June, '17] FREEBORN: RICE FIELDS AND MALARIA 355 



Barber has shown that the rice areas of the Philippines are singularly 

 free from malaria clue to the fact that the typical rice field anopheline, 

 A. rossi, is only a weak and somewhat doubtful carrier of malaria 

 while the intensive carrier, A. fehrifer, is a stream breeder whose breed- 

 ing places are destroyed with the introduction of rice paddies. He fol- 

 lows these remarks with the statement that " ... in some parts 

 of the Philippines the further development of rice culture may result 

 in the diminution of malaria." 



Watson, writing of malaria con(,litions in the Federated Malay 

 States, comments on the absence of malaria in the rice districts and 

 its abundance in the hill country and suggests rice culture as an anti- 

 malarial measure. 



Kendrick, working in central India, observed that the rice districts 

 on the broad open plains were practically free from malaria but that 

 when shade such as that afforded at the edge of the jungles was present 

 the species of anopheles changed and malaria was present. In all of 

 these instances of malaria free rice districts, the anophelines present 

 lacked the ability to transmit malaria or were relatively weak carriers. 



From these findings of men who have dealt with the problem in 

 various countries and under different conditions, the only safe de- 

 duction that can be made is the fact that each district requires separate 

 investigation regardless of apparent similarity. The Californian 

 problem can not be settled by Indian or Philippine investigations or 

 even by those under way in our own southern states. 



In order to determine, therefore, the relative importance of the rice 

 field mosquitoes as a factor in malaria control, it is necessary to ascer- 

 tain (1) what anophelines breed in the rice fields and the pools adjacent 

 to and caused by them, (2) their susceptibility as malaria carriers, 

 and (3) their relative abundance. 



In the Sacramento Valley rice fields two anophelines find reasonably 

 satisfactory breeding grounds judging from the number of larviB taken. 

 Anopheles occidentalis D. & K. and A7iopheles pseudopunctipennis 

 Theob. are both present in large numbers, making up about one half 

 the mosquito population of the district. Probably 70 to 80 per cent 

 of these two species find their breeding places in the pools attendant to 

 the rice fields and caused by seepage, overflow and faulty water regula- 

 tion. The other 20 to 30 per cent breed in the rice fields proper in the 

 shallow water near the contour checks. 



A. occidentalis is a recently named species which was previously 

 considered to be ^. quadrimaculatus, the principal eastern and south- 

 ern malaria-carrier. Nearly a thousand specimens of A. occidentalis 

 in our collection show all stages of resemblance to A. quadrimaculatus 

 from those fairly well defined to those that are practically identical 



