[Extract] Piperonyl butoxide (PBO) contains the methylenedioxyphenyl moiety, a molecule found in sesame oil and later named sesamin, and thus is classified as a member of the methylenedioxyphenyl group of chemicals. In 1947, it was semisynthesized from safrole, the principal component of camphor oil (Knowles, 1991; Tozzi, 1998). Its molecular formula is C19H300S; it has a molecular weight of 338.4 g/mol. The chemical structure is shown in Figure 205.1. PBO is a colorless to pale-yellow liquid and is moderately stable in that it is resistant to hydrolysis, oxidation, and exposure to sunlight (Kidd and James, 1994). Manufacturers include MGK and Prentiss and Johnsan (Tozzi, 1998). Since its discovery, and since pesticide resistance has emerged as a problem, PBO has been frequently used as an insecticide synergist, in over 1700 insecticides (USEPA, 2002).