BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 33 
Bollworm 
The bollworm is one of the most difficult cotton insects to control. 
Timeliness of application and thorough coverage with the insecticide 
throughout the period of infestation are especially important in con- 
nection with this pest. DDT and toxaphene are both effective against 
the bollworm, but DDT alone will not control certain other cotton 
pests and aphids increase after its use. 
In Texas a dust containing 10 percent of DDT and sufficient ben- 
zene hexachloride to give 2 percent of the gamma isomer controlled 
bollworms better than 20 percent of toxaphene or 5 percent of DDT 
plus benzene hexachloride to give 3 percent of gamma. 
In 1948 serious outbreaks of this insect occurred in Texas, Oklahoma, 
New Mexico, and Arizona. Large acreages were dusted with the new 
organic insecticides, and satisfactory results were usually obtained 
when they were applied at the proper time. 
Cotton aphid 
Since aphid infestations often follow the use of insecticides for the 
control of other cotton insects, all dusts for use on cotton should con- 
tain a toxicant for aphids. Experiments in several States indicate 
that benzene hexachloride or parathion will control cotton aphids if 
applied at the proper time. Evening applications of benzene hexa- 
chloride were more effective than morning applications. A dust con- 
taining benzene hexachloride, DDT, and sulfur gave satisfactory 
control of the cotton aphids as well as boll weevils, bollworms, and 
spider mites. Toxaphene applied against weevils and bollworms also 
controlled cotton aphids. 
In the tests with concentrated sprays in Mississippi, excellent control 
of cotton aphids was obtained with tetraethyl pyrophosphate at 0.1 
pound and adequate control with benzene hexachloride at 0.3 pound 
of the gamma isomer per acre. The sprays were applied at 3 : 30 in 
the afternoon, when the temperature was 80° F. and the wind velocity 
12 miles per hour. 
Pink bollworm 
DDT continues to be the best insecticide for control of the pink 
bollworm. Dusts should be applied every week in sufficient quantities 
to give 1.5 to 3 pounds of technical DDT per acre. Benzene hexa- 
chloride and sulfur should be included to prevent build-up of other 
cotton insects and mites. Thorough coverage of the cotton plants is 
important, and when the dusts are applied by airplane the swaths 
should not be more than 45 feet wide. 
Although the pink bollworm is now confined to four southwestern 
States and Florida, the results of survival tests in Texas in 1948 em- 
phasize the importance of continuing strong measures to prevent its 
spread. In the winter of 1947-48 the pink bollworm survived a tem- 
perature of —6° F., and moths emerged in south Texas as long as 
12y 2 months after the larvae entered hibernation. 
Salt-marsh caterpillar 
The worst outbreak of salt-marsh caterpillars ever known occurred 
in the Salt Kiver Valley of xVrizona in the fall of 1948. Much of 
