Zoological Studies

Vol. 39 No. 3, 2000

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

Simon J. Yu

Department of Entomology and Nematology, University of Florida, Gainesville, FL 32611, USA

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.

Key words: Juvenile hormone, Ecdysone, Cytochrome P450, Fall armyworm, Allelochemicals.

*Correspondence: Tel: 1-352-392-1901. Fax: 1-352-392-0190. E-mail: sju@gnv.ifas.ufl.edu