Effect of the Lichen Chemicals Atranorin and Vulpinic Acid upon Feeding and Growth of Larvae of the Yellow-striped Armyworm, Spodoptera ornithogalli1

Abstract

Solutions of atranorin and vulpinic acid, chemicals occurring in the wolf lichen Letharia vulpina (L.) Hue and other lichens, were coated onto leaves of broccoli Brassica oleracea var. italica Plenck. Feeding by larvae of the polyphagous yellow-striped armyworm Spodoptera ornithogalli Guenee in choice tests was reduced on vulpinic acid coated leaves. Growth was slowed on atranorin coated leaves in a no-choice situation in comparison to larvae feeding on control (isopropanol coated) leaves. That these chemicals were effective at the low concentrations used (atranorin <0.03% and vulpinic acid <0.6% of leaf dry weight) and yet naturally occur at much higher concentrations (atranorin approaches 1% and vulpinic acid approaches 6% dry weight) indicates they may be potent antiherbivore compounds responsible in part for the apparently low herbivore pressure upon lichens containing them.