52 Procehdings of Ninth Annual Meeting 



tions, and the degree to which these conditions have not been met 

 measure the extent to which the resuhs have been unreHable. 



PURPOSE OF COUIvECTlONS. 



At this point it is well to examine the purposes of these col- 

 lections to see whether certain of these purposes cannot be met 

 without completely complying with the above specifications. In 

 general the purposes of these mosquito collections is to evaluate 

 in terms of mosquito density the immediate results of the anti- 

 mosquito work and to enable the anti-mosquito chief to trace 

 sources of the mosquitoes which are found on the wing. It has 

 been definitely shown that nearly all species of mosquitoes will 

 move more or less from the area in which they were bred and 

 this fact means that the collections must be made with sufficient 

 frequency to detect the presence of these mosquitoes before they 

 have moved from the point where they were hatched and espe- 

 cially before they have moved far enough to have broken the 

 connection. Perhaps the meaning of breaking the connection of 

 the breeding place needs illucidation. As a brood of mosquitoes 

 emerges it does not escape all at once but the emergence covers 

 a co'nsiderable number of days. Indeed under most conditions 

 the writer believes the first ones to emerge have moved from 

 their breeding places for considerable distances before the last 

 are out. In time, however, all have moved and all evidence of 

 a connection of a swarm and its breeding place has disappeared. 

 In the early stages of this movement there seems tO' exist a con- 

 stantly increasing density from the vanguard of the brood to 

 the breeding place from which the rearguard has not yet moved 

 and in many cases not yet emerged. If the collection stations 

 are sufficiently numerous this increasing density will be obvious 

 by the number of mosquitoes of a certain species caught at each 

 of the different stations and it may very well be that if the 

 source of breeding is within the area itself examination of the 

 collections the following morning will probably locate the source 

 of breeding within a very limited locality within which inspec- 

 tion for breeding places a brood can still be found in process 

 of emergence. If on the other hand the brood has not been 

 bred in the area under control definite evidence of it as an in- 

 vasion will make its appearance and collections of succeeding 

 evenings in the direction of increasing density will surely point 

 to the source from which the invading brood came. 



