One for example: From the fine University of Minnesota http://ipmworld.umn.edu/chapters/ware.htm Rest of post is quoted from the above site: At the beginning of World War II (1940), our insecticide selection was limited to several arsenicals, petroleum oils, nicotine, pyrethrum, rotenone, sulfur, hydrogen cyanide gas, and cryolite. And it was World War II that opened the Chemical Era with the introduction of a totally new concept of insect control chemicals--synthetic organic insecticides, the first of which was DDT. .... ORGANOPHOSPHATES Organophosphates (OPs) is the currently used generic term that includes all insecticides containing phosphorus. Other names used, but no longer in vogue, are organic phosphates, phosphorus insecticides, nerve gas relatives, and phosphoric acid esters. All organophosphates are derived from one of the phosphorus acids, and as a class are generally the most toxic of all pesticides to vertebrates. Because of the similarity of OP chemical structures to the "nerve gases", their modes of action are also similar. Their insecticidal qualities were observed in Germany during World War II in the study of the extremely toxic OP nerve gases sarin, soman, and tabun. Initially, the discovery was made in search of substitutes for nicotine, which was heavily used as an insecticide but in short supply in Germany.