| Mosquito Biology for the HomeownerRenee R. Anderson and Laura C. HarringtonIntroductionMosquitoes are flies in the family Culicidae. Over 3,000 known species of mosquitoes exist worldwide. More than 160 species have been documented in North America; at least 62 species occur in New York state. Adult mosquitoes are characterized by having long, slender, needle-like mouthparts (proboscis), antennae, and legs. Their narrow wings are often covered with minute scales. Fine scales cover the mosquito body and vary in coloration from white, silver, or gold, to very dark. Pattern arrangement and scale coloration are often useful for identifying mosquito species. Despite their delicate appearance, mosquitoes are aggravating pests of humans and other animals. Bites from mosquitoes can cause severe discomfort. The resulting intense itching is due to an immunological reaction to mosquito saliva injected into the bite wound. The real danger, however, is that mosquitoes may vector disease organisms. Mosquitoes are capable of transmitting disease-causing viruses, protozoans, and filarial nematodes. The most important mosquito-borne diseases in the United States are caused by viral pathogens and include West Nile fever, eastern equine encephalomyelitis, St. Louis encephalitis, western equine encephalomyelitis, and La Crosse encephalitis. BiologyMosquitoes have four distinct developmental stages: egg, larva, pupa, and adult. Immature stages of mosquitoes require water to complete their life cycle. Mosquitoes are poikilothermic (cold-blooded) animals, thus their rate of development and other aspects of their physiology are temperature-dependent. As the temperature increases, their development time shortens.Eggs
A freshly laid egg is light in color and darkens within a few hours. Mosquito eggs are oval and about 1/40th of an inch (0.635mm) long. Eggs are either deposited singly or as an egg raft depending on the type of mosquito. A standard egg raft is about 1/4 inch (6.35mm) long and contains 100-200 eggs. Some species of mosquitoes lay their eggs singly and deposit them directly on water or floating aquatic vegetation. Others will lay their eggs on moist soil that is subject to periodic flooding, or above the water line in natural and artificial containers. The number of single eggs laid per batch varies within and between mosquito species and can range from 60 to 200. LarvaeLarvae will emerge from eggs within 2-3 days when environmental conditions are ideal. All mosquito larvae go through four developmental stages called instars. First instars are barely noticeable to the human eye. Last larval instars of some species can be approximately 1/2 inch (12.7mm) long. Larvae move through the water in a serpentine motion. When they sense a shadow or movement in their habitat, larvae will quickly dive to the bottom to avoid the source of disturbance. One first (upper right) and two fourth instar larvae of Oc. j. japonicus. The scale to the left side is in millimeters.Larvae have a well-formed head and lack legs. Upon careful inspection one can distinguish the wider thorax from the long and slender abdomen. A tube-like structure, called a siphon, is located at the tip of the abdomen. Larvae use the siphon to breathe air from the water surface. Larvae possessing a siphon (Culicine) hold their body roughly at a 45-degree angle from the surface. Species of mosquitoes lacking a respiratory siphon (Anopheline) hold their body horizontal to the water surface. They obtain air through openings located on the dorsal surface of the abdomen. A few species will bore their siphon into stems of aquatic plants to obtain oxygen.  Anopheles punctipennis larva; note the absence of a siphon. The scale to the left side is in millimeters.Mosquito larvae can be found in a wide variety of habitats, including temporary floodwater and snowmelt pools; more permanent water habitats like marshes, swamps, lagoons, and ponds; stagnant waters; and natural and artificial containers. Shallow water is ideal for larval survival because there is less turbulance and wave action. Upper water movement interferes with the surface feeding of some mosquito species, and in most species, it hinders the larvae and pupae from obtaining oxygen at the air-water interface. A deep-water environment prevents bottom-feeding water from reaching food that has accumulated at the lower levels of the water column. Water quality in larval habitats can vary from fresh to saline to high in organic wastes. Different species can tolerate and thrive in water with varying degrees of organic content. Mosquito larvae eat a variety of dead and living organisms, including detritus, algae, bacteria, and fungi. Some mosquito species are predaceous and feed on other mosquito larvae and small invertebrates. Depending on water temperature, crowding, and food availability, the larval stage is typically completed in 5-6 days.5,7 PupaeMosquito pupae are active when compared to other insect pupae. Pupae move in a somersault fashion through the water. Pupae breathe through tubes located on the thorax and will remain at the water surface unless they are disturbed. This non-feeding stage can be completed in as few as 2-3 days.5,7AdultsBoth male and female mosquitoes feed on sugar sources such as plant nectar and honey dew, but only females feed on blood. Female mosquitoes use proteins and lipids from the blood meal to develop a batch of eggs. There are a few exceptions to this rule. Some species are autogenous, meaning a female is able to utilize energy reserves from the larval stage to produce eggs without a blood meal.Many species of mosquitoes are specific in their host preference for birds, mammals, or cold-blooded vertebrates such as reptiles and frogs. Consequently, various mosquito species use a wide variety of cues to find a suitable host, often involving a variety of complex interactions. This complex of cues is still not fully understood by scientists. These cues can be either odors emanating from skin or breath, or visual cues such as movement or contrast of a potential host with the surrounding background. Carbon dioxide is a major cue and is often used as bait in mosquito traps. Several hundred compounds found in