Life history and habits

Adult mosquitoes are terrestrial and can fly long distances. They begin mating several days after reaching adulthood. Mosquitoes feed on flower nectar, fruit juice, and female mosquitoes feed on the blood of vertebrates which is necessary for egg development. The females of some species, such as Culex spp. prefer feeding on the blood of birds, which has important implication in human health since birds are reservoir hosts of WNV. Female mosquitoes are attracted to carbon dioxide and compounds in sweat, and most actively search for a blood meal during the evening hours beginning just before sundown until two to three hours after dark. Eggs develop three to five days after the female engorges on a blood meal, at which point the gravid females begin searching for suitable breeding sites. Female mosquitoes only mate once and typically produce one to three batches of eggs before dying.

Eggs are laid singly or in floating masses, called rafts, in aquatic or very damp terrestrial environments. Eggs typically hatch in 1-3 days, though the exact incubation period depends on the species of mosquito and environmental conditions. The eggs of some species are laid in moist soil or other wet substrates and do not hatch until submerged by rising water during periods of rain or snowmelt in the spring. In some instances, the eggs may not hatch until a year or more after being laid. In urban areas, egg-laying sites include storm sewers, clogged drains, gutters, play equipment, tires, mud puddles, and other bodies of still water. In natural ecosystems, mosquitoes breed in marshes, streamside pools that form during spring floods, irrigated agricultural areas, wetlands, and tree hole cavities.

The larvae develop through four instars and increase in size with each molt. The larvae actively feed on organic matter and most species obtain oxygen from the atmosphere via a breathing tube at the end of the abdomen. When disturbed, they can be observed swimming to the bottom of the water body to escape potential danger. Mosquito pupae do not feed and unlike most insects, they are very active and must periodically swim to the water surface for gas-exchange. The pupal stage lasts for several days, and adults emerge from the puparium at the water surface.

Bites

Mosquitoes feed by piercing the skin with a proboscis and sucking blood. While feeding, mosquitoes inject saliva into the skin, which causes the formation of an itchy bump. Individuals differ in their reaction to mosquito bites, with some people having mild reactions, while others experience a large area of swelling, soreness, and redness.

Bumps tend to appear a few minutes after the bite was inflicted. The bump can occur on any exposed area of skin and is most often red or brown. Multiple bites can appear in one day. In addition to causing discomfort, mosquitoes can transmit several human pathogens, most notably WNV.

West Nile virus (WNV)

Mosquitoes are the primary vector of WNV, which is a human pathogen that attacks the nervous system and causes West Nile fever and encephalitis. No vaccine is available for this virus, which was introduced to the Western Hemisphere in 1999. In the western United States, C. tarsalis is primary vector of WNV. The pathogen is transmitted between mosquitoes and animal hosts, and birds are the predominant reservoir of the virus. Birds may not display symptoms of infection, and the American robin is thought to be the primary host species responsible for WNV transmission in the United States. Mosquitoes that feed on birds infected with WNV can acquire the virus, which accumulates in the insect’s salivary glands. Infected mosquitoes can then transmit the virus to other hosts as they probe the skin in search of a blood meal.

Although most people infected with WNV do not get sick, individuals over 50 years old are at the greatest risk of severe disease symptoms, and certain medical conditions greatly increase the risk of severe WNV infection. Symptoms begin appearing 2-14 days after being bitten by an infectious mosquito and include the sudden onset of high fever and headaches that can progress to stiff neck, disorientation, tremors, and coma. Permanent brain damage and death are possible in severe infections.

Prevention

There are several preventative practices for reducing mosquito populations. These include hauling away trash piles from around homes and reducing the availability of standing water. Water that accumulates in tire swings, tree holes, or other surfaces provide mosquitoes with a suitable breeding site. When possible, these structures should be filled or drilled with holes to allow draining. Practices that support natural enemies, such as avoiding the use of broad-spectrum insecticides and growing diverse plant species in landscapes, is also recommended.

