The Northern house mosquito, Culex pipiens, is a common mosquito across urban, suburban, and rural habitats in Ohio. This species is ubiquitous across the northern temperate zone, including North America, Europe, and Asia, and has been reported in every county across Ohio. These mosquitoes and their close relatives spread many deadly and life-altering diseases, making them a dangerous pest in Ohio. Among these diseases, the most concerning are Eastern equine encephalitis, St. Louis encephalitis, and West Nile virus (WNV).
Mosquitoes are a type of fly with fragile, slender bodies and six long legs. They have one pair of wings covered in scales and a noticeable tube-like mouthpart called a proboscis. The size of the Northern house mosquito varies from 3 to 7 millimeters. These mosquitoes are often dark brown to tan in coloration and are easily identified by brown and white stripes alternating on the top of their lowest body segment, the abdomen (Figure 1). Males are morphologically similar to females but are slightly smaller and have antennae that are feather-like (Figure 2). There are several common mosquitoes in Ohio that look like the Northern house mosquito, such as Culex restuans, Culex salinarius, and Culiseta impatiens. These other species, while they may bite humans, are considered to be less important or not important in transmitting diseases to humans. If you collect a mosquito and would like it to be identified to species, contact the C. Wayne Ellett Plant and Pest Diagnostic Clinic at ppdc.osu.edu for identification and management recommendations.
Life Cycle and Habits
The adult female mosquito, like the male, feeds on nectar for daily energy needs. However, the female requires proteins and iron from blood to produce eggs. Female mosquitoes use specialized mouthparts to pierce into host capillaries and suck blood while simultaneously releasing anticoagulants in their saliva to maintain blood flow (Figure 3). These anticoagulants and other proteins in the mosquito saliva can cause a mild to severe allergic reaction in the skin of human and animal hosts, leaving a red and itchy welt near the mosquito bite. Female mosquitoes find their hosts primarily by detecting heat and carbon dioxide, but other olfactory cues and signals may be involved, including lactic acid and 1-octen-3-ol, which are components of sweat (McMeniman et al. 2014).
Females of the Northern house mosquito lay eggs in clusters called rafts on pools of calm water. They prefer natural habitats such as stagnant water in ditches, large puddles, and ponds, and artificial habitats such as catch basins, bird baths, flowerpots, and rain gutters filled with water. This preference classifies them as “container-breeding mosquitoes.” They also tend to prefer water that is murkier and has more bacteria than most other mosquitoes.
The Northern house mosquito has four life stages: egg, larva, pupa, and adult. Only adult females consume blood and transmit disease.
Typically, female mosquitoes lay their eggs three to five days after obtaining the blood meal, although this depends on temperature and humidity. Females deposit eggs on the surface of water-holding containers in a raft consisting of around 150 eggs glued together (Vinogradova 2000). Initially the rafts are white (Figure 4), but they quickly harden and become dark black in color (Figure 5). The egg rafts float on the surface of the water and can vary slightly in shape but are generally elongate oval or tear-drop shaped with the surface being slightly concave.
Larvae emerge from the eggs into the water one to three days after being laid (Figure 6). The larvae are prone to predation, disease, or desiccation. Because larvae lack gills, siphon tubes are used to breathe air. Thus, larvae are often found near the surface of the water. They quickly move away, however, if the water is disturbed or a shadow is cast over them. They exhibit a wriggling motion to swim and eat, so they are often termed “wrigglers.” Mosquito larvae are easy to mistake for tadpoles or many other aquatic organisms, but they can easily be distinguished by the large, cream-colored thorax before their head segment and the thin, long siphon. The duration of the larval stage is highly variable and ranges anywhere from five to14 days depending on temperature, competition with other mosquito larvae, and available nutrients (Vinogradova 2000). Larvae shed their exoskeleton four times before becoming pupae.
Pupae are small, dark brown, and comma-shaped (Figures 8 and 9). The pupae also breathe air through structures called trumpets located on their thorax and tumble when disturbed. Therefore, they are sometimes referred to as “tumblers.” Pupae do not feed. Northern house mosquitoes remain in the pupal stage for approximately two days before emerging as adults. To determine if mosquitoes have emerged from a body of water, look along the sides of a container of water for empty husks or exuvia of the pupae (Figure 10).
