Bionomics of Culex Tarsalis in Relation to Western Equine Encephalomyelitis

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The North American distribution of the mosquito Culex tarsalis Coq. is presented in detail and it compares well with the range of the severe 1941 epizootic of the Western equine encephalomyelitis virus in horses. This mosquito has been found to be naturally infected with this virus in six widely distributed areas over its range which extends throughout the great plains, prairies, and western irrigated areas.

During the war period 1942–1946 the known distribution of C. tarsalis was extended 500 miles eastward to South Carolina. The species may have been discovered in this area due to more intensive collecting during that time, or the species may have been introduced due to increased airplane and vehicular traffic in that area. The mosquito is most abundant in the western states and becomes less common eastward. The peak of adult abundance in the western United States is in July and August, and eastward the population maximum occurs progressively later until in the southeast, adults are found only in late fall and winter.

The main hosts are wild and domestic animals which are attacked at dusk and night. Human beings are not important hosts. The larvae breed in a large variety of habitats and under a wide range of conditions

Author Notes

Medical Division, Army Chemical Center, Maryland. This paper is based upon work sponsored in part by the Biological Department, Chemical Corps, Camp Detrick, Frederick, Maryland.