Zoological Studies

Allelochemical Induction of Hormone-metabolizing Microsomal Monooxygenases in the Fall Armyworm

Simon J. Yu (2000) Juvenile hormone lll was oxidized by midgut microsomes pre- pared from larvae of the fall armyworm, Spodoptera frugiperda (JE Smith). The oxidase is membrane bound, requires NADPH for activity, and is inhibited by carbon monoxide and piperonyl butoxide; it therefore is a typical microsomal monooxygenase, hereafter referred to as JH lll oxidase. Feeding the allelochemicals, indole-3- carbinol and β-naphthoflavone, to larvae caused 188% and 105% increases, respectively, in JH lll oxidase activity as compared with the controls. lnduction of microsomal ecdysone 20-monooxygenase activity by allelochemicals was further studied in this insect. Dietary monoterpenes [(+)-pulegone, (+)-limonene, β-myrcene, (+)-camphor, (+)-camphene,  α-terpinene,  Γ-terpinene], sesquiterpenes (farnesol, nerolidol), indoles (harmine), coumarins (coumarin), methylenedioxphenyl compounds (safrole, isosafrole, myristicin, piperonyl butoxide), and ketohydrocarbons (2-tridecanone) all stimulated ecdysone 20-monooxygenase activity in larvae from 53% to 234% as compared with the controls. Harmine was the most potent inducer among those tested. Azadirachtin when administered orally or by injection had no effect on ecdysone 20-monooxygenase activity in fall armyworms.