606 PROTOZOOLOGY 



at room temperature (18-22°C), development takes place in a short 

 while and motile microgametes are produced ("exflagellation"). 

 Similar changes take place when the gametocytes are taken into 

 the stomach of mosquitoes belonging to genera other than Anopheles, 

 but no sexual fusion between gametes occurs in them and all degener- 

 ate sooner or later. In the stomach of an anopheline mosquito, how- 

 ever, the sexual reproduction of human Plasmodium continues, as 

 has been stated before. 



All species are transmitted by adult female mosquitoes. The males 

 are not concerned, since they do not take blood meal. The species of 

 Plasmodium which attack man are transmitted only by the mosqui- 

 toes placed in genus Anopheles, while the majority of the avian spe- 

 cies of Plasmodium are transmitted by those which belong to genera 

 Culex, Aedes, and Theobaldia. The chief vectors of the human ma- 

 larial parasites in North America are A. quadrimaculatus (eastern, 

 southern and middle-western States), A. punctipennis (widely dis- 

 tributed), A. crucians (southern and south-eastern coastal area), A. 

 walkeri (eastern area) , and .4 maculipennis freeborni (Pacific coast) . 

 Boyd and coworkers observed that (1) A. quadrimaculatus and A. 

 punctipennis were about equally susceptible to Plasmodium vivax; 

 (2) A. quadrimaculatus was susceptible to several strains of P. falci- 

 parum, while A. punctipennis varied from highly susceptible to re- 

 fractory to the same strains; (3) A. quadrimaculatus was more 

 susceptible to all three species of Plasmodium than coastal or inland 

 A. crucians. Thus A. quadrimaculatus is the most dangerous malaria 

 vector in the United States as it shows high susceptibility to all hu- 

 man Plasmodium. A. pseudopunctipennis distributed from south- 

 western United States to Argentina and A. albimanus occurring in 

 Central America, are but a few out of many anopheline vectors of 

 human Plasmodium in the areas indicated. Host-parasite relation 

 (Boyd and Coggeshall, 1938); malaria vectors of the world (Komp, 

 1948); susceptibility of Anopheles to malaria (King, 1916; Boyd and 

 Kitchen, 1936); epidemiology in North America (Boyd, 1941), in 

 Brazil (Boyd, 1926), in Jamaica (Boyd and Aris, 1929), in Cuba 

 (Carr and Hill, 1942), in Trinidad and British West Indies (Downs, 

 Gillette and Shannon, 1943), in Porto Rico (Earle, 1930, 1939), in 

 Haiti (Paul and Bellerive, 1947), in Philippine Islands (Russell, 

 1934, 1935a), in India (Russell and Jacob, 1942) and in Liberia; gen- 

 eral picture (Russell, 1952, 1952a); mosquito control (Russell, 1952a) 



The time required for completion of sexual reproduction of Plas- 

 modium in mosquitoes varies according to various conditions such 

 as species and strain differences in both Plasmodium and Anopheles, 



