The treatment may be applied with garden-type pressure sprayers or with power equipment. The surfaces where flies concentrate (such as garbage cans, animal houses, and so on) should be thoroughly covered. The spray should also be applied on the inside of the establishment that is to be protected. It is preferable to paint the doors and window screens, because spraying them would be wasteful. Although DDT is an excellent control for flies, it is recommended that sanitary practices, such as the elimination of breeding places, the disposal of garbage, and screening, be continued. DDT is slow in its action, and several hours' exposure is frequently required to kill flies. So, if the fly population is high, a reduction as high as 95 percent may leave enough flies to create a problem.

The use of DDT in conjunction with pyrethrum in sprays and the aerosol bomb has already been discussed. The pyrethrum is included mainly to increase the speed of knock-down, but the DDT is the principal killing agent.

Fleas are usually considered an occasional or accidental pest of man. In this country this is largely true, but in many parts of the world many houses are infested with the human flea (Pulex irritans L.), and they are found in the clothing and on the body of man much as they occur on our pets. Bubonic plague and endemic typhus are caused by fleas.

Our researchers found that DDT is highly effective for controlling fleas both on the person and in buildings. As a spray it may be employed as a residual treatment (in a manner similar to that already described for flies and mosquitoes) , but dusts containing 10-percent DDT are also recommended. The DDT dust or spray should be thoroughly applied to the floor and furnishings or to the infested soil. If possible, the source of the infestation should be determined and eliminated. If pets cause the trouble, as they generally do, they and their bedding should be treated with a suitable flea powder. DDT can be used safely on dogs, but it should not be used on cats. When infestations occur on the person, the clothing should be thoroughly dusted the same as for body lice.

DDT destroys fleas on rats. Early work on this problem was undertaken by the Bureau of Entomology and Plant Quarantine station at Savannah, Ga., and by the Menard, Tex., station in cooperation with the Texas State Board of Health. The United States Public Health Service has also studied the problem extensively. The studies indicate that it may be possible to control murine typhus, which is transmitted by the rat flea (Xenopsylla cheopis (Rothsch.).

Bedbugs fortunately do not carry disease but they are common and widespread pests. They are easily and effectively controlled with DDT.

After the usual preliminary laboratory tests procedures, A. H. Madden of the Orlando laboratory treated the bedstead, springs, and heavily infested mattress of a bed with about 3 ounces of a 5-percent DDT spray. For a year after the treatment he tried to reinfest the bed with bugs from the laboratory colony, but the efforts were unsuccessful all the bugs died within 48 hours. While such experiments were still in progress, thousands of beds in military establishments at Orlando were treated by the Army as an experiment. For at least 6 months after the treatment, not a single bedbug was found alive in the beds.

The small insects called sand flies in the United States include the Culicoides. They are commonly referred to as punkies or, because of their small size, no-see-ums. The true sand flies (Phlebotomus) are of little importance in this country, but in many parts of the world they are major pests, mainly because of certain diseases that they transmit.

DDT can be employed as a residual treatment applied to the inside of buildings, stone fences, screens, and other favorite resting places for controlling the true sand flies. The method of treatment is essentially the same as for mosquitoes. The number of sand flies and punkies in this country can be reduced by the use of airplane sprays, fog machines, and by treating the screens and the inside of houses.

Pyrethrum is not a new insecticide, but some new uses for it have been found, and its toxicity to insects has been increased by combining it with materials that by themselves are not toxic an action that is termed activation or synergism. In 1940 C. W. Eagleson, of the Dallas, Tex., laboratory of this Bureau demonstrated that sesame oil used in pyrethrum fly sprays greatly increased the activity of this insecticide.

Other materials have been developed for use in fly sprays and for other types of insecticide materials that contain pyrethrum. Among these is N-isobutylundecylenamide, which, when tested in combination with pyrethrum, was found to increase the effectiveness of the insecticides from 10 to 100 times. This development was the basis for the first louse powder recommended for use by the armed services. The powder, known as MYL formula, contained 0.2 percent of pyrethrins (the active principle of pyrethrum extract), 2 percent of N-isobutylundecylenamide, 2 percent of 2,4-dinitroanisole (for killing louse eggs), 0.25 percent of Phenol S (a pyrethrum stabilizer or antioxidant) in pyrophyllite dust.

The MYL powder, the most effective treatment known at the time, was widely used by the armed services for the control of lice attacking man, and as a general-purpose insecticide. Although it was replaced by DDT, the research leading to the development of the pyrethrum-synergist combination insect powder was important and further emphasizes the potential value of synergists for pyrethrum. A number of other promising synergists have been tested for possible use in fly sprays and other treatments involving the use of pyrethrum. Among these, two of the most effective are piperonyl cyclohexenone, and piperonyl butoxide.

Experiments with pyrethrum, even before DDT was available, had shown that this insecticide has good residual killing properties. Excellent control of bedbugs for several weeks after treatment was demonstrated by making residual treatments of pyrethrum sprays. The use of N-isobutylundecylenamide increased the activity of the residual treatment against this insect. Investigations also showed that pyrethrum applied as a residual treatment is effective against other insects including adult mosquitoes, houseflies, and cockroaches; and certain synergists greatly increase the effectiveness and lasting properties of such treatments.