Biology and ecology of European natural enemies of swallow -worts (Vincetoxicum) and the potential for biological control

A biological control program was initiated against two European swallow-worts in North America to minimize their negative effects on native flora and fauna. In manuscript one, populations of Vincetoxicum spp. were surveyed for insect herbivores across Europe to locate new biological control agents and examine herbivore-plant associations. In laboratory studies, larval performance of all herbivores was generally better on the target weeds than V. hirundinaria and are promising as biological control agents. In manuscript two, the preliminary host specificity of H. opulenta was evaluated in quarantine against 34 species. Larvae only completed development on Vincetoxicum although partial larval development occurred on two members of the Urticaceae (nettles). Some non-target plants were oviposited on under no-choice conditions, but eggs were never laid on species supporting larval development. These results strongly imply that H. opulenta is specific to Vincetoxicum. The biology of H. opulenta and its larval feeding impact on Vincetoxicum performance were studied in manuscript three. Larvae develop through five larval instars and overwinter as pupae but pupal diapause is facultative. Damage by two or more larvae was capable of reducing aboveground biomass and reproduction of V. rossicum, but not V. nigrum - most likely because larvae did not inflict similar levels of damage to both Vincetoxicum sp. In manuscript four, the density-dependent effects of leaf herbivory by A. asclepiadis and root herbivory by Eumolpus asclepiadeus were evaluated singly on Vincetoxicum performance. The negative effects of root herbivory on plant biomass increased with density, but leaf herbivory had no effect on Vincetoxicum performance. The results of this study are encouraging for the release of E. asclepiadeus and warrant completing host specificity testing with this insect. However, given that defoliation did not affect Vincetoxicum performance, further evaluation of A. asclepiadis is needed before release is considered. The benefits of larval group feeding in relation to larval performance of the leaf beetle Chyrsolina asclepiadis on Vincetoxicum were evaluated in the last manuscript. The largest benefit of group feeding for C. asclepiadis was enhanced host location rather than larval growth, but it is likely that both work together to improve larval performance