October, '21] freeborn: anopheles occidentalis 415 



THE SEASONAL HISTORY OF ANOPHELES OCCIDENTALIS 

 D. & K. IN CALIFORNIA! 



By Stanley B.Freeborn, Unwersity of California 



The control of malarial mosquitoes has been operated for years on the 

 assumption that Reaimiur's classical work on the life history of Culex 

 pipiens was a suitable basis for the life history of all mosquitoes. It is 

 only within a comparatively few years that ecological studies have been 

 conducted with anopheline mosquitoes to lay the foundation for a more 

 economical and efficient method of control operation than that which 

 followed the old slogan of "Oil or drain all standing water" with no ref- 

 erence to type of breeding place, presence of larvae, or time of year. 

 There is no question in the writer's mind regarding the success of a 

 campaign carried out along these lines, but in the light of what we know 

 regarding selective breeding and the limited generations of the insects, 

 the waste in materials, time, and energy of these "shotgun" methods is 

 appalling. 



Perhaps the most important field for improvement can be based on the 

 study of the life histor^^ It was the writer's good fortune to be detailed 

 to co-operate in June 1919 with a party of U. S. Public Health Service 

 officers at Chico, California where investigations were being carried on 

 regarding the status of anopheline mosquitoes in the rice fields. In this 

 month he began a weekly collection of all mosquitoes appearing under a 

 highway bridge situated some distance from the nearest rice field. This 

 procedure was maintained by the writer until other work called him 

 away in August after which Mr. W. C. Purdy, special expert of the U. S. 

 P. H. S., made the weekly collections forwarding them to the writer for 

 identification. The bridge under which the collections were made was a 

 modern, concrete, highway structure spanning a natural drainage slough, 

 continually holding water but without a noticeable current in the im- 

 mediate vicinity of the bridge during most of the year. Mosquito 

 breeding, during the season, was prolific in many parts of the slough. 

 No control measures were undertaken within five miles of the bridge. 

 Collections were made in shell vials containing chloroform or cyanide, 

 the specimens transferred to pill boxes and transported to the laboratory 

 for identification. All mosquitoes resting on the roof or sides of the 

 bridge were taken except on certain occasions when the single collection 

 would have run into the thousands. At such times the distribution of 

 the mosquitoes under the bridge was observed and enough sections 



^Contribution from the Division of Entomology and Parasitology, Univ. of California, 

 College of Agriculture. _ ^ 



