Community structure of insect herbivores in a hybrid system: examining the effects of browsing damage and plant genetic variation

Abstract

Abstract. 1. Using three genetic classes of willows,Salix eriocephala,Salix sericea, and their interspecific F1 hybrid, the influence of browsing damage and the importance of genetic class on insect community structure were evaluated.2. Three‐year‐old plants grown from seeds generated from controlled crosses were placed in a common garden after a damage treatment was imposed on them (plants were either left undamaged during the previous winter or they had 50% of the previous year's growth removed). Clipping damage caused large increases in mean shoot length for plants.3. The abundance of eight species of insect herbivores was determined for every plant to evaluate community structure for three genetic classes across the two damage levels. Based onmanova, damage treatment had a modest effect on the relative abundance of herbivores (i.e. their proportional representation). In contrast, dramatic differences were detected among genetic classes for relative abundance; in cases where damage treatment influenced relative abundance of herbivores, the importance of genetic class was at least 20‐fold greater than that of damage treatment. No interaction between genetic class and browsing treatment was detected for community structure.4. The weak response of the herbivore community to clipping damage, contrasted to the large response to genetic class, was very surprising because mean shoot length was greatly altered by damage treatment. These findings, coupled together with previous research, suggest that plant genetic differences can act as the primary basis for herbivore community structure, while the effects of browsing may not be as common.