EMODIN IN BUCKTHORN: A FEEDING DETERRENT TO PHYTOPHAGOUS INSECTS

Abstract
Emodin, a mixture of anthraquinones, occurs in the Rhamnaceae and functions as a deterrent to foliage-feeding insects. There was little attack on foliage of Rhamnus alnifolia in wild stands compared with associated species of woody plants. Anthraquinones extracted from foliage of R. alnifolia were similar to purchased emodin in thin-layer chromatographic and infra-red spectroscopic analyses. Quantities of emodin in foliage samples were high in May, declining to low levels in August. Leaf powders, leaf extracts, and purchased emodin all showed feeding deterrent activity when mixed with artificial diets and assayed with gypsy moth larvae. Purchased emodin showed similar activity when sprayed on foliage of small cherry trees and assayed with eastern tent caterpillar larvae.