80 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



tus) of those of filariasis and dengue fever. It is only through 

 a combination of circumstances that these insects are effective 

 transmitters. These conditions are: the association with man 

 and a predilection for his blood, abundance, comparative lon- 

 gevity, and consequent repetition of blood-meals at intervals, 

 and finally, practically continuous breeding, so that individuals 

 are always present to act as intermediary hosts of the parasites. 

 Thus the chain in the life-cycle of the parasite is never broken. 



The relation of the different species of Anopheles to the 

 transmission of malaria seems never to have been considered 

 in this light. It was, however, brought out in an interesting 

 manner in a paper on mosquito-control in the Panama Canal 

 Zone, read by Mr. Jennings at the recent meeting of the Asso- 

 ciation of Economic Entomologists. Mr. Jennings pointed 

 out that the different species of A nopheles of that region have 

 widely different habits. Investigation of the role of these differ- 

 ent species in the transmission of malaria, by inducing them 

 to suck the blood of malaria-carriers, showed that the species 

 {Anopheles, albimanus] which throve most about settlements, 

 and was most persistent in entering houses and obtaining 

 blood, was the principal factor in malaria transmission, no less 

 than 70 per cent of this species developing the parasites. 

 Mr. Knab said that in commenting on Mr. Jennings's paper 

 he pointed out these facts and in addition gave further evi- 

 dence of the close association of A. albimanus with man, im- 

 parted to him by Mr. Jennings in conversation. 



It appears that this species is absent from those parts of the 

 upper Chagres River which are uninhabited and that the 

 reason is that this mosquito not only prefers, but probably 

 needs, human blood. Mr. Knab said that his remarks before 

 the Economic Entomologists had been met by the assertion 

 of Mr. Schwarz that the absence of .4. albimanus from the 

 upper Chagres had nothing to do with the absence of man, 

 b ; 'twas due wholly to the lack of suitable breeding-places. 

 Mr. Knab stated that Mr. Schwarz was certainly in error 

 and that there were plenty of suitable habitats for the larvae 

 of A. albimanus, at least in parts of the uninhabited region 

 under consideration. 