Repellents

Chemical repellents

Mosquito repellents can be classified as chemical and non-chemical repellents. The chemical repellents include synthetic and natural compounds that consist of synthetic compounds, aromatic oils, and herbs. Synthetic repellents, such as DEET, are highly effective at preventing mosquito bites but may have side effects if misused. Icaridin is another synthetic repellent that is non-toxic when applied on unbroken skin. Repellent products containing picaridin as the active ingredient include other compounds with reduced toxicity toward humans. Permethrin is another example of a synthetic repellent that is applied to camping gear, bed nets, shoes, and clothing. This compound can kill mosquitoes and should not be applied to the skin as it can cause irritation.

Natural repellents consist of volatile compounds derived from plants, commonly referred to as essential oils. Due to the volatile nature of these compounds, they require frequent reapplication to be effective. Some examples of essential oils that have insect repellent properties include but are not restricted to citronella oil, lemon grass oil, rosemary, dill, eucalyptus, lavender, clove, limeone, Neem, peppermint, and cedar essential oil.

Non-chemical repellents

Non-chemical repellents are comprised of physical and mechanical methods of repelling mosquitoes. Physical methods include wearing full sleeved clothing during dawn and dusk when mosquitoes are most active, as well as screens installed in doors and windows. Mosquito nets can be medicated or non-medicated. Non-medicated nets must have mesh size small enough to physically exclude mosquitoes, and nets can be medicated by soaking in a solution containing 25% deltamethrin. Deltamethrin is recommended by the World Health Organization, but there is some evidence that suggests this compound can induce oxidative stress in nontarget species.

Mechanical repellent methods include the installation of electric mosquito zappers, which use ultraviolet light that attracts mosquitoes and an electric charge to kill mosquitoes on contact. Mosquito magnets are another device that gives off heat, moisture, and carbon dioxide, which attracts and kills mosquitoes when they come close to the device.

Chemical control

The use of aerosol sprays, foggers, and misting systems is not recommended for mosquito control due to the threat of inhalation and residual contact. Insecticides are intended to provide temporary relief from mosquitoes, and widespread use can lead to the development of resistance in the pest population.

Insecticides registered for controlling adults are known as adulticides and are applied by aircraft or via truck-mounted sprayers. Different insecticides can be used for adult control, depending on state and local agencies. Some of the most common adulticides include organophosphates or pyrethroids applied as ultra-low volume (ULV) sprays that kill mosquitoes on contact. Larvicides can also be applied as liquids, tablets, pellets, or granules to any water body where mosquitoes breed. However, these insecticides tend to have high residual activity and persist in the environment, which can have negative impacts on nontarget organisms. To ensure insecticides are being used safely, applications may benefit from the assistance of a pest control professional.

More detailed information on mosquito control is available here.

References

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EPA. 2022. Pesticides Used to Control Adult Mosquitoes. United States Environmental Protection Agency. Available https://www.epa.gov/mosquitocontrol/pesticides-used-control-adult-mosquitoes

Hazra, D., A. Samanta, R. Karmakar, K. Sen, and P. Bakshi. 2017. Mosquito vector management knowledge, attitude, practices and future of user & environment friendly new generation botanical Mosquitocide formulations: A review. International Journal of Chemical Studies. 5(3):32-37. PDF Available here

Naseem, S., M. Malik, and T. Munir. 2016. Mosquito management: A review. Journal of Entomology and Zoology Studies. 4(5):73-79. Available https://www.researchgate.net/profile/Sana-Naseem-7/publication/307965145_Mosquito_management_A_review/links/57d3ee7d08ae5f03b49144c9/Mosquito-management-A-review.pdf

Perry, O. 2014. Mosquitoes. BugwoodWiki. Available https://wiki.bugwood.org/Mosquitoes

Tenenbaum, D. 2005. A Safer Mosquito Treatment?: Minimizing Deltamethrin Risks to Children. Available https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1257625/

USU. (n.d.). Mosquitoes. Utah State University – Extension. Available https://extension.usu.edu/pests/schoolipm/structural-pest-id-guide/mosquitoes

Lu, Q et al. 2019. Deltamethrin toxicity: A review of oxidative stress and metabolism. Environmental Research. 170: 260-281.
Available https://www.sciencedirect.com/science/article/pii/S0013935118306819