Response of Five Insect Species to a Botanical Insecticide, Rhodojaponin III

Abstract

Rhodojaponin III is a grayanoid diterpene compound with insect antifeedant and insecticidal properties. The compound was isolated from the Chinese insecticidal plant Rhododendron molle (G. Don) and tested against five species of agricultural and stored-grain insects in laboratory and greenhouse bioassays. At LC50 and EC50 (the effective concentration for 50% growth inhibition). rhodojaponin III was 198 to 218 times more active for fall armyworm, Spodoptera frugtperda (J. E. Smith), larvae than for tobacco budworm, Heliothis virescens (F.), larvae. Results of tests with potted plants indicated that rhodojaponin III at 150 ppm reduced the plant damage index from 96 to 13% for S. frogiperda , from 99 to 2% for Colorado potato beetle, Leptinotarsa decemlineata (Say), and from 72 to 55% for greenbug, Schizaphis graminum (Rondani). Against adults of the confused flour beetle, Tribolium confusum (Jacquelin du Val), 50 ppm rhodojaponin III in flour caused 89% mortality and totally inhibited fecundity. We obtained similar results with an ethyl acetate extract of the dried flowers of R. molle .