1918 ENTOMOLOGICAL SOCIETY. 53 



dealing with other less well known species, it may be necessary to determine the 

 itime of day when the study can be successfully made. In any case the kind of 

 weather, the time of day and the type of cover under which the species being studied 

 may be caught must be determined. 



Tracing invasions of salt marsh species are done very quickly with an auto- 

 mobile by starting in uninfested territory close to the infested area and collecting 

 at regular distances — say, 0.5 of a mile to 2 miles — until the mosquito zone has 

 been traversed and uninfested country found on the other side ; this collection to be 

 followed by a similar one pursued in a line at right angles to the first. 



Two assumptions are, of course, necessary to the success of this plan, one of 

 which is that the mosquitoes may be collected in daylight and the other that the 

 direction of greatest density indicates the source of the brood. The collections are 

 made in as ^nearly similar places as possible, especially as regards the character of 

 the growth, and the relative number present is determined by using two small 

 cyanide tubes and catching specimens 'as rapidly as possible for a definite period of 

 time, then reckoning the catch on the basis of so many per minute. 



In actual practice whenever the study began on the first appearance of the 

 brood, these assumptions were found to be correct and many broods have in this 

 manner been traced to their places of origin. At least three important results 

 followed the discovery and use of this method, the first was the finding of immense 

 breeding areas in the Hackensack Valley salt marsh in sections hitherto thought 

 to be free of breeding, the second was the uncovering of inefficiency in the control 

 of salt-marsh breeding on certain especially dangerous areas, and the third a 

 determined and apparently successful effort to eliminate the breeding places thus 

 discovered. 



The methods found to be successful for the fresh water swamp mosquito 

 migrations are essentially the same. 



It became necessary to find the source of a brood of the house mosquito 

 (C. pipiens) which in spite of effort to control local breeding continued to infest 

 North Elizabeth and Union County. It was quickly found that no progress could 

 be made by day collections and that a difference in the hour when the collections 

 were made gave such a difference in the number caught that determination of 

 density by serial collections covering several hours was impracticable. Accordingly, 

 a sufficiently large number of inspectors were furnished by Union and Essex 

 Counties to cover a line extending through North Elizabeth to and through South 

 Newark to the sewage-charged salt marshes, each man collecting for fifteen minutes 

 at three stations, one-quarter of a mile apart from each other, between 8.00 p.m. 

 and 9 p.m. The following evening in the same manner a line from the marshes 

 running at right angles to the first was collected. In this instance the weather of 

 the two evenings was sufficiently similar to render the results comparable, but 

 generally it would be better to have enough inspectors to collect both lines at the 

 same time. 



A careful study of the collections showed a zone of house mosquitoes extending 

 from North Elizabeth to the Ebling section of the Essex County salt marsh, a 

 distance of at least 2.5 miles, with practically steadily increasing density as the 

 marsh edge was approached. 



Examinations of the marsh, which was heavily charged with sewage, showed 

 enormous numbers of C. salinarius and C. pipiens with small numbers of A. 

 sollicitans and A. cantator in larval and pupal stages. The question has been 

 raised as whether supposed house mosquitoes were not really salinarius. Un- 

 doubtedly both C. pipiens and C. salinarius were component portions of the zone, 



