412 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 14 



While the two groups of Sierra counties, northern and middle, show an 

 approximately equal m,alaria death rate, nam.ely 9.1 for the form.er and 

 10.5 for the latter, there is much divergence in the anopheline m.osquito 

 population, as far as collections were m.ade. Owing to a tim.e limit in 

 canying on the sur\"ey during 1919, the middle Sierra counties were not 

 as well covered as had been contem.plated, and in the second place Mari- 

 posa County, herein included, represents a strong transition, both in 

 faunal and topographic -conditions, factors which are not easity overcome 

 in a classification based on county lines. In spite of this there is, never- 

 theless a high percentage of Anopheles punctipennis. 



The coastal counties, northern, middle and southern, show a much more 

 consistent rate, both for m.alaria and for Anophelines, i.e. a very low 

 m.alaria rate and a veiy high rate of A . psetidopimciipemiis , the predomi- 

 nant Anopheline. 



That the relation between potentially efi'ective anopheline carriers 

 alone and the m.alaria rate should not be pressed too hard is indicated by 

 the fact that the com.bined A. occidentalis and A. punctipennis rate for 

 the San Joaquin Valley stands at IS. 8 per cent, with a malaria death 

 rate of 6.3 per 100,000 population, as compared with Southern Cali- 

 fornia with a rate of 15.2 per cent (^4. occidentalis and A. ptmctipennis 

 and a m.alaria death rate of only .9 per 100,000. In other words, if the 

 potentially efi'ective Anopheline rate alone were a sufficient indicator of 

 malaria incidence. Southern California should have a much higher rate 

 than it actually has. This seeming discrepancy is readily explained by 

 the fact that the two areas in question are in reality not comparable, 

 owing to divergent fundam.ental physical factors which control biological 

 phenomena. For exam.ple, one often travels many m.iles and tries many 

 times in the more arid part of Southern California before mosquitoes of 

 any kind are encountered, and then they may be present in considerable 

 numbers, i.e. they occur in isolated and widely separated spots. Thus, 

 for example, after m.any miles of travel and careful search without success 

 rather suddenly our party encountered enormous numbers of Anophe- 

 les occidentalis at a hot springs resort in Riverside County, in a district 

 rem.oved from, centers of population. Again, many of the Anophelines 

 (.4. occidentalis) in this part of the state were taken in Ventura County, 

 particularly near the city of Ventura, where the sumjner temperature is 

 uniformly quite low, vitally influencing biological interrelationships. 

 The occurrence of malaria is dependent upon a combination of factors in 

 addition to the presence of potentially efi'ective mosquito carriers, among 

 them, being temperature (both above and below a certain range), prox- 

 imity of population to anopheline foci, a sufficient production of Ano- 

 phelines, etc. 



