| An Italian biotype of the ragwort flea beetle, Longitarsus jacobaeae Waterhouse (Coleoptera: Chrysomelidae), originating from a Mediterranean climate has been the most effective biological control agent against the invasive tansy ragwort (Jacobaea vulgaris) in Pacific coastal areas of the U.S. The spread of tansy ragwort into new environments, including high-elevation areas in northern Idaho and northeastern Montana, has prompted the re-introduction of a cold-adapted biotype of the flea beetle from Switzerland. While the biotypes are morphologically identical they differ in the phenologies, presumably as adaptation to different climatic conditions in their native range.;Establishment patterns of the two beetle biotypes across the Pacific Northwest were investigated using molecular tools. The Italian biotype was found in a wide range of environments including those at higher elevations, characterized by continental, winter-cold climates. Hybrid individuals between Italian and Swiss beetles were also detected at a study site in Montana. Reciprocal transplant and common garden field and laboratory experiments were used to test whether Italian beetles at a high-elevation location on Mt. Hood, Oregon, underwent rapid evolution in response to the significantly reduced growing season at that location. The results indicate that the beetles at Mt. Hood genetically adapted to the cooler conditions in less than 30 years, with shifts in life history and morphological traits that conform to predictions based on models, empirical studies and the phenology of the known cold-adapted Swiss beetles. Finally, to assess the potential impact of hybridization on biological control of tansy ragwort, phenological and fitness characteristics of F1 and F2 reciprocal hybrids between Italian and Swiss L. jacobaeae were measured in the laboratory. Most measured traits showed intermediate values for the two hybrid lineages with some maternal effects. Most importantly, both hybrid lineages had a higher fitness than the Italian parent, or in one hybrid lineage both parents. |
