Toxicity and Deterrency of Sesquiterpene Lactones and Chromenes to the Corn Earworm (Lepidoptera: Noctuidae)

Abstract

Encelia farinosa Gray (Asteraceae: Heliantheae), a common shrub of the Sonoran desert, contains both sesquiterpene lactones and chromenes. Chloroform extracts of E. farinosa leaves were deterrent to larvae of Heliothis zea (Boddie) in choice tests, but farinosin, a eudesmanolide sesquiterpene lactone from E. farinosa, was not. Five sesquiterpene lactones from different Asteraceous genera were examined for their effect on the relative growth rate (RGR) of H. zea at 0.1% fresh weight in an artificial diet. Only dchydroleucodin, a guaianolide sesquiterpene lactone from Artemisia tridentata spp. vaseyana, reduced growth. Three closely related chromenes (precocene 1 and 2 and encecalin) were examined for their effects on survivorship (SR) and RGR of H. zea at five different concentrations. Precocene 1 and 2 exhibited the greatest activity on survivorship and growth rates, whereas encecalin was less active.