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Dalmatian and yellow toadflax, Linaria dalmatica and L. vulgaris, are exotic weeds in North America, and their classical biological control has been improved by the establishment of seed-feeding (Rhinusa antirrhini) and stem-mining (Mecinus janthinus and Mecinus janthiniformis) weevils. Here, we evaluated the complex of hymenopteran parasitoids attacking these weevils in Colorado. Ten species were identified of the genera Neocatolaccus, Eurytoma, Pteromalus, Brasema, Telenomus and Bracon. Neocatolaccus tylodermae was the most abundant parasitoid of M. janthinus, M. janthiniformis and R. antirrhini. This is the first report of N. tylodermae attacking the weevil genera Mecinus and Rhinusa feeding on the genus Linaria. [ABSTRACT FROM AUTHOR]

A majority of the plant species that are introduced into new ranges either do not become established, or become naturalized yet do not attain high densities and are thus considered ecologically and economically unproblematic. The factors that limit these relatively "benign" species are not well studied. The biotic resistance hypothesis predicts that herbivores, pathogens and competition reduce growth and reproduction of individual plants and so suppress population growth of non-native species. We explored the effect of insect herbivory and surrounding vegetation on growth and fitness of the non-native biennial plant Verbascum thapsus (common mullein) in Colorado, USA. Mullein is widespread in its introduced North American range, yet is infrequently considered a management concern because populations are often ephemeral and restricted to disturbed sites. To evaluate the impact of insect herbivores on mullein performance, we reduced herbivory using an insecticide treatment and compared sprayed plants to those exposed to ambient levels of herbivory. Reducing herbivory increased survival from rosette to reproduction by 7%, from 70-77%. Of plants that survived, reducing herbivory increased plant area in the first year and plant height, the length of the reproductive spike, and seed set during the second year. Reducing herbivory also had a marked effect on plant fitness, increasing seed set by 50%, from about 48,000 seeds per plant under ambient herbivory to about 98,000 per plant under reduced herbivory. Our findings also highlight that the relationship between herbivory and performance is complex. Among plants exposed to ambient herbivory, we observed a positive relationship between damage and performance, suggesting that, as predicted by the plant vigor hypothesis, insect herbivores choose the largest plants for feeding when their choice is not restricted by insecticide treatment. In contrast to the strong effects of experimentally reduced herbivory, we found that cover of other plants surrounding our focal plants explained relatively little variation in performance outcomes. Overall, we found that herbivore-induced impacts on individual plant performance and seed set are substantial, and thus may help prevent this naturalized species from becoming dominant in undisturbed recipient communities. [ABSTRACT FROM AUTHOR]