered by the EPA in 1975 that mimics the action of an insect growth-regulating hormone and prevents the normal maturation of insect larvae. It is applied to water to kill mosquito larvae, and it may be used along with other mosquito control measures in an IPM program. Methoprene, used for mosquito control according to its label directions, does not pose unreasonable risks to humans, wildlife or the environment. In addition to posing low toxicity to mammals, there is little opportunity for human exposure, since the material is applied directly to ditches, ponds, marshes, or flooded areas that are not drinking water sources. Toxicity of methoprene to birds and fish is low, and it is nontoxic to bees. Methoprene breaks down quickly in water and soil and will not leach into ground water. Methoprene mosquito control products present minimal risks to freshwater fish, freshwater invertebrates, and estuarine species. The methoprene-containing product, Pre-Strike (#084144), is available from LESCO in 1 pound containers that will treat 8,700 square feet.
Synthetic Pyrethroids
Pyrethroids are synthetic chemical insecticides that act in a similar manner to pyrethrins, which are derived from chrysanthemum flowers. Bifenthrin (Talstarâ), lambda-cyhalothrin (Demandâ CS) and beta-cyfluthrin (Tempo) are synthetic pyrethroids commonly used in mosquito control programs to kill adult mosquitoes.
Most pyrethroid mosquito-control products that are used by public health officials and trained personnel are applied as an ultra low volume (ULV) spray. ULV sprayers dispense very fine aerosol droplets that stay aloft and kill adult mosquitoes on contact. Pyrethroids used in mosquito control are typically mixed with a synergist compound, such as piperonyl butoxide, available from LESCO as the product, Kicker (#033716), which enhances the effectiveness of the pyrethroid compound.
Pyrethroids can be used for public health mosquito control programs without posing unreasonable risks to human health when applied according to the label. Pyrethroids are low in toxicity to mammals, and are practically nontoxic to birds. However, pyrethroids are toxic to fish and to bees. For that reason, the EPA has established specific precautions on the label to reduce such risks, including restrictions that prohibit the direct application of products to open water.
Additional Information
For additional information on the West Nile Virus, including updates, frequently asked questions, avoidance steps, press releases, transmission cycle and other pertinent information regarding mosquitoes and the diseases they could possibly transmit, visit the websites listed below.
If you need specific product information please contact LESCO Agronomic
Technical Services at (800) 321-5325 ext. 6150 or email at techguys@lesco.com.
LESCO is a registered trademark of LESCO Technologies, LLC.
Pre-Strike is a trademark of Wellmark International. Talstar is a registered
trademark of FMC Corporation. Demand is a registered trademark of Syngenta Group Company. Tempo is a registered trademark of Bayer Corporation. Kicker is a registered trademark of Aventis. Mosquito Dunks is a registered trademark of
Summit
Chemical Company. | |