354 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 10 



THE RICE FIELDS AS A FACTOR IN THE CONTROL OF 



MALARIA 



By Stanley B. Freeborn, Instructor in Entomology, University of California 



The introduction of rice culture into the Sacramento and San 

 Joaquin Valleys of California has called forth much comment as to its 

 possible influence upon the increase and control of malaria which is 

 already endemic in both valleys. Rice was first grown commercially 

 in California in 1912 when 1,400 acres were planted at Biggs in the 

 Sacramento Valley. The acreage has increased at the rate of over 

 100 per cent a year since that time until 1916 saw about 75,000 acres 

 under cultivation. The industry is an exceedingly fortunate one owing 

 to the fact that land rendered useless by previous cropping or unfit for 

 other crops on account of faulty texture has been used for rice, thus 

 adding materially to the state in wealth. 



The cultivation of rice demands that the entire acreage be flooded 

 to the depth of four or five inches with water stagnant or in a gentle 

 current for a period varying from 145 to 160 days beginning about 

 June first. 



Theoretically, at least, these large bodies of standing water, well 

 areated by a gradual addition of water and the presence of the growing 

 rice, should form ideal breeding places for malaria-bearing mosquitoes. 

 However, there is a deep grounded belief among those who deny the 

 ability of the rice fields to produce mosquitoes, that there is an "es- 

 sential something" in the rice fields that prevents mosquito breeding. 

 This "essential something" is explained by another mystery, — the 

 ecological factors governing the habitat of the different species of 

 mosquitoes. Just as salmon, brook-trout, and steel-heads choose 

 different breeding grounds, so the different species of anophelines in- 

 variably deposit their eggs in locations where a given set of determin- 

 ing factors are present. Some, it is true, have a wide range of selection 

 but the majority are limited to very definite locations. For example, 

 A. malefactor, a tropical anopheline, breeds almost exclusively in hol- 

 low tree trunks while A. ludlowii is limited to brackish or salt tide 

 water. Again A. fehrifer, a Philippine malaria carrier finds its ideal 

 habitat at the edge of running streams and is seldom present in stag- 

 nant pools as is the case with our domestic anophelines. The state- 

 ment that California rice fields will not furnish breeding grounds for 

 malaria-bearing mosquitoes is based solely on the empirical application 

 of the knowledge that in certain parts of the world, the hypersusceptible 

 anophelines of the district do not find their natural breeding places in 

 the rice fields. 



