Utah's Dominant Mosquito Species

Although all of the blood feeding mosquitoes in the state may at times be locally annoying only about one-third of the forty-nine species in the state are widespread or abundant enough to be a serious problem as a pest or vector of disease.

Topping the list as a pest is Ochlerotatus dorsalis which could be the most abundant mosquito in the Western United States. It has always been a major problem for mosquito abatement districts and occurs in every county of the state. Its ability to develop in highly alkaline waters as well fresh waters with multiple yearly broods makes it number one.

Aedes vexans has been designated as the most important pest species in the United States. In Utah it is a major pest species, preferring fresh water sources, although in the Salt Lake Valley it is now occurring in some marshy areas that are more typical of dorsalis.

Throughout the state in every county wherever semi permanent or permanent water sources occur two species dominate, Culex tarsalis and Culiseta inornata.

Although not as important a pest species as dorsalis, Culex tarsalis is our most important species because of its capability of transmitting the encephalitis viruses of WEE and SLE. With the arrival of West Nile in our state it could assume even greater importance.

Culiseta inornata although not a major pest species in Utah, its abundance and preference for larger mammals such as horses and cattle could make it very important if it is capable of transmitting the West Nile Virus. Encephalitis viruses have been isolated from this species, indicating at least some bird feeding.

Ochlerotatus nigromaculis is an important pest in Utah but its abundance varies from season to season and it is rarely a widespread problem.

Ochlerotatus melanimon is an important pest species in eastern Utah along the Green and Colorado Rivers' drainages and in irrigated pastures. It is rare in western Utah.

Ochlerotatus increpitus, a single brooded species, is widespread in the state, occurring in the spring in temporary pools and stream overflow. It can be a severe pest in restricted locations.

Ochlerotatus spenceri idahoensis occurs primarily in the northern parts of the state and can be a severe pest in some localities. Immense numbers of this species and Aedes vexans as well as Ochlerotatus melanimon are produced during spring overflow of the Green River in Uintah County.

Culex pipiens is a common species in many urban areas of the state. In Utah it is not a major pest species as it rarely feeds on humans. As a major bird feeder it could become very important in the transmission of West Nile Virus in birds in our state.

In the mountains of Utah four species are major pests. Ochlerotatus cataphylla, which not only is a severe biter but is common in both the higher valleys and mountainous areas. Ochlerotatus nevadensis dominates the forest pools while Ochlerotatus hexodontus is abundant in large mountain meadow marshy areas flooded by snow melt. Ochlerotatus pullatus is the most widespread occurring in a wider variety of habitats than any other mountain species.

Although there are three species of Anopheles in Utah only one, freeborni, is common throughout the state. Females often become annoying pests as they emerge from their over-wintering sites in the spring. One tree-hole species, Ochlerotatus sierrensis, is a major problem in Salt Lake, Davis and Weber counties. Not only a source of many complaints during spring and summer in residential areas, it is also responsible for a rising number of dog heartworm cases along the Wasatch Front.

Another Culex species which can be a problem in favorable years is erythrothorax. Larvae overwinter during mild winters and adults can be very annoying to duck hunters and people living close to marshy areas where it occurs.

Lewis T. Nielsen