Dehydrothalebanin: A source of resistance from Glycosmis pentaphylla against the citrus root weevil Diaprepes abbreviatus

Roots of a citrus relative, Glycosmis pentaphylla (orangeberry), were shown to inhibit, the growth and survival of larvae of the citrus root weevil Diaprepes abbreviatus. Roots of G. pentaphylla incorporated into the diet of D. abbreviatus increasingly inhibited the growth of neonate larvae with increased concentration of roots, while roots from citrus rootstocks produced little inhibition. The diet-incorporation assay was used to guide fractionation of an active acetone extract of G. pentaphylla roots. Three major fractions from silica open-column liquid chromatography were active, and these were purified using semipreparative normal-phase HPLC. A single active HPLC subfraction was isolated from each of the three Liquid chromatography fractions, and two active compounds were isolated and identified by GC-MSD. GC-MSD and NMR identified one compound as the amide dehydrothalebanin B, and the other was identified by GC-MSD as dieldrin, a chlorinated hydrocarbon insecticide whose origin in our samples is uncertain.