22 



Usinger: Introduction 



breeding places (drainage, filling), for altering the 

 habitats of larvae (flooding, stranding), and for con- 

 trolling larvae by the introduction of top minnows 

 (Gambusia). Then, during World War II, DDT started 

 a revolution in chemical control somewhat comparable 

 to the effect of antibiotics on the practice of medicine. 

 At the present time mosquito control, in spite of 

 complications due to the development of resistance 

 to the newer insecticides, is a highly effective opera- 

 tion. It calls for sound knowledge of the systematics 

 and biology of mosquitoes and the best of modern 

 engineering practices. Furthermore, as a result of 

 public information gained during World War II, and other 

 reasons, mosquito control is more widely demanded 

 and supported than ever before. 



In California, certain aspects of mosquito control 

 have been simplified whereas others, owing to climatic 

 and other circumstances, have been accentuated. 

 The dengue-yellow fever vector, Aedes aegypti, does 

 not occur here, thus obviating the necessity for routine 

 house-to-house inspection of artificial containers such 

 as tin cans, bottles, flower vases, and so on. Of 

 mosquito-borne diseases, the tropical filariasis is 

 absent. Malaria, on the other hand, was a major 

 problem in times past and remains as a potential 

 threat in periods of mass movement of possible 

 carriers, since the mosquito vector, Anopheles free- 

 borni, is as abundant as ever. Historically, California 

 played a pioneering role in malaria control (Herms, 

 1913). "Thirteen Central Valley counties, with an 

 area of about 20,000 square miles, and harboring three- 

 fifths of all the malaria, had a death rate of 14.2 per 

 100,000 as late as 1916. These counties comprised 

 an area about half the size of Mississippi, which had 

 a reported death rate of 5.9 per 100,000 — and Missis- 

 sippi was regarded as one of the most malarial states 

 in the country". (Mosquito Abatement in California, 

 1951). Sporadic cases occurred when carriers entered 

 the area during the depression years and when a 

 carrier returned from Korea in 1953 and started a small 

 epidemic, with thirty-two proven cases (Brunetti, et al.). 



The reasons for the disappearance of endemic 

 malaria are not fully understood in California or 

 elsewhere, but it is thought that widespread control 

 by the public and higher standards of living have 

 contributed to the present freedom from the disease. 



Another mosquito-borne disease is encephalitis or 

 sleeping sickness. In California, three strains of 

 virus are known: the Western equine, St. Louis, and 

 California strains. Culex tarsalis is the only impor- 

 tant vector, according to present knowledge, but 

 thirteen other species have been found harboring the 

 viruses in nature or capable of transmitting them in 

 the laboratory. Information is still not complete 

 (Reeves, 1953) but a diagram of the probable infection 

 chain in Western equine encephalitis is given below 

 (intro. fig. 26), based on studies conducted under 

 the direction of the Hooper Foundation for Medical 

 Research. Great effort is now being made to control 

 the mosquito-borne encephalitides but, unlike malaria, 

 the problem has not yet been solved and cases occur 

 every year, some of which result in damage to brain 

 tissues, paralysis, or death. 



MITE 



MITE 



BIRD 



(Sparrow-Finch) 



A 



MOSQUITO 

 ft larsalii) 



■ I 



(L. sylviorutr) (L. sylviarum) 



MAN 



(Sparrow-Finch) 



MOSQUITO 



(A. dorsal,,) 



Intro, fig. 26. Infection chain for western equine encephalitis 

 (Mosquito Abatement in California, 1951). 



Pest mosquitoes. — Long ignored in many parts of 

 the world, pest mosquitoes have received attention 

 mainly near large centers of population (New Jersey, 

 Florida, the Chicago area, the San Francisco Bay 

 area, and elsewhere). In California the most important 

 pest mosquitoes are -salt-marsh species (Aedes dor- 

 salis, Aedes squamiger, and Aedes taeniorhynchus); 

 domestic mosquitoes (Culex pipiens, Culex quinque- 

 fasciatus); mosquitoes of irrigated areas (Aedes 

 nigromaculis, Aedes dorsalis, Culex tarsalis); tree- 

 hole mosquitoes in the deciduous forests of coast 

 range and foothills (Aedes varipalpus); and snow 

 mosquitoes (Aedes communis, Aedes hexodontus). 



The control of pest mosquitoes has lagged in some 

 places because funds are usually earmarked for 

 disease vectors. California is an exception to this, 

 with an efficient and extensive organization for pest- 

 mosquito abatement. This is contributing in no small 

 measure to the high land values, increased enjoyment 

 of recreational areas, and increased efficiency of 

 workers out-of-doors. 



Mosquito control. — In 1915 the Mosquito Abatement 

 District Act was passed by the state legislature. In 

 subsequent years this resulted in forty-three local 

 areas (intro. fig. 27) (counties or other areas) organ- 

 izing for mosquito control and supporting the work 

 with tax rates up to 40 cents on each $100 of 

 assessed valuation. Also nine local health depart- 

 ments are active in mosquito control. Mosquito Abate- 

 ment Districts are governed by boards of trustees 

 which establish policies and employ a manager to 

 carry out the program of the district. "The District 

 has the power to enter upon and inspect lands for 

 mosquito sources, and to take appropriate measures 

 to abate mosquitoes thereon, whether such lands be 

 within or outside of the district; to acquire land or 

 rights of way for drains or other purposes; to purchase 

 supplies and equipment for the work, etc." The 

 technical staff of a district includes a manager and 

 usually one or more entomologists, inspectors, fore- 

 men, and so on. Technical guidance and support is 

 provided to the districts by the Bureau of Vector 

 Control of the State Department of Public Health. 

 The Bureau of Vector Control also conducts investi- 

 gations of particular problems that are beyond the 

 scope or facilities of the individual districts. 



Role of the entomologist in mosquito control pro- 

 grams. — Very early in the development of mosquito 

 control programs it was realized that "shot-gun" 

 methods were expensive and not very effective. 



