Benzene Hexachloride

This material, investigated by the French and British before it was tested in this country, is equal to DDT in many respects. Research at Orlando in 1943 and 1944 showed that the crude product containing 12 percent of the gamma isomer (the gamma isomer is the most toxic form of this material) was about as effective as DDT on body lice when used at a concentration of 10 percent in pyrophyllite. When applied as a residual spray against flies and mosquitoes, its properties resembled that of DDT, but it generally was more rapid in its action. It was also found to be quite effective as a mosquito larvicide but less so than DDT. E. R. McGovran, in work at Beltsville, found that the gamma isomer is actually about eight times more toxic than DDT to flies when used as a space spray.

The insecticide is effective against chiggers when dusted or sprayed on infested soil or vegetation. As little as 5 pounds to the acre of the crude material will give practically complete control of the mites for several weeks after treatment. Sulfur, which was formerly recommended for this purpose, requires at least 100 pounds an acre to produce the same results. DDT was found to be relatively ineffective.

Benzene hexachloride is also effective against fly maggots, for which DDT is generally unsatisfactory. When prepared as a benzene emulsion containing 0.1 to 0.25 percent of benzene hexachloride and sprayed on animal carcasses, it completely destroyed the maggots present.

These brief accounts of results with benzene hexachloride show that it is a potent insecticide. It has, however, an undesirable and persistent odor, a serious draw-back in controlling insect pests of man.

Benzyl Benzoate and Other Mite Killers

Among the most annoying pests of man in the United States are small mites (Eutrombicula and related genera), commonly known as chiggers or red bugs. The first or larval stage will attach itself to man in a manner somewhat similar to a tick and cause extreme local irritation and, sometimes, secondary infections. In certain parts of the world, especially in Burma and some of the Pacific islands, similar mites transmit a serious disease called tsutsugamushi disease.

Early in 1942 A. H. Madden, of the Orlando laboratory, investigated materials and methods of protecting individuals from chiggers. He found that dimethyl phthalate, one of the insect repellents, applied as a barrier about 1 inch wide to all openings in the clothing, was an effective treatment. The chemical was utilized effectively by our military personnel through further research by the United States of America Typhus Commission, United States Army. The only objection to dimethyl phthalate was its lack of persistence when treated clothing got wet. Dibutyl phthalate, first tested by the Australians, was also a good mite treatment, but results with this were somewhat erratic against the chiggers in this country.

Consequently, further research was undertaken at the request of the Typhus Commission of the Army to find more persistent materials. F. M. Snyder, another colleague, tested more than 5,000 materials; among them he found a number of effective miticides. One of the most practical was a commercially available product, benzyl benzoate. Clothing dipped into a 5-percent water emulsion of benzyl benzoate gave complete protection when freshly treated and was effective even after two or three launderings. The treatment became standard.

A skin disease known as scabies and sometimes as 7-year itch is caused by the human itch mite (Scarcoptes scabiei Deg.). It is a common ailment, especially among school children; but under wartime conditions, when people are often closely crowded, epidemics may break out among adults. Various forms of sulfur have been used for it, without much success.

Benzyl benzoate was known to be a good treatment for scabies and was rather widely used in Europe even before the war. In the development of louse control preparations, as previously discussed, benzyl benzoate was included. The preparation, when diluted at the rate of one part of concentrate to five parts of water and thoroughly applied ( I to 3 ounces) to the entire body, has given complete control of the itch mite infestation in a single treatment. The treatment is indicated to be more effective than other types of preparations containing 10-percent benzyl benzoate possibly because the benzocaine aids in destroying the mites and eggs.

Ticks cause severe local irritation, and transmit certain diseases, among them relapsing fever and spotted fever. Methods of protecting the individual from ticks are not entirely satisfactory, but some progress has been made on this problem. H. O. Schroeder of the Orlando laboratory and C. N. Smith of the Savannah, Ga., laboratory found that clothing sprayed with dimethyl phthalate, Indalone, Rutgers 612, or benzyl benzoate at the rate of about 6 to 7 ounces per suit would provide almost complete protection from the "seed" ticks the first stage. Against the nymphal stage, the control was about 90 percent, but only about 60 percent reduction in attachment was obtained against grown ticks.