Introduction: Mosquitoes are well known by most people because of their annoying biting habit. Of greater concern, they are very important as vectors of numerous human diseases such as malaria, yellow fever, filariasis, dengue, encephalitis, and West Nile virus. Only female mosquitoes are known to bite (take blood meals on) humans and other host animals. The short-lived males feed exclusively on nectar from blossoms. Recognition: Adult mosquitoes are about 1/4 to 3/8 inch long. Mosquito color patterns are due to the wings, body and legs being covered with scales. Color combinations include brown, gray, black, white and silver. Similar Insects: (1) Midges (Chironomidae) are attracted in great numbers to lights at night, around ponds and lakes in which they breed. These midges do not bite. (2) Crane flies (Tipulidae) have slender bodies and long legs. Crane flies do not bite but are often mistaken for giant mosquitoes. They are attracted to light as well.
Colorado Representative Species
Culex Pipiens – the Northern House Mosquito
Body: Brown, medium sized mosquito
Legs: Brown and unbanded
Season: Year round- peaking during summer and fall
Larval Habitat: In warm, sheltered foul or polluted water, such as fish ponds, catch basins, waste treatment ponds, and neglected swimming pools.
Biting Behavior: Feeds on birds and mammals. Readily enters homes and bites indoors at night.
Importance: Can transmit WNV, Western Equine Encephalitis, and St. Louis Encephalitis.
Culex Tarsalis – The Western Encephalitis Mosquito
Body: Medium-size, brown with a white band on the proboscis, or biting part, and V’s on the abdomen.
Legs: Black and white banded.
Season: Primarily Spring to Fall.
Larval Habitat: Wide range of habitats from clean to partially foul water; rain pools, irrigation water, ornamental ponds, and often agriculture.
Biting Behavior: Prefer birds, but often feed on humans at night.
Importance: Primary vector of West Nile virus, Western Equine Encephalitis, and St. Louis Encephalitis.
Aedes Dorsalis – The Summer Salt Marsh Mosquito
Body: Whitish to yellow
Season: Adults are active late spring into the fall
Larval Habitat: Tidal or reclaimed marshes, or inland irrigated pastures
Biting Behavior: Vicious all-day biters, they can fly far for a blood meal, return to the marsh to lay eggs
Importance: Major pest and secondary vector for Western Equine Encephalitis
Body: Black and brown with white and grey markings – most easily recognized by the sideways “B” shaped markings on each abdominal tergite
Legs: Brown and banded
Season: Lavae – April – September, Adults – May – October
Larval Habitat: Flood water mosquito. Eggs are laid offshore when heavy rains come and the flood waters rise, rain floods the eggs and they then hatch
Biting Behavior: Tend to bite during two narrow time periods of the day – immediately after dark and then again immediately before dawn. Females prefer only the blood of mammals for protein meals.
Importance: One of the most serious pest mosquito due to its abundance, widespread distribution and breeding potential in floodwater habitats
Biology of Mosquitoes
Mosquitoes are commonly separated into 3 groups based on where and how their eggs are laid. After a blood meal, the female will lay:
1) eggs with floats singly on water; they usually hatch within a few days (e.g. Anopheles species);
2) eggs in rafts on water with up to 100+ eggs per raft; they usually hatch within a few days, (e.g. Culex species); and
3) eggs singly in semi-dry places such as moist soil near water; they do not hatch until water has risen and inundated them; these eggs can lie dormant for 3 to 5 years (e.g. Aedes, Ochlerotatus and Psorophora species).
With water present, eggs hatch in a few days into larvae which are commonly called wigglers because of their jerky movements. All larvae live in water and go through 4 growth stages. Larvae of most species (e.g. Aedes and Culex) take in air through a breathing tube (siphon) located at the rear which penetrates the water surface while they float at an angle just below the surface. Other species (e.g. Anopheles) have a spiracular plate on the last abdominal segment which penetrates the surface while they float parallel to and just below the surface, their buoyancy enhanced by clusters of float hairs (palmate hairs) on some abdominal segments.
With their 4th molt, the larvae become pupae which are commonly called tumblers. The pupae live in water and are very active. The pupae of most species breathe through a pair of respiratory trumpets located on the dorsal thoracic surface which penetrate the water surface while they float just below the surface. At the end of the pupal stage, while at the water’s surface, the pupal skin splits open and the adult works its way out and onto the surface of the water, dries briefly and flies away. Development time (egg to adult) is usually about 10 to 14 days: Eggs hatch in 1 to 3 days, although some remain viable for up to 5 years. The larval stage lasts one to several weeks and the pupal stage takes from 2 days to a few weeks. Adult females may live 1 to 2 months while males live about 6 to 7 days in the summer, or up to 6 months if they overwinter.
Mosquitoes serve as vectors of many important diseases affecting humans including malaria, yellow fever, dengue fever, filariasis, encephalitis, and West Nile Virus. Some mosquitoes also transmit dog heartworm.
Habits: Mosquitoes have adapted to almost every kind of aquatic situation such as permanent ponds and marshes, temporary flood waters or woodland pools, drainage ditches, and water contained in tree holes, leaves of plants, or artificial containers. The exceptions are flowing streams and the open waters of large streams, rivers lakes, seas, and oceans. The number of generations per year ranges from 1 where the eggs require cold before hatching (e.g. some Anopheles), to dozens in warm climates where most breed continuously.
The larvae of most species feed on small aquatic organisms and organic debris which they strain out of the water. Although quite active, the pupae do not feed. The adult males feed on nectar. Although the adult female also feeds on nectar, females of most species require a blood meal before they can lay fertile eggs. Females require 2+ days to digest a blood meal, lay a batch of eggs, and then seek another blood meal.
The flight range of mosquitoes varies with the species, temperature, wind direction, time of year, and distance to blood meal sources. Normal flight ranges of mosquitoes are in the range of 1/2 mile to 10 miles, depending on species.
The time of day in which biting occurs varies with the species. Most medically important species bite at dusk and dawn (crepuscular) and also during the night (nocturnal) such as the vexans mosquito and the northern house mosquito; whereas, others bite only at dusk and dawn such as the eastern saltmarsh mosquito (Ochlerotatus sollicitans). Several species of medical importance bite only during the daytime (diurnal) such as the Asian tiger mosquito. Some species which normally do not bite during daytime will do so if disturbed, such as the floodwater mosquito.
Cultural Control & Preventative Measures: At the household level, relief can be achieved by preventing entry to structures via proper screening and sealing. On the personal level, the use of repellents is quite effective. Weekly emptying, or eliminating completely, containers which hold water on one’s own property can be of great help in reducing the number of local mosquitoes. This is especially true for mosquitoes that live in close association with humans and have short flight ranges. Discarded tires, old paint cans, unattended bird baths and children’s splash pools, upright wheel barrows, unpatched tree holes, clogged gutters, stagnant drainage ditches and low spots that hold rain water for days at a time are all susceptible and correctible mosquito breeding sites.
Professional Control: Mosquito control begins with an accurate and thorough assessment of the problem through surveys and then choosing the control measures best suited to the situation. Integrated mosquito management involves a combination of techniques: (1) to eliminate mosquito breeding sites via habitat modification (source reduction); (2) to control mosquito larvae by introducing insect growth regulators (IGR’s), microbial larvicides (e.g. pathogenic bacteria) and predatory fish; and (3) to control adults via pesticide fog applications and applying appropriately labeled residual insecticides to resting surfaces.