1917] Some Recent Advances in Mosquito Work 215 



trouble from that area. This method of tracing broods of salt 

 marsh mosquitoes was first tried in 1913 and the results were so 

 satisfactory that it has been used constantly since that time. 



In making a study of this sort, the usual plan is to drive to a 

 point where the brood has been reported. From this point, 

 collections are made outward along lines running to the north, 

 west, south and east until no further specimens can be taken, 

 or until the marsh from which the mosquitoes came has been 

 reached. This will, without doubt reveal the direction of the 

 source of the brood, unless the mosquitoes have been out 

 long enough to lose their connection with the marsh from which 

 they came. When the marsh from which the brood came, 

 has been reached, some idea of the part from which it came 

 can be had by running a collection line along the edges and 

 discovering the point where the mosquitoes are most abundant. 

 In most cases the place of breeding will be found nearest this 

 point, but in others this process will offer little clue, for a heavy 

 growth of trees may attract sufficient numbfers to give a false 

 impression or the direction of the wind may have produced 

 concentration at a distant point. Nevertheless the determi- 

 nation of density gives a point of departure and is worth while 

 when dealing with the problem of finding the pupal skins on a 

 large area of salt marsh. 



In running these collection lines the purpose is to determine 

 the density of the mosquito fauna. It is, therefore, necessary 

 to organize each collection on some sort of a unit basis, and in 

 order to eliminate the serious interference of local conditions 

 to make all collections in as nearly similar situations, especially 

 as relates to cover, as possible. The whole series of collections 

 is usually made within the limits of a single day. Starting 

 in the morning about 8:00 A. M., collections along the first 

 line are made. At each point the collector gets out of the 

 machine, enters the type of growth selected and using two 

 cyanide tubes catches as many specimens as possible in a 

 limited period — say 15 minutes. He then reckons his catch 

 in terms of so many specimens of the species concerned per 

 minute. The distance between stations depends upon the 

 area to be covered. When dealing with a small area the 

 intervals are short, say, anywhere from 34 to 1 mile, but when 

 dealing with an issue that covers a large area the distances 

 range from 2 to 5 miles. 



