80 ANNUAL REPORTS OF DEPARTMENT OF AGRIC1 LITKK. 1952 
during daylight hours. However, at dusk and for an hour or t wo after 
dusk the mosquitoes migrate freely. At Mich time they may fly into 
the treated area and cause severe annoyance before they come in con- 
tact with i reated surfaces. 
Several Insecticides Effective in Controlling Fire Ants 
The imported fire ant, found in the Southern States, particularly 
Alabama and Mississippi, is an annoying pest of man and animals 
and is also destructive to certain agricultural crop-. Surveys during 
the past 3 year- have shown that the pest is also present in Georgia, 
Louisiana, Texas, Florida, South Carolina, Tennessee, and Arkansas. 
Further research has been conducted to develop improved methods 
for emu rolling the pest. ( Ihlordane emulsions containing 0.37 percent 
chlordane applied to individual mounds at the rate of about 3 gallons 
per average mound having a diameter of 3 feet, will usually destroy 
the colony, although follow-up treatment- with about 1 gallon for each 
surviving colony may be required. When applied on an area basis 
2 to 4 pounds an acre of chlordane will usually eliminate all colonies. 
Research under way indicates that aldrin is equally as effective as 
chlordane and that dieldrin may be about twice as effective as 
chlordane. 
INSECTS AFFECTING ANIMALS 
New Approach to Screw-Worm Control Being Tested in the Field 
In efforts to develop methods for eradicating screw-worms from 
restricted areas, particularly in the Southeastern States, an entirely 
new approach to inject control is being investigated. Laboratory in- 
vestigations during the past *_! years have demonstrated that when 
pupae of the screw-worm are exposed to 5,000 roentgens ^\' X-rays, 
flies thai subsequently emerge are not seriously affected from the 
standpoint of activity and length of life but they are incapable of 
reproducing. 'The sterile male- will mate with normal females and 
Buch mated females deposit infertile eggs, A significant point is thai 
the female- of this insect male only mice even when mated to X-ray 
Bterilized male-. It has been shown by tests in laboratory cages that 
the sterile males compete successfully with normal male-. Tests on 
caged screw-worm population- containing lo normal female-. L0 nor- 
mal males, and 90 sterile males show that approximately 90 percent of 
the females lay infertile eggs. This is in line with the percentage of 
sterile eggs that would result from chance, assuming all male- are of 
equal vigor. 
Preliminary studies on natural screw-worm occurrence have indi- 
cated thai the average number present during the winter month- is 
relatively Iom and that it might be economically feasible to rear, treat 
to cause sterility, and release enough flies to start with a ratio of 1" 
sterile flies to I naturally occurring wild fertile fly. 
In view of these encouraging results in the laboratory, investiga 
tion- are now underway In the lie Id to determine if t he release of large 
numbers of sterile flies in an area will cause female flies t<> lay c;:e> 
w Inch do not hatch. 
