Theses and Dissertations Collection

Classical biological control of weeds is an important tool for weed management practiced around the world. However, it is not always successful. Examining historical records of biocontrol efforts would be an alternative approach to understand biocontrol agent and target weed traits correlations with success. The second chapter of this thesis is a review examining life history traits of biocontrol agent and target weed life history traits associated with biocontrol establishment and impact using the 5th edition of ‘Biological Control of Weeds: A World Catalogue of Agents and their Target Weeds’ and other reports of biological control agents and target weed traits. This analysis showed that both biocontrol agent and target weed life history traits influenced the success of biological control programs, with the traits of agents more important than those of the weed. The analysis is intended to inform biological control practitioners of the importance agent and weed life history traits for establishment and successful control of weeds. Chapter 2 also revealed that biocontrol candidate agents are typically exposed to test plant species grown in nutrient-rich homogenous soil, but this could influence the susceptibility of herbivory that are adapted to special soil types, for example nutrient-poor metal-rich serpentine soil. Therefore, in the third chapter of this thesis, I tested these hypotheses in our system, the invasive weed, Lepidium draba L. (Brassicaeae), several nontarget species related to this weed and a biological control candidate, the stem and petiole gall-forming weevil Ceutorhynchus cardariae Korotyeav (Coleoptera: Curculionidae). Results showed that native serpentine soil influenced C. cardariae herbivory. Our data show that native species confamilial with the target restricted to specialized soil types may be at less risk of herbivore attack than predicted based on tests conducted in horticultural soil.