human breath, secretions, and sweat glands have been identified and vary in their degree of attractiveness to female mosquitoes.6 Some of the more attractive odors include: carbon dioxide, alanine, lysine, lactic acid, and estrogen. Some chemicals emanating from a potential host may be more important for certain species of mosquitoes. In other mosquito species, these very same odors may play a secondary role, no role, or act to repel mosquitoes.6 The distance that mosquitoes can fly is difficult to generalize because mosquito species vary in their flight range. Some species can fly long distances (up to 10 km), but most do not travel more than several yards.6,7,15 ManagementNew York state has specific environmental laws, rules, regulations, and policies relating to mosquito control and management. Area-wide control of adult mosquitoes and control of mosquito larvae and pupae in wetlands, waterways, catch basins, and public areas fall under these regulations and cannot be performed by the general public. Integrated Pest Management (IPM) uses a strategic approach to controlling mosquitoes. IPM is most likely to be effective when several techniques are used together. The following mosquito IPM recommendations are applicable to homeowners and include measures you can take only with your own property.LarvaeSource ReductionAn effective, long-term method of minimizing mosquito problems is reducing or eliminating potential breeding sites around the home. Water is necessary for mosquito development. Containers of all types can hold water and potentially serve as larval habitat for certain peridomestic species. Properly dispose of old tires, cans, bottles, water-collecting rubbish, and other unused or unwanted containers. Eliminate standing pools of water created from tire ruts or similar sites that hold water for more than one week. Avoid excess watering of lawns and gardens. Control seepage from air-conditioning units and ill-fitting garden hoses.
Periodically clean birdbaths, pet dishes, plant pots, rain barrels, and kiddie pools and monitor them for mosquito production. Keep an eye out for small black mosquito eggs pasted around the rim of these containers or black egg rafts floating on water. When cleaning containers, be sure to thoroughly scrub the sides in order to dislodge any attached eggs. Survey your yard for mosquito larvae in other types of water-holding containers such as tree holes, ornamental ponds, and clogged rain gutters. PredatorsMosquito larvae confined to containers, ornamental ponds, or small temporary pools may be controlled in certain situations by biological predators (although the efficacy of this approach has not been fully investigated by scientists). Larvae-eating fish, immature dragonflies and damselflies, aquatic beetles, cannibal mosquito larvae, and certain aquatic planaria, type of flatworm, will feed on mosquito larvae and may help reduce larvae in breeding sites if initial larval numbers are not high. Consider encouraging the establishment or conservation of these predators. Distributors of some of these predators may be found on the Internet. Stocking of mosquito-eating fish requires a special permit from the New York State Department of Environmental Conservation.LarvacidesLarvicides are products that kill mosquito larvae. Targeting larvae is more desirable than controlling adults because the larvae are concentrated in a relatively small area. Products containing Bacillus thuringiensis variety israelensis (Bti, a microbial compound) and methoprene (an insect growth regulator) are currently available over-the-counter for homeowner use in New York state. Advantages of these compounds are their specific action against insects and minimal impact on nontarget organisms such as fish and other aquatic animals.The microbial insecticide, Bacillus thuringiensis variety israelensis, needs to be consumed by mosquito larvae and must be applied well before the last larval instar (stage). Its effectiveness depends upon the mosquito species present, water quality, and size of the initial larval population. The product is made from a dormant spore of a soil-inhabiting bacterium. Ingestion of the spore disrupts the gut wall of larvae, causing death. According to the Environmental Protection Agency, Bacillus thuringiensis variety israelensis does not pose risks to wildlife, non-target species, or the environment.18 Mosquito larvae in water treated with the insect growth regulator methoprene continue to feed and grow normally until the pupal stage. Exposure of larvae to methoprene disrupts normal molting into the pupa and results in death. The Environmental Protection Agency states that methoprene toxicity to fish and birds is low, and methoprene is nontoxic to honeybees.18 AdultsPhysical ExclusionAn often overlooked but highly effective means of controlling mosquitoes is the use of tight-fitting and well-maintained window and door screens with a 16-inch mesh. Make sure there are no holes in screens, because mosquitoes can easily find these and enter your home. Also make sure there are no gaps between the screen and window frame. Be sure to calk and seal all cracks around windows. Some mosquito species are attracted to outdoor lights. Reduce unnecessary lighting, or move the lights away from sensitive areas such as doorways. Replace outdoor lights with yellow bug lights. Bug lights are less attractive to many kinds of insects and can be found wherever household light bulbs are sold.AdulticidesAdulticides are substances that kill adult mosquitoes. Yard foggers or sprays are available to homeowners for temporary control of adults in the yard. These products contain various formulations of chemical insecticides such as pyrethrin, malathion, or permethrin. These products may only result in temporary control of mosquitoes and should only be considered as a last resort. The duration of their activity depends on the method of application and environmental conditions such as rain, sunlight, and high temperature. Furthermore, they are much more toxic to humans, pets, and other animals than the larvicidal compounds. Read and follow directions on the label; remember, it is the law when applying pesticides.Personal ProtectionYou