Reevaluating establishment and potential hybridization of different biotypes of the biological control agent Longitarsus jacobaeae using molecular tools

Evaluation of past and current biological control programs using molecular tools can clarify establishment success of agent biotypes, and can contribute to our understanding of best practice for natural enemy importations. The flea beetle, Longitarsus jacobaeae Waterhouse (Coleoptera: Chrysomelidae) has successfully controlled the weed tansy ragwort, Jacobaea vulgaris Gaertn., in Pacific coastal areas of the USA. A L. jacobaeae biotype introduced in 1969 from Italy is assumed to provide this control. A cold-adapted biotype from Switzerland was also released in 1969 to California, but its establishment was never confirmed. Recent infestations of tansy ragwort into parts of Montana with continental, winter-cold climates prompted introduction of the Swiss biotype in 2002. The Italian and Swiss biotypes cannot be separated morphologically and are able to hybridize in the laboratory. We used amplified fragment length polymorphisms to assess which biotypes established in California, Oregon, and Montana at sites with varying climatic conditions, and whether the biotypes have hybridized in nature. The analysis was based on 216 L. jacobaeae individuals collected from 13 populations in the introduced and native ranges in 2006 and 2007. Clustering and assignment tests showed that the Italian biotype successfully established at all study sites, including those characterized by continental, winter-cold climates. We also found hybrids of the two parental biotypes, which in one study location constituted 47% of the population. Future studies are needed to evaluate whether to release either biotype alone or in combination on new tansy ragwort infestations in winter-cold climates in North America.

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► Amplified fragment length polymorphisms confirm that the original release of the Swiss biotype of Longitarsus jacobaeae in northern California in 1969 did not lead to establishment.
► Italian biotype beetles successfully established at high elevation sites in Oregon and Montana despite significant climatic differences with their area of origin.
► The Italian and recently re-released Swiss biotype beetles hybridize at high elevation sites in Montana and hybrids constituted a surprisingly high proportion of at least one population.