52 THE REPOET OF THE No. 36 



communities within reach of flights from the salt marshes (see map). Before 

 the flight of certain salt marsh species was recognized many local efforts were dis- 

 credited by the influx of these far-flying species. It is, therefore, necessary to 

 find some way of determining not only the species that are bred within the pro- 

 tected area, but also the species which breeding entirely outside may invade and 

 annul the effect -of local work. 



Without doubt the most accurate way of determining these points is that type 

 of a seasonal study of mosquitoes on the wing which will enable the operator to map 

 the mosquito fauna at short intervals throughout one or more summer seasons. It 

 is true that a person having long and wide experience with mosquito control can 

 make a rather accurate guess at the nature of the mosquito trouble in a specified 

 area by a study of possible mosquito breeding places within and without of the said 

 area. His forecast is, however, merely a shrewd guess and may go very wide of the 

 mark. 



In the collection of data necessary to the preparation of the mosquito dis- 

 tribution maps a limited number of stations must be selected in such a fashion that 

 some definite idea of the conditions throughout the infested area may be obtained. 

 In order that the collection results may be comparable the places selected must be 

 essentially similar, especially as regards cover and light or the difference between 

 them must be evaluated, which is always a difficult matter. The portion of the 

 body from which the collections are made must be the same, and the collector whose 

 body does not attract mosquitoes must be eliminated. Collections must be made at 

 a time of the day when as nearly all species are active as possible. It may be 

 necessary to determine this time by running a set of trial collections covering all 

 liours of the day and night. For the purpose of comparing one collection with. 

 another the temperature, moisture and wind conditions during the period when each 

 area-wide collection is made must be recorded and eventually more or less accurately 

 evaluated. 



The mosquitoes must be caught and killed without crushing or rubbing them 

 in order that accurate identification of them may be made. The results of each 

 general collection, stated as so many mosquitoes of each species per selected unit of 

 time should be set down on a topographic map of the area and the nature of the 

 weather conditions noted on the same sheet. 



If properly prepared this map will afford a picture of mosquito conditions at 

 the time when the collection was made and if properly interpreted will show 

 whether the collection methods should be modified and will indicate what changes 

 should be made. 



If the number of specimens of each species caught appears to be perfectly 

 irregular in distribution the results may be attributed to emergence from local 

 breeding. If on the other hand, there is evident an area in which certain species 

 appear in greatly increased numbers which grow larger from some point in the 

 area to its boundaries, it is safe to assume, that an invasion of mosquitoes breeding 

 outside the protected area is occurring. If there should appear specimens of a 

 species, the known habits of which would seem to preclude breeding within the area, 

 invasion of that species would be clearly indicated. 



Whenever the charts show the presence of invasions, they must be traced at 

 once to the source from which they come. The method employed in these tracings 

 will depend upon the species concerned. When dealing with the salt marsh or the 

 fresh water swamp mosqu ./o, the work may be done during daylight by means of an 

 automobile, but when dealing with the house mosquito, the collections must be made 

 during a period beginning about dusk and ending less than one hour later. In 