can take individual measures to minimize your exposure to mosquito bites. If possible, modify your routine or other outdoor activities to minimize your time outdoors during peak mosquito activity. Predicting "peak mosquito activity" is difficult because it varies locally and seasonally, and it depends on the mosquito species present in your area. Many species are active during early evening hours. Some mosquitoes are active during night, while others will readily bite during daylight hours. There also seems to be a difference in individual human attraction to mosquitoes. Be sure to pay attention to the biting pressure your children may receive while they are outside playing. Wear protective clothing such as long sleeve shirts, long pants, socks and shoes. Consider using an insect repellent while outdoors to reduce your chances of being bitten. If you use a repellent, make sure you read and understand the label prior to each use. Some repellent formulations can be applied only to skin, on both skin and clothing, or only on clothing! Insect repellents come in a variety of formulations: aerosol sprays, pump sprays, lotions, liquids, and with sunscreen. Common ingredients found in over-the-counter repellents belong to two broad categories: synthetic chemicals and biopesticides.Synthetic RepellantsTwo common synthetic repellents have DEET (N,N-Diethyl-m-toluamide) or permethrin as active ingredients. DEET can be applied directly to the skin or clothing. However, DEET can damage some types of fabrics, watch faces, and painted and varnished surfaces. DEET cannot be applied to skin that is covered with clothing. The United States Environmental Protection Agency (EPA) has completed an extensive reevaluation of DEET and has "concluded that as long as consumers follow label directions and take proper precautions, insect repellents containing DEET do not present a health concern."19 Overall, studies have shown that higher concentrations of DEET are correlated with a greater length of protection but products containing lower concentrations of DEET in the 15-25% range afford good protection.2,3,8,9 The length of protection provided will depend on various conditions such as how much you sweat, environmental temperature, and mosquito species present. Starved mosquitoes are not as easily deterred by DEET.20 Do not overuse products containing DEET, and be sure to wash treated skin with soap and water upon returning indoors. The American Academy of Pediatrics (AAP),1 the Environmental Protection Agency (EPA),17 and the National Pesticide Information Center (NPIC)14 provide additional information on DEET. The Internet address for these organizations can be found in the reference section. Persons concerned with using DEET-based products on their children should contact their health care provider.Permethrin (0.5% active ingredient) cannot be applied directly to the skin. It is applied to clothing and dried before the clothes are worn. The advantage of permethrin is that it is a toxicant and will kill any mosquitoes landing on treated clothing. Biopesticide RepellantsThere are non-DEET and non-permethrin repellents labeled for use against mosquitoes; however most biopesticide repellents do not provide the same degree of complete protection as synthetic repellents.2,3 A laboratory based study found that protection afforded by a soybean oil repellent (2% active ingredient) was not significally different from the complete protection time of a product with a low concentration of DEET (4.75% active ingredient).9 The range of complete protection for the 2% soybean repllent was 16-195 minutes while the 4.75% DEET product provided 45-120 minutes of protection. Active ingredients of other biopesticide repellent products include: oil of citronella, oil of eucalyptus (p-menthane-3, diol), and IR3535 (found in products sold through catalog cosmetic distributors).Other Management MeasuresContrary to popular belief, bug zappers do very little in controlling adult mosquitoes. Studies have shown that far more beneficial insects are killed by bug zappers than are pest species.10 There is evidence from at least one backyard study that electric bug zappers increased the number of female mosquitoes present in the yards as opposed to yards without the devices, and were not effective in reducing the number of female mosquitoes landing on people.13,16 Similar results were found with electronic mosquito repellers. Persons using the devices recovered more female mosquitoes landing on them when compared to those not using them.11 The repellers did not afford any protection against bites.11Scientific studies to date have demonstrated that propane-powered mosquito traps do collect adult mosquitoes.4,12 However, no studies exist that document the efficacy of these types of traps in significantly reducing mosquito populations to the level that they prevent bites, or decrease the risk of contracting a mosquito-borne disease. Please contact your local Cornell Cooperative Extension office for current chemical control recommendations for mosquito larvae and adults. Remember, the label is the law. Contact the New York state Department of Environmental Conservation for any regulations that may apply to your particular situation. References
This publication contains pesticide recommendations. Changes in pesticide regulations occur constantly and human errors are still possible. Some materials mentioned may no longer be available and some uses may no longer be legal. All pesticides distributed, sold or applied in New York State must be registered with the New York State Department of Environmental Conservation (DEC). Questions concerning the legality and/or registration status for pesticide use in New York State should be directed to the appropriate Cornell Cooperative Extension Specialist or your regional DEC office. READ THE LABEL BEFORE APPLYING ANY PESTICIDE. | Interesting Facts
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Clustering of Oc. j. japonicus eggs on the inside rim of a plant pot.
A mosquito pupa. The scale to the left side is in millimeters.
Female Ochlerotatus j. japonicus blood feeding.
Torn window screens can easily allow mosquitoes to enter your home.