ABSTRACT
Efforts to control agricultural pests probably evolved in parallel with cultivation techniques. Early methods included manual removal of weeds and insects, rigorous hoeing to prevent weed growth, and the use of traps for animal and insect pests. The first chemical controls to be used against agricultural pests were the arsenical compounds. In 1910, Ehrlich discovered that arsphenamine was an effective treatment for syphilis. This was the first
chemotherapeutic agent for a bacterial infection and the first example of a structure-activity relationship. It opened the door to the entire field of chemical control of both infections and of pests. Paracelsus had introduced the use of inorganic arsenicals, notably arsenic trioxide (As
O
, white arsenic), into medicine in the sixteenth century but its use was limited by its extreme toxicity. Ehrlich’s discovery revived interest in these compounds. In 1824 the Colorado potato beetle was discovered east of the Rockies and its eastward spread accelerated the search for an effective control. As
O
was found to be effective and came into widespread use. Other arsenicals were developed, including Paris green (copper arsenite) which is still used as slug bait. Being a heavy metal, arsenic is persistent in the environment, the significance of which was not appreciated when it was being widely used.
