CHEMICAL VARIATION AND DEFENSE OF ENCELIA-FARINOSA

Chemical analysis of leaves from 12 different localities of Encelia fa rinosa (including var. phenicodonta and var. radians) collected on the peninsula of Baja California (Mexico) revealed the presence of variou s chemotypes that differed with regard to the concentrations of chrome nes and sesquiterpene lactones. Localities of E. farinosa collected in the northern part of Baja California were characterized by high conce ntrations of the chromene encecalin (up to 252 mu mol g(-1) dry wt.), whereas the sesquiterpene lactone farinosin was not detected. Localiti es of E. farinosa collected at the southern tip of the peninsula lacke d encecalin, but were shown to accumulate farinosin (up to 85 mu mol g (-1) dry wt.) instead. On the mainland of Mexico, as well as in Arizon a (U.S.A.), farinosin concentrations varied from 18 to 44 mu mol g(-1) dry wt. for 10 different localities analyzed. Chromenes were not dete cted or present only in minor amounts (up to 13 mu mol g(-1) dry wt.), when compared to the samples from northern Baja California. Chemical variation within localities was small when compared to variation betwe en different localities. Accumulation of encecalin and aridity seem to coincide at least on the peninsula of Baja California, as localities of E. farinosa that receive the least amount of rainfall contained the largest amounts of encecalin in their leaves. Leaves of E. farinosa t hat contained sufficiently large amounts of either encecalin or farino sin were both detrimental to neonate larvae of the polyphagous pest in sect Spodoptera littoralis as shown by addition of the respective crud e leaf extracts to artificial diet. Possible advantages of the observe d intraspecific chemical variability of E. farinosa with regard to ada ptation by generalist insect herbivores are discussed.