Variation in herbivory within and among plants of Daphne laureola (Thymelaeaceae): Correlation with plant size and architecture

1 Herbivory by noctuid moth larvae (Lepidoptera, Noctuidae) on plants of Daphne laureola L. (Thymelaeaceae) was studied under natural conditions in a south-eastern Spanish montane habitat. The main objective of the study was to determine how size and architectural features correlated with herbivory level (mean percentage leaf area removed by the end of the larval growth season) and herbivore load (mean number of caterpillars recorded per day) both among and within plants. 2 A significant correlation was found between herbivore load and herbivory level of individual plants. Herbivory levels differed widely (range = 0.1-12.8% leaf area) and were considerably smaller than those often used in artificial defoliation experiments. 3 Variation among plants in the incidence of noctuid larvae was directly related to the number of leaf whorls, and inversely to the mean basal diameter of stems. These responses to size and architectural traits may be explained by discrimination by ovipositing females. 4 Within plants, larvae preferentially selected leaf whorls having shorter supporting stems and lower branching orders. Movement costs may be reduced by larvae using plant architectural traits as cues for within-plant food selection. 5 The reasons for and potential implications of the different features used by adult noctuids discriminating between plants and by their larvae selecting leaf whorls are discussed.