Paris green and oil (kerosene, Diesel, and fuel oils) were widely used before DDT became available for controlling larvae of the malaria mosquitoes. Oil was also the standard method of controlling the various Culex, Aedes, Psorophora, and related mosquitoes. One to 2 pounds of paris green per acre of water surface was generally needed for adequate anopheline larvae control. C. C. Deonier and assistants of the Orlando laboratory demonstrated that DDT in dust form (using 1 to 2 percent of DDT in talc) was more effective when applied at the rate of 1 pound to 20 acres. For routine treatment, however, DDT in dust form is recommended at the rate of 1 pound to 10 acres.

Furthermore, when dissolved in kerosene or fuel oil and properly applied, 1 quart of oil containing 5 percent of DDT was shown to be equally as effective as 20 to 25 gallons of oil that did not contain DDT. The great savings in cost of materials, transportation, and labor for the DDT treatments are therefore readily apparent. For routine control operations against various kinds of mosquitoes 5 quarts of a 1-percent DDT solution of fuel oil applied as a fine mist is recommended for each acre of breeding area. Ordinary garden-type pressure sprayers and even hand pressure sprayers have been found satisfactory for the small breeding areas. Where large areas involving hundreds of acres are to be treated, and if the DDT is not applied by means of airplanes, power units may be employed.

DDT may be used in ways other than dusts or oil solutions. The DDT emulsion concentrate already mentioned in connection with the control of lice was found useful in mosquito control. This concentrate (or several modifications of this formula) when diluted with water so that the finished spray will contain 1 percent or less of DDT was found to be a very effective and satisfactory treatment. The recommended dosage of 0.1 pound of DDT per acre meant that less than one-half pint of material had to be transported for each acre of larval breeding area.

Airplanes, formerly used extensively for applying paris green dusts, are very useful for applying DDT sprays. Good control of the Anopheles and most of the other kinds of mosquito larvae can be obtained with 1 to 2 quarts of fuel oil containing 5 percent DDT per acre applied with special spray equipment.

Studies by the Tennessee Valley Authority, the armed services, and the Bureau of Entomology and Plant Quarantine have shown that excellent control of Anopheles mosquito larvae can also be obtained with fine mist sprays by applying as little as one-half pint per acre when a 20-percent DDT solution is employed. This means that an airplane that can carry 1,000 pounds can treat 2,000 acres with one load.

DDT has provided new and strikingly effective means of controlling adult mosquitoes. There are three general methods of attack on adult mosquitoes with DDT. The methods were first investigated by A. W. Lindquist, J. B. Gahan, B. V. Travis, and others of the Orlando laboratory. First, and perhaps the most important, is the use of this insecticide as a residual or surface spray. Never before has an insecticide been employed in this way for controlling adult mosquitoes, although R. Wiesmann of Switzerland had shown that flies could be controlled thus. The spraying of the inside of buildings, under bridges, inside hollow logs, or even the vegetation itself with DDT leaves a deposit of DDT that will kill mosquitoes which rest in such places for weeks or even months later.

Many laboratory tests were run in 1943 with many types of DDT sprays. Different rates of application were used on various surfaces. The tests showed that some differences existed in regard to the effectiveness of the DDT on different kinds of surfaces, but in general a single treatment at the rate of 1 gallon of 5-percent spray for each 1,000 square feet remained effective for many months. After the laboratory tests, field experiments were run in Arkansas in 1943 and 1944. The inside walls of barns, toilets, chicken houses, bridges, and other places where Anopheles mosquitoes rest were treated with 5-percent DDT solutions. Kerosene or the water emulsion already mentioned were tested. As long as 5 months after one treatment there was a reduction of about 99 percent in the number of mosquitoes resting in the buildings.

A mosquito cannot transmit malaria until about 2 weeks after it has fed on a person having the disease. If the houses and other resting places of mosquitoes in the vicinity of human habitations are treated, the mosquitoes will be killed sometime during the 2-week period. This break in the chain is the key to the success of DDT in the control of malaria and other diseases transmitted by mosquitoes. It is sometimes difficult to realize how important this one development is to people everywhere, but the fact is that malaria and other important mosquito-borne diseases cause more than 100 million cases of illness and many deaths each year.

Another new method of utilizing DDT involves spraying large areas to kill the adult mosquitoes as well as the larvae. Airplane equipment was used, and it was shown that adult mosquitoes as well as the larvae could be controlled. When epidemics of mosquito-borne diseases occur, this method permits immediate control of the disease by killing the already infected mosquitoes in the area; the destruction of the larvae prevents a rapid increase in the mosquito population.

Adult mosquitoes can also be controlled with equipment that can be used on the ground. In fact, in the first tests with DDT for killing adult mosquitoes outdoors, hand dusters and sprayers were used. Because of the success of those early tests, investigations of various types of equipment to disperse DDT fogs and sprays for mosquito control were undertaken. V. K. LaMer of the National Defense Research Committee, working with Randall Latta, developed special fog machines, which are proving effective and practical for controlling mosquitoes, sand flies, gnats, and various other annoying insects.

A third way to use DDT against adult mosquitoes consists of sprays and aerosols for use inside houses and other confined space to give immediate but temporary control of the insects present. Pyrethrum has been widely used in household sprays. DDT added to such a spray was found to increase its killing power for flies and mosquitoes. Ordinary refined kerosene containing DDT and pyrethrum makes an effective space spray for mosquitoes and for general household use. The method is not to be confused with residual or surface application.

DDT was found useful in the pyrethrum aerosol bomb, which was developed by L. D. Goodhue and W. N. Sullivan. In order to add the 3-percent DDT to the Freon aerosol, the amount needed for general use, the formula had to be modified. After testing many preparations, the Orlando scientists and those at Beltsville developed formulas.

The common housefly carries filth and disease. Sanitary practices and the use of screens, sprays, and other methods give a fair degree of control against the insect. Too often, however, available control measures are not judiciously followed. Army and Navy personnel realized the danger of flies. Dysentery, a disease spread by flies, was a major problem in certain war theaters, and the presence of many flies lowered morale.

Fortunately DDT is a powerful weapon. Early in 1943, even before we had heard that Wiesmann of Switzerland had previously employed DDT residual treatments for fly control, Mr. Lindquist had shown DDT treatments to be effective for several months when tested under laboratory conditions. Practical tests at dairies and military establishments in Florida showed that a 5-percent DDT-kerosene spray, thoroughly applied at the rate of 1 gallon for each 1,000 square feet of surface, would reduce flies by more than 95 percent as long as 4 months after treatment. Since that time DDT has been widely employed in oil solutions, emulsions, wettable powders, and dusts. The amount of DDT to apply varies with the length of the fly season, climate, and the type of surface to be treated, but it is generally recommended that 1/2 to 3 ounces for each 1,000 square feet of surface be used in solutions containing from 1 to 5 percent of DDT.