Why do mosquitoes bite?
Only female mosquitoes bite or take a "blood meal." The blood is necessary for the development of her eggs.
Typically, both male and female mosquitoes feed on plant nectar. The plant sugars provide energy for the mosquito. After the male mates with the female mosquito, eggs will begin to grow in her abdomen. For most species, it is crucial she take a "blood meal" from an animal. The protein from the blood causes the eggs to develop properly.
Mosquito management is a multi-disciplinary subject that combines the art of understanding mosquito behavior with the science of knowing how to locate and control mosquito populations. The Lake County Mosquito Management Section manages mosquitoes and other biting arthropods of public health importance in order to reduce the risk of arboviral disease transmission and to ensure a reasonable quality of life for all residents and visitors of Lake County.
Adult Mosquito Activity
All mosquito species have their own specific behavioral patterns that influence activity. However, environmental factors seem to have a more dramatic effect on mosquito activity.
Studies have shown that the majority of mosquito activity occurs at night with over half of this activity occurring during the crepuscular periods. Also, one study showed that up to five times as many mosquitoes are in flight during a "full moon" when compared to a "new moon". Only a few mosquito species are active during the daylight hours.
Temperature plays an important role in mosquito activity. At 68°F mosquitoes in flight begin to decrease and are almost nonexistent at 50°F. Relative humidity also has an effect on mosquito activity. A burst of activity occurs when the humidity reaches 90% and peaks during light showers. However, mosquitoes seek shelter during heavy rain and are rarely in flight.
Adult Mosquito Surveillance
A countywide adult mosquito surveillance program is conducted year-round in Lake County. Mosquito surveillance can be defined as a means of determining when and where mosquitoes are active and breeding. Lake County Mosquito Management deploys a series of New Jersey Light Traps, Miniature CDC Light Traps, and BG-Sentinel Traps at various locations throughout the County to determine the fluctuation in adult mosquito populations.
New Jersey Light Trap
Lake County is divided into 10 spray regions and 4 New Jersey Light Traps are randomly located at permanent sites in each of the regions to avoid any bias in the collection data. Based upon surveillance analysis and inspections, adult mosquito spray operations can be justified in order to meet current state and federal regulations governing the application of pesticides.
Trap samples are collected twice a week and the samples are counted and identified to species. Known mosquito-breeding sites are surveyed periodically to document trends in mosquito production. The intent of this surveillance program is not to monitor mosquito populations at any given trap site but, rather, to determine fluctuations in mosquito population levels compared to an established baseline for each spray region.
Mosquito Spray Truck
Adulticiding is defined as a process for safely and efficiently dispersing insecticides to control adult mosquitoes. It can be performed by truck for localized ground applications or by aircraft for broad aerial applications. Lake County's Mosquito Management Section primarily uses mosquito spray trucks to manage adult mosquito populations. Spray truck missions usually commence in April and end in December operating Monday through Friday from dusk to midnight. Spray Truck Operators are assigned to one or more of the 10 spray regions each night based on surveillance analysis and service requests. Aircraft treatments may be used during times of a mosquito-borne epidemic or high infestations of pestiferous mosquitoes.
There are various chemicals approved by the State of Florida for the use for mosquito adulticiding. The two most often used by Lake County are Malathion (Fyfanon) and Permethrin (Permanone 31-66). Malathion is applied as a straight formulation and Permethrin is mixed with a diluent at a 4 to 1 ratio.
Mosquito Inspection and Larviciding
Mosquito larviciding is an activity that incorporates biological and chemical control of immature mosquitoes. This can range from simply dumping a pale of water to applying larvicides. Mosquito larvae and pupae are searched for and managed to help in reducing the emerging adult mosquito populations at the source. Three full-time field operations personnel and one entomologist search for possible mosquito breeding sites in assigned areas of the County and, if larvae are found, apply chemical and/or biological control methods.
Biological control, or biocontrol, involves the use of predator fish, insects, or pathogens to control immature mosquitoes. Lake County's mosquito management personnel primarily use predator fish, such as Gambusia, Fundulus, and Poecilia species, for biocontrol. These fish can be found in most permanent pools of water and are collected by net. The fish are placed in an aerated container for transport to the breeding site. Also, these fish are kept in fish rearing tanks located at the Mosquito Management facilities.
