THE MOSQUITOES OF THE SOUTHEASTERN STATES 7 
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 the 
larvae per dip in a series of dips. ‘This method is utilized prin- 
cipally in connection with anopheline surveys. The relative impor- 
tance of the area in mosquito production can be expressed numerically 
by multiplying the average number per dip by a factor representing 
the extent of the breeding area (size times percentage of breeding 
surface). The productivity of a breeding place per unit of surface 
can also be determined by the use of cloth nets or screen cages placed 
over the water (29). 
Breeding places may be divided into two general classes, permanent 
and temporary. The two classes frequently intergrade, however, and 
the status of a given area may change over a period of time. Ano- 
pheles and Culex occur typically in the permanent breeding places, 
whereas most Aedes and Psorophora are found in the temporary 
collections of water produced by rainfall, floodwaters, or high tides. 
The status of the breeding places, particularly the permanent ones, 
as to productivity may change greatly during the course of a season 
or from year to year, owing to changes in the amount of aquatic 
growth or flotage, the abundance of natural enemies, and other causes. 
The importance of temporary breeding places of Aedes and 
Psorophora is frequently difficult to determine, because consider- 
able time may elapse between broods. One may visit suspected 
areas repeatedly without finding larvae, and such areas must be 
classified as potential breeding places until more definite evidence is 
obtained. The type of vegetation, especially in salt marshes, is often 
an indicator of the suitability of breeding conditions. Breeding 
occurs on the parts of the marsh that are above the normal daily tidal 
range, and the elevations are indicated by the type of plant growth, 
since many of the plant species are restricted rather sharply by the 
height of the water table and the frequency of tidal coverage. More 
definite information on suspected breeding areas can sometimes be 
obtained from samples of sod taken from dry depressions by scooping 
off a thin layer of topsoil with a small shovel. Samples from differ- 
ent parts of the area are placed in containers and covered with water 
to cause hatching of the eggs, which may begin within a few minutes. 
Glass containers are preferable, as the small larvae are more easily 
seen when these containers are held against the hight. If the sods 
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