Dalmatian toadflax has been a target for biological control in North America since the 1960s. The stem-mining weevil Mecinus janthiniformis was first released in Canada and the western United States in the mid-1990s. Since 2007, a citizen-based monitoring program in Idaho, USA has supplemented data collection to help evaluate the impact of M. janthiniformis on Dalmatian toadflax abundance and assess changes in the surrounding plant community. We monitored and analysed trends in toadflax, weevil, and the plant community abundance following weevil releases at the regional and site level (34 sites) across the state of Idaho, USA. Significant declines in toadflax cover and stem density were recorded across the majority of sites. Weevil populations have established at all release sites. The mechanistic model indicated that the population dynamics of toadflax at our sites are negatively affected by M. janthiniformis abundance. When averaged across the region, 15 years after weevil release, Dalmatian toadflax stem density and cover declined by 93 and 84%, respectively. We observed significant declines in toadflax abundance in over 75% of the sites. Changes to the surrounding plant community following weevil releases were less consistent among sites. At the regional scale we found evidence for an overall increase in average cover of native perennial grasses and other exotic weeds (primarily annual grasses and exotic forbs) but a decline in native forbs.
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We thank the monitoring personnel, Carol Randall, and Paul Brusven for their instrumental role in data collection and anonymous reviewers for the valuable suggestions to the manuscript. We also would like to thank Richard Reardon for his continued support of our research. This research was funded by USDA USFS Special Technology Development Project (STDP) Grant 10-CA-11010000-013 to M.S.
Handling Editors: Mark Schwarzländer, Cliff Moran and S. Raghu.
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Weed, A.S., Milan, J. & Schwarzlaender, M. Analyses of nine years of citizen-based biological control monitoring of Dalmatian toadflax, Linaria dalmatica (Plantaginaceae) in Idaho, USA. BioControl 63, 449–460 (2018). https://doi.org/10.1007/s10526-017-9848-2
- Post-release assessment
- Weed population dynamics