Other chlorinated hydrocarbons, such as chlordane, aldrin, and heptachlor, which are effective against the boll weevil, are ineffective against the bollworm. Their use alone where bollworms are a problem may result in increased infestations of the latter. In those areas they should be used in mixtures with DDT.

Dieldrin is ineffective against the bollworm at the dosage ( 0.15 to 0-25 pound per acre) that kills boll weevils. At a higher dosage, 0-5 pound per acre, it is effective but, to lower costs, when boll weevils and bollworms occur simultaneously, DDT should be added and the lower boll weevil dosage applied.

In experiments conducted in 1945, we found that DDT in xylene emulsions applied at rates of 0.8 and 1.6 pounds of DDT per acre, and at a total volume of 3 gallons per acre at each application, gives satisfactory control of bollworms. Because no satisfactory spray material for the boll weevil had been developed at that time, the discovery was not considered highly important. Growers still required dusting equipment to control the boll weevil, and DDT could be applied as a dust for bollworm control, using this equipment.

With the development of toxaphene for boll weevils, more effort was expended to develop spray applications for all cotton insects. Experimental work in 1948 and 1949 developed spray emulsions for this purpose. They have come into common use on many cotton farms. The emulsions are applied as low-volume sprays through ground machines and by airplane. DDT applied as an emulsion gives as good or better bollworm control than if the same quantity is applied as a dust. Its use in spray mixtures with other insecticides, which will control boll weevils and other insects, has become popular. Sprays may be applied under weather conditions in which the effective application of dust materials would be impossible.

K. P. EWING is an entomologist in the Bureau of Entomology and Plant Quarantine. He was graduated front Mississippi Agricultural and Mechanical College and has been in the Bureau since 1920. In 1933 he was placed in charge of a new laboratory of the division of cotton insect investigations at Port Lavaca, Tex.; in 1939 he became head of the division's new laboratory in n Waco, Tex. The laboratory received the Superior Service Award of the Department of Agriculture in 1949.

Vegetable weevil.

Squash vine borer.

Colorado potato beetle.