The Chemistry of DDT

by H. L. HALLER and RUTH L. BUSBEY

OLD PEOPLE in Germany used to say that moths would not attack woolens dyed green. The saying was untrue, but it influenced the investigations that led to the discovery of DDT as an insecticide. Born thus of a fiction, the almost miraculous killer of disease-carrying insects is still the center of a good deal of fiction.

In a few years it has excited the imagination of scientists and laymen alike and rightly, for it is effective against a wider variety of agricultural pests than any other synthetic insecticide heretofore tested; it gives control of those history-old scourges, the body louse, the mosquito, and the fly; and, wonderful to relate, its effect lasts, sometimes as long as a year. Evidence of the tremendous interest in DDT is that more than 2,000 articles have appeared in scientific, trade, and general magazines and newspapers about it, almost all of them acclaiming its merits. A colleague of ours, R. C. Roark, in 1944 compiled a 12-page list of publications that had appeared on the subject since 1874; in the next few months, so great was the flood of writing on it, he had to revise and expand the list twice.

This tremendous interest in one compound created one near-fiction involving DDT, the impression in some minds that few studies have been made to find chemicals effective for the control of injurious insects. Actually, the use of chemicals to control insect pests has been going on for centuries. The earliest insecticides were arsenicals and sulfur. Systematic attempts to control insects were first made about 1865 when, in this country, paris green, which was available as a paint pigment, was used to destroy the Colorado potato beetle. Paris green was so effective that for many years it was the most widely used agricultural insecticide; even today our farmers and gardeners use about 4 million pounds of it a year. In 1892 lead arsenate was developed for use against the larva of the gypsy moth, a serious foe of shade and forest trees. Lead arsenate was found to be effective against many insect pests; its use has continued to increase, and about 80 million pounds of it were used in 1945.

Actually, also, the modern era of the development of new insecticides began about 1910. Investigators here and abroad became interested in how insecticides kill and emphasized the importance of physical characteristics, such as wetting and spreading of sprays on foliage and insects. At that time some of the more important insecticides and fungicides, the arsenicals, nicotine, pyrethrum, derris, lonchocarpus, lime-sulfur, and bordeaux mixture, had been known a long time and some of them had been in use. Much of the effort since then has been devoted to the study of these and related products in order to discover their range of usefulness; to increase their efficiency; and to find more powerful substitutes, safer to man, domestic animals, and plants.

The studies leading to the discovery of DDT as an insecticide can in a measure be traced back to some research initiated about 30 years ago. In 1915 the Bayer dyestuffs company in Leverkusen, Germany, undertook an intensive investigation of chemicals that might be suitable for mothproofing wool. The early investigations were influenced by the saying that woolens dyed green are not attacked by the clothes moth. Investigations proved the saying to be erroneous. Further investigation showed that the early green dyestuffs had a bluish shade, and in order to produce better greens it was the practice to add a yellow dye. For this purpose, Martins Yellow, 2,4-dinitro- 1 -naphthol, was commonly used. Tests showed the compound to be effective against the clothes moth. For practical use, however, it had faults, primarily color and lack of fastness. The findings were followed by the testing of many synthetic organic compounds against the clothes moth and led to the development of several products; one group was named "Eulans."

The "Eulans" achieved some commercial success and stimulated interest in mothproofing agents by other chemical manufacturers. Soon after the "Eulans" were made commercially available, J. R. Geigy, S. A., in Switzerland started a research on mothproofing agents. After an extensive series of investigations, the Geigy firm developed and marketed a class of mothproofing agents known as "Mitins." The studies in the Geigy organization on mothproofing agents were expanded to the testing Of compounds against other insects and led to the discovery of DDT.

Probably the most accurate account of the introduction of DDT into this country is given by Victor Froelicher, an official of the Geigy company in this country. In an article in Soap and Sanitary Chemicals, he wrote: "In August 1942, we received from Switzerland 100 pounds each of `Gesarol' spray, containing 5 percent active ingredient, and 'Gesarol' dust, containing 3 percent active ingredient. At about the same time, we received news that Maj. A. R. W. De Jonge, American Military Attache at Berne, Switzerland, had shown great interest in our new lousicidal composition called 'Neocid,' which contained the same active ingredient as the 'Gesarol' products. It was indicated that 'Neocid' had great significance in controlling the typhus-carrying body louse.