io6 N. J. Mosquito Extermination Association 



small larvae of the fresh-water swamp mosquito (Aedes sylves- 

 tris) everywhere in the quiet water. The water fell with suffi- 

 cient rapidity to destroy the breeding on the better-drained por- 

 tions of the valley, but enough escaped from the undrained 

 sections to make trouble in June. 



To the north and west of this valley lay successive ranges 

 of low mountains beginning at an elevation of about 400 feet 

 and increasing rapidly in height, with gaps leading only to higher 

 elevations and sparse population. To the south and east lay two 

 ridges of low mountains with an extreme height of a little over 

 400 feet, and with deep gaps leading out upon level or rolling 

 plains of low elevation and dense population. 



On June '15 a series of daylight collections madqi from Newark 

 to and across the upper Passaic valley showed the fresh-water 

 swamp mosquito in constantly increasing numbers from East 

 Otange to Hatfield swamp, the nearest piece of swampland in 

 this valley, and in rapidly decreasing numbers until the collecting 

 ceased on the north shore of the valley. From East Orange to 

 Hatfield swamp as the crow flies is about 7 miles, in the course 

 of which the two before-mentioned ridges rear their crests. By 

 the roadway followed in making the collections the distance was 

 about 10 miles. 



Beginning on June 20, series of collections were made on all 

 sides of the upper Passaic River valley. These collections show 

 a rapidly disappearing density to the north and west, a more 

 slowly diminishing density to the south and east, and the greatest 

 density in the areas facing the gaps which lead from this valley 

 to the south and east. 



Inasmuch as the fresh-water swamp mosquito by this date had 

 had time to effect its distribution: (i) the low and rapidly de- 

 creasing density to the north and west may be taken to indicate 

 that movement in that direction was slight; (2) that the more 

 slowly decreasing density to the south and east may be taken to 

 indicate that the movement in the direction was more pro- 

 nounced ; ( 3 ) that the greater and more slowly decreasing den- 

 sity in the areas which face the gaps leading from this valley to 

 the south and east may be taken to indicate that the principal 

 movement occurred through these gaps. 



