Differential Levels of Insect Herbivory in the Field Associated with Genotypic Variation in Glucosinolates in Arabidopsis thaliana

Glucosinolates are commonly found in Arabidopsis thaliana and its crucifer relatives, which are known for their role in defense against insect herbivory. In a common garden experiment, we assessed genotypic variation in glucosinolates in A. thaliana and evaluated the association between this chemistry and both plant damage and fitness. Specifically, glucosinolate concentrations were directly associated with damage levels and inversely associated with fitness. These results are contrary to the general expectation that enhanced chemical defense should result in decreased insect herbivory. As the measured insect community in this field trial was dominated by specialist herbivores, this positive relationship between glucosinolates and herbivory agrees with previous observations that glucosinolates (or their hydrolysis products) attract specialist insects. In addition, glucosinolate diversity in this common garden appeared to affect herbivore damage levels. For example, genotypes that contained alkenyl glucosinolates had higher mean damage levels than those that contained hydroxyalkyl glucosinolates. Results suggest that genotypic variation in glucosinolates may be a major factor in determining plant utilization patterns by insect herbivores in the field.