THE MOSQUITOES OF THE SOUTHEASTERN STATES 17 



an index of density, but they may be unreliable because of variations 

 in the rate of collection under different conditions as well as in the 

 mechanical limitations to the numbers of mosquitoes that can be 

 collected in a given time. 



TRAP COLLECTIONS 



For most species the suction type of light trap (fig. 6) is very 

 useful for obtaining samples of the mosquito population, for records 

 of comparative abundance, and, in control areas, for immediate in- 

 formation on the occurrence of outbreaks. In connection with con- 

 trol work the traps are placed at strategic places throughout the area 

 and are usually operated every night. For other purposes the traps 

 may be run on a schedule of one or more nights each week. The 

 traps should be hung in an open space with the light itself 5 or 

 6 feet from the ground, and they should not be placed in the 

 immediate vicinity of a street light. 



The number of mosquitoes caught per night frequently runs into 

 the hundreds or even thousands, and many other kinds of insects 

 are found in the killing bottles. Under these conditions the task 

 of separating and identifying the material is considerable, especially 

 when the specimens are badly damaged or wet. Species not taken 

 while biting appear in the light-trap collections, and it has been 

 found that the different bloodsucking species are not attracted to 

 the lights equally. Over a series of nights the writers' trap-collection 

 records have shown more variation than the biting records, which, 

 of course, are the more accurate index of annoyance. From a large 

 series of trap collections made in Florida only an occasional specimen 

 of Aedes aegypti has been obtained, and the numbers of Culex quin- 

 quefasciatus and C. nigripalpus appear to be very small in compari- 

 son with the amount of breeding occurring in the neighborhood of 

 the traps. This also seems to be true to some extent of Anopheles 

 quadrimaculatus. The trap records, therefore, cannot be relied on 

 as an index of density for these species. 



Boxes of various sizes and shapes, having the inside painted black 

 or lined with black cloth, have been employed to attract mosquitoes, 

 particularly anophelines and the house Culex, as a daytime resting 

 place. They are placed in corners of rooms or in sheltered places 

 outside the houses. In the morning, after the mosquitoes have en- 

 tered, the open end of the box is covered and the specimens are 

 killed, for counting, by fumigation or by placing the box in the sun. 



Animal-baited traps have been used for collecting mosquitoes and, 

 in the Tropics at least, have been employed for determining densities 

 of anopheline species that do not remain in accessible shelters during 

 the daytime. A number of such traps have been described. 



COLLECTIONS OF LARVAE 



The collecting of larvae in connection with mosquito-control sur- 

 veys has for its main purpose the locating of breeding places and 

 the determination of their importance. Some information may be 

 obtained as to the comparative abundance of different species from 

 the identification of a large series of collections. Rough estimates 

 of the relative abundance of a species can be obtained by counting 



109619 — 39 2 



