142 



methods should be de%nsed in order to check the rapid increase which 

 follows any failure of the present system during a period of trying 

 weather. 



Freeborn (S. B.). The Rice Fields as a Factor in the Control of 

 Malaria. — Jl. Econ. Entom., Concord, N.H., x, no. 3, June 1917, 

 pp. 354-359. 



In a previous paper the author has drawn attention to the influence 

 which the introduction of rice culture into California may have upon 

 the increase and control of malaria [see this Review, Sex. B, v, p. 40]. 

 ^Vhile, theoretically, the conditions of rice-growTing should be ideal for 

 the breeding of mosquitos, it must be borne in mind that the majority of 

 species of Anopheles are limited to very definite areas. For example, 

 A. Tnahf actor, a tropical species, breeds almost exclusively in hollow 

 tree-trunlvs, while A. ludlowi is limited to brackish or tidal waters. 

 It has been sho-^Ti that the rice areas of the Philippines are remarkably 

 free from malaria, because the typical rice-field mosquito, A. rossi, 

 is only a slight carrier of malaria, while A. yninimus {febrifer), which is 

 the intensive carrier, is a stream-breeder whose breeding-places are 

 destroyed with the introduction of rice cultivation. It is therefore 

 considered possible that the development of rice culture in the Philip- 

 pines may result in the diminution of malaria. In the Federated 

 Malay States rice culture has actually been suggested as an anti- 

 malarial measure. Each district, then, requires separate investigation, 

 and in order to determine the importance of the rice-field mosquitos 

 as a factor in the control of malaria, it is necessary to ascertain what 

 species of Anophelines breed in and around the rice-fields, their 

 susceptibility as malaria-carriers and their relative abundance. 



In the Californian rice-fields the two most prevalent species are 

 A. occidentalis, D. & K., and A. pseudopunctipennis, Theo. While 

 A . occidentalis has never been tested experimentally with regard to its 

 susceptibility as a malaria-carrier, it is one of only two Anophelines 

 that are found in highly malarial districts, and the other, A. pseudo- 

 putictipennis, is known to be only slightly susceptible. Its close 

 connection and possible identity ^dth A. quadrimacidatus, a known 

 malaria-carrier in many parts of the United States, also indicates the 

 probability of A. occidentalis being the chief carrier. A. quadri- 

 maculatvs has been stated to be a carrier of tertian and quartan types 

 of malaria and also of aestivo-autumnal fever. It seems highly 

 probable then that A. occidentalis is the important carrier in California, 

 while a few infections may be due to A. pseudopnnctipennis. 



It is known that a heavy and uniform growth of rice produces 

 relatively few mosquitos, while a sparse stand with irregular growth 

 generally breeds Anophelines in large numbers. Far more dangerous 

 than the fields, however, are the overflow pools of surplus water ; and 

 these are entirely unnecessary. The control of breeding places outside 

 the rice fields before, after and during the rice season, combined with 

 sound methods of rice cultivation, would do much towards the control of 

 mosquitos. Unfortunately, a large percentage of the rice is cultivated 

 by tenant farmers whose only object is to reap speedy and lucrative 

 returns, with the result that irrigation is badly organised and the 

 agricultural methods are poor, while the labourers, whose shelters are 



