Leaf biomechanical properties and the densities of herbivorous insect guilds

Summary This study investigated relationships between leaf biomechanical properties and the densities of their associated insect herbivores. The herbivorous insects associated with 18 co‐occurring plant species were sampled over 16 months. Biomechanical properties of new and mature leaves of each plant species were measured using punching, shearing and tearing tests. Significant variation in leaf biomechanical properties was found among plant species, and between new and mature leaves. Total insect density was significantly negatively correlated with work to tear (r = −0·43, P < 0·05) and work to shear (r = −0·70, P < 0·01). Although chewing insect density was significantly correlated with punch strength of mature leaves, sucking insect density was not. While studies of herbivory often include measures of leaf punch strength, this mechanical trait may indicate resistance to chewing insects but not sucking insects. We conclude that leaf biomechanical properties are influencing the functional composition of herbivorous insect assemblages in this system.