88 NORTH AMERICAN DIPTERA 



causative organism, although other warm blooded animals may take the 

 place of man. If the mosquitoes essential for the development of the 

 organisms causing the disease were destroyed the disease would dis- 

 appear entirely and it is because of this that such vigorous steps have 

 been taken to stamp out mosquitoes in various parts of the world. The 

 complete destruction of all disease carrying mosquitoes is scarcely pos- 

 sible but it has been demonstrated in the Panama Canal Zone that they 

 can be kept under control to such an extent that the diseases they carry 

 are no longer a serious menace to residents of the region. It is now so 

 well known that the construction of the Panama Canal was made possible 

 only by the control of mosquitoes that no more than mention of the fact 

 need be made here. 



Malaria is still a common disease in many parts of the United 

 States. ]\Iany of us think of it as a tropical or subtropical disease, but 

 nothing could be further from the truth. Malaria has raged at one 

 time or another over rather large areas of the northern states and 

 may do so again if patients suffering from the disease in its active 

 stage should be bitten by our native Anopheles mosquitoes and they 

 have the opportunity of developing and injecting the ])rotozoan causing 

 the fever into the blood stream of uninfected persons. 



The North American Anopheles known to transmit the disease are 

 quadrimaculatus, maculipennis, punctipennis, crucians, and atropus in 

 the United States, alhimanus, pseudopunctipennis and quadrimaculatus 

 in Mexico, and alhimanus and tarsimaculatus in Central America and 

 the West Indies. The last three species named for the United States 

 are not considered important vectors of the disease. 



The causative organisms of Malaria are Plasmodium vivax for ter- 

 tian, P. malarice for quartan, and P. falciparum for the pernicious type. 

 Tertian is our commonest type, being approximately three times as 

 prevalent as the other two combined, while the pernicious form is almost 

 twice as prevalent as the quartan. 



An idea of the essential part played by insects which act as inter- 

 mediary hosts for parasites causing human diseases, may be obtained 

 from a brief outline of the life cycle of Plasmodium vivax. The organ- 

 ism passes an asexual stage in man, developing and multiplying in the 

 red corpuscles, causing them to enlarge. In a little less than two days 

 the trophozoites are mature, having absorbed the contents of the cell 

 and the term schizont is now applied to them. These divide into from 

 15 to 24 merozoites and are discharged into the blood stream by ruptur- 

 ing of the cell wall. The cycle now begins over again and the same 

 process is repeated, but after a time certain of the merozoites develop 

 into male (microgametocytes) and female (macrogametocytes) which 