Both male and female adult mosquitoes consume nectar. Nectar provides energy for flight and mating. Female Northern house mosquitoes generally mate once (Bullini et al. 1976), whereas males can mate several times (Huck et al. 2021). After mating, females search for vertebrate hosts so they can acquire the blood that provides proteins and other nutrients necessary to develop eggs. Birds are preferred hosts, but humans and dogs are commonly accepted. Eggs are laid three to five days after a blood meal, and females take another bloodmeal soon after. This is important to disease transmission because female mosquitoes are usually able to spread a pathogen, such as West Nile virus, only after first biting an infected bird. The adult lifespan varies depending on humidity, temperature, and predation, but they can live several days to one month over the spring and summer. Some females of this species survive Ohio winters by entering a hibernation-like state called “diapause.” In Ohio, female mosquitoes enter this state in response to the shorter days of August through October. At this time, they are not interested in taking a blood meal but do gorge on plant nectar so they can acquire the fat necessary to survive the winter (Figure 11) (Robich and Denlinger 2005). Female mosquitoes emerge from their overwintering state in response to higher temperatures in March and April when they resume feeding on nectar and biting vertebrate hosts.
The Northern house mosquito is more active during the twilight hours. Females typically bite humans and animals in the evening, and male and female mosquitoes prefer to rest in shady habitats during the day (Vinogradova 2000). Although purported to be most abundant in urban settings, Northern house mosquitoes can also be found in suburban and even rural areas (Honnen et al. 2017). Northern house mosquitoes tend to not travel far distances, travelling at most three-fourths of a mile from their larval breeding sites. Their presence indicates that larval habitat is nearby.
Importance as a Disease Vector
Because these mosquitoes transmit several diseases to humans and other animals, county and local public health offices routinely collect mosquitoes and test them for the presence of West Nile virus (WNV) from May to September. This is because WNV is the most common mosquito-borne pathogen in Ohio. Therefore, public health officials are committed to closely monitoring mosquito abundance and virus prevalence every summer when people, birds, and horses face the greatest risk of infection. When a local health agency detects WNV in collected mosquitoes or when a human case is confirmed, it quickly deploys control efforts in the region, generally by fogging and treating with pesticides to kill adult mosquitoes and applying larvicides to potential breeding habitats to kill immature mosquitoes. The turnaround from surveillance to treatment takes about two to three weeks, which effectively limits the spread of WNV. This has reduced the human case load to an average 58 confirmed cases and four deaths a year of Ohioans, including cases acquired from other locations (Ohio Department of Health 2021).
Northern house mosquitoes are ornithophilic, meaning they generally prefer to bite birds especially throughout the spring and early summer (Farajollahi et al. 2011). Some studies suggest that in late summer and early fall, female Northern house mosquitoes are more inclined to bite humans and mammals (Kilpatrick et al. 2006). Therefore, humans face the greatest risk of being bitten by an infected female mosquito and contracting West Nile fever starting in June until the middle of October. Most people who are infected with WNV experience mild, cold-like symptoms, including a fever and chills that typically last for a few days. These mild symptoms have most likely resulted in the number of human cases of WNV infection being underreported (Colpitts et al. 2012). However, some people with WNV experience severe symptoms, including high fever, headache, stupor/disorientation, tremors, muscle weakness or convulsions, vison loss, numbness, paralysis, coma, and even death. People suffering from hypertension, diabetes, and heart diseases often experience more severe WNV symptoms. Age and sex also seem to increase risk, with men over 50 appearing to be at higher risk for severe disease. If you are at risk, be sure to take the precautions of limiting skin exposure and wearing mosquito repellants when outside during dawn and dusk throughout June to mid-October. For more information, please see the Ohio Department of Health’s West Nile virus page, information from the Centers of Disease Control, and The Ohio State University fact sheet “How to Control and Prevent Mosquito Bites In and Around Ohio Homes.”
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