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During the nineteenth century, there was an enormous growth of knowledge in the field of bacteriology. Much of the expansion resulted from discoveries by German bacteriologist Robert Koch and French chemist Louis Pasteur . The two scientists are considered the founders of modern medical bacteriology and were instrumental in demonstrating the relationship between exposure to bacteria and specific human and animal diseases. These diseases involved causative agents, or pathogens, such as bacteria, which would interact with human and animal hosts and induce illness caused by infection or toxicity. The illnesses were collectively classified as “communicable diseases” since they could be transmitted from one host to another.

It has been known for centuries that numerous species of insects are vectors of human diseases and causative agents of agricultural devegetation. The scientific community recognized this problem, and numerous researchers attempted to discover insecticides that were potent to insects yet relatively innocuous to humans, animals, and vegetation. Prior to the discovery of the insecticidal property of DDT in 1939 by Paul Hermann Müller, inorganic, arsenic-based insecticides were most commonly developed because of their effectiveness in controlling insects. These insecticides, which were initially used during the latter half of the 1800’s, however, were found to be very toxic to humans and other mammals. Other common insecticides utilized prior to the 1940’s were the inorganic fluorinated compounds plus organic-based nicotine, pyrethrum, and derris compounds. These substances, however, had limited application and insufficient permanent effect because of their instability in the environment.