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<br />Large numbers of biting mosquitoes also cause serious economic <br />losses by reducing the efficiency of industrial workers, lessening <br />the value of real estate, restricting outdoor recreational activities, <br />and reducing attendance at outdoor business establishments such as <br />drive-in theatres and eating places. <br /> <br />The economic magnitude of the irrigation~osquito problem alone <br />18 illustrated by expenditures for abatement of these insects. For <br />example, in California over $5,000,000 is spent annually to control <br />encephalitis and other irrigation mosquitoes and it has been estimated <br />that at least twice this amount would be required to provide adequate <br />control throughout the State. Approximately $200,000 is spent each <br />year for mosquito abatement in a few irrigated areas in Utah. Many <br />urban communities in other western irrigated areas spend large sums of <br />money each season for chemical control to provide partial protection <br />from mosquitoes. Individual families also spend sizable amounts of <br />money each summer for household sprays, mosquito repellents, live- <br />stock sprays, .and medicine for treatment of mosquito bites. The total <br />cost of controlling irrigation mosquitoes, together with the other <br />serious economic losses they cause, runs into many millions of dollars <br />each year. Thus, mosquitoes are a major economic liability in many <br />irrigated areas. <br /> <br />Other Aquatic Insects <br /> <br />Several other groups of aquatic insects may be produced in <br />sufficient numbers in habitats associated with water resource project. <br />to create public health and economic problems. Deer flies and horse <br />flies (Tabanidae) are produced along the margins of impoundments and <br />in seeps and marshes in irri&ated areas. These insects are vicious <br />biters of both man and livestock and are somctl.mes involved in the <br />transmission of diseases such as tularemia and anthrax. Some species <br />of small gnats of the family Heleidae are also vicious biters and <br />often produce severe reactions and vesicular lesions. These gnats <br />are produced in damp areas of many irrigated valleys as well as salt <br />marshes and other wetland areas. In certain areas, black flies <br />(Simuliidae) plague both man and livestock with their irritating and <br />painful bites. They are normally produced in streams but sometimes <br />occur in large numbers in irrigation conveyance systems. The small <br />nonbiting midges (Tendipedidae) and the phantOlll midges (Chaobor1nae) <br />are another group of pestiferous insects which may be produced in <br />impounded water. These insects are attracted to lights in tremendous <br />numbers and cause severe human annoyance. An example is the Clear <br />Lake gnat, Chaoborus asticopus, which creates serious problems at <br />the ,resort areas 'in Lake County, California. <br /> <br />B-3 <br />