Journal of Chemical Ecology, Vol. 18, No. 7, 1992 CHEMICAL VARIATION WITHIN AND BETWEEN INDIVIDUALS OF Plantago lanceolata (PLANTAGINACEAE) M. DEANE BOWERS 1'* and NANCY E. STAMP 2 University Museum Department of Environmental, Population and Organismic Biology Campus Box 334 University of Colorado Boulder, Colorado 80309 2Department of Biological Sciences University at Binghamton State University of New York Binghamton, New York 13902-6000 (Received August 26, 1991; accepted February 18, 1992) Abstract--Variation in concentrations of leaf nitrogen and iridoid glycosides was examined in replicate plants of five genotypes of Plantago lanceolata (Plantaginaceae) grown in an experimental garden. Nitrogen concentration and iridoid glycoside concentration were affected by leaf age. New leaves had nitrogen concentrations 1.7 to 2.7 times higher than mature leaves. Catalpol concentration was highest in new and intermediate-aged leaves. The concen- tration of aucubin, the biosynthetic precursor to catalpol, was higher in inter- mediate-aged leaves than in mature leaves, in three of five genotypes. Consequently, the proportion of aucubin relative to total iridoid glycosides increased as leaves aged. Concentration of iridoid glycosides was not corre- lated with plant size. Plant genotype significantly affected concentration of nitrogen and iridoid glycosides, as well as plant size. Thus, major indicators of hostplant quality for insect herbivores varied considerably both within and among plant genotypes and individuals. Key Words--Plantago lanceolata, iridoid glycosides, aucubin, catalpol, nitrogen, plant size, plant-insect interactions, chemical variation. INTRODUCTION A population of plants represents a heterogeneous resource for herbivorous insects. Individual plants may vary in their morphology and architecture (Law- * TO whom correspondence should be addressed. 985 00984)331/92/0700-0985506.50/0 91992 Plenum Publishing Colq~oration