Post‐introduction evolution in the biological control agent Longitarsus jacobaeae (Coleoptera: Chrysomelidae)

Rapid evolution has rarely been assessed in biological control systems despite the similarity with biological invasions, which are widely used as model systems. We assessed post‐introduction climatic adaptation in a population of Longitarsus jacobaeae, a biological control agent of Jacobaea vulgaris, which originated from a low‐elevation site in Italy and was introduced in the USA to a high‐elevation site (Mt. Hood, Oregon) in the early 1980s. Life‐history characteristics of beetle populations from Mt. Hood, from two low‐elevation sites in Oregon (Italian origin) and from a high‐elevation site from Switzerland were compared in common gardens. The performance of low‐ and high‐elevation populations at a low‐ and a high‐elevation site was evaluated using reciprocal transplants. The results revealed significant changes in aestival diapause and shifts in phenology in the Mt. Hood population, compared with the low‐elevation populations. We found increased performance of the Mt. Hood population in its home environment compared with the low‐elevation populations that it originated from. The results indicate that the beetles at Mt. Hood have adapted to the cooler conditions by life‐history changes that conform to predictions based on theory and the phenology of the cold‐adapted Swiss beetles.