Chemical control involves the application of larvicides to reduce the numbers of immature mosquitoes. Some of the more common mosquito larvicides used are the naturally occurring Bacillus thurngiensis israelensis (Bti – VectoBac 12AS), Bacillus sphaericus (Bsph - FourStar CRG), monomolecular surface oils, and spinosad (Natular 2EC, Natular G30).
Mosquito Management staff investigate service requests made by the public to determine the scope of the mosquito problem and the appropriate integrated pest management (IPM) measures to be taken. Public awareness and education on eliminating mosquito-breeding sources are a primary goal of the program.
Mosquitoes and Aquatic Plants
a) The three most important mosquito species that utilize aquatic plants as a primary habitat for egg deposition and larval development are Mansonia dyari, Mansonia titillans, and Coquillettidia perturbans.
If adult Mansonia species are discovered through routine surveillance monitoring, a thorough survey of the immediate area is conducted to locate fresh water sources containing water hyacinths and water lettuce. If a suspected fresh water source is found, a larval survey is conducted. Mansonia mosquitoes attach to the root structures of floating aquatic plants. If disturbed, the larvae will immediately release and fall to the bottom.
Coquillettidia perturbans can travel several miles. Therefore, a more widespread survey of fresh water sources containing cattails, sedges, aquatic grasses, or arrowhead may have to be done. The eggs and larvae of this mosquito are usually found in the detritus material at the base of the aquatic plants.
Because aquatic plants can, at times, produce heavily vegetated stands, the use of conventional mosquito management techniques may be ineffective. Predator fish are usually not effective because of the dense vegetation. Monomolecular oils do not work because the immature mosquitoes are located below the water surface. Bti may be effective if the product is applied directly to the infested areas. This may be difficult and labor intensive if the aquatic vegetation is dense. Eradication or maintenance level control of the aquatic plants is the best method of managing these mosquitoes.
What is Saint Louis Encephalitis?
Saint Louis Encephalitis (SLE) is a mosquito-transmitted viral disease. It was first recognized in St. Louis in 1933. Epidemics occur sporadically throughout the United States. During an epidemic, several hundred people may become ill, sometimes fatally. Symptoms of SLE are similar to other viral infections and may include high fever, nausea, severe headaches and tiredness.
The severity of the symptoms varies from person to person. They range from no symptoms at all to mild flu-like symptoms to severe flu-like symptoms — and even death. Only one in 200 people who become infected with SLE virus will develop the disease. The likelihood of developing SLE symptoms is generally higher for older people.
Only a few species of mosquito in a particular area are generally capable of transmitting SLE. Mosquitoes pick up the virus in the blood of wild birds carrying the disease. The birds are usually not sick themselves. The virus incubates in the mosquito's body and eventually migrates to the mosquito's salivary glands. This process takes about two weeks. If a particular type of mosquito bites a SLE-infected animal and two weeks later bites a person, SLE transmission may occur and that person may or may not go on to develop encephalitis.
In Florida, the species of mosquito that is most often responsible for SLE transmission is Culex nigripalpus, which breeds in many sites.
West Nile Virus
The West Nile Virus is a mosquito-transmitted virus that can cause encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord). It can even cause permanent neurological damage or be fatal. Several mosquito species transmit West Nile Virus, but they must first get the virus from an infected source. Many species of birds, especially crows and blue jays, have been found to harbor West Nile Virus. There is no specific treatment for West Nile Virus and there is no vaccine to fight it. Therefore, prevention is the best cure. It all comes down to not being bitten by mosquitoes. Stay indoors at dawn, dusk and in the early evening when mosquitoes are most active.
However, if residents must venture outside: Wear long-sleeved shirts and long pants when outside, spray clothing with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing and apply insect repellent sparingly to exposed skin.
The American Pediatric Society recommends no greater than 10 percent DEET be applied to children. When using an insecticide or repellent, be sure to read and follow the manufacturer's directions for use as printed on the product. For more information about West Nile Virus or any other mosquito transmitted diseases, call the Lake County Mosquito Control office at (352) 343-9419.