A Comparison of Various Approaches for Evaluating Potential Biological Control Agents Using Insects on Lythrum salicaria

The selection of biological weed control agents that become successfully established and provide good control has proven difficult. During a program aimed at controlling Lythrum salicaria, a perennial Eurasian plant invading North American wetlands, various approaches developed for prioritizing potential biocontrol agents were utilized to rank nine insect species. In addition, species were ranked according to characteristics of successful agents identified by the analysis of past biological weed control programs. Different approaches produced contradictory results. Therefore, species selected for host-specificity screening and release were ranked according to their impact on plant performance, feeding niche, and distribution. Hylobius transversovittatus, a root-boring weevil, was given the highest priority, followed by two leaf-feeding beetles, Galerucella calmariensis and Galerucella pusilla. Currently existing protocols for selecting the most promising candidates from an existing species pool are not satisfactory. Carefully planned release and follow-up studies on the effect of single and multiple species herbivory as well as type of herbivore feeding on plant performance and population dynamics can eventually improve the success of biological weed control.