Abstract
Among the factors limiting species distribution,low temperatures play a key role for tropical invasive species in temperate areas. Susceptibility to cold winter conditions has been recognized as the limiting factor in Europe for Tetranychus evansi, an invasive spider mite feeding on Solanaceous plants originated from tropical South America and now present on every continent except Australia. Two genetically distinct lineages of this species were introduced to Europe; one (lineage 1) is widely distributed, while the other (lineage 2) has a limited distribution. Whether this difference corresponds to differences in cold hardiness is evaluated here by assessing phenotypic response of T. evansi to the winter conditions that the mite encounters in the coldest parts of the current invaded area. We designed the thermal regimes to mimic winter conditions, including temperature fluctuations between day and night (L:D 8:16, 12:4 C) and exposed mites to this regime for 5, 10 or 15 weeks. We tested T. evansi from three locations, one from the tropical native area (Piracicaba, Brazil) and two, corresponding to the two introduced lineages, from the temperate invaded area (lineage 1 from Nice and lineage 2 from Perpignan, France). After 5 weeks of treatment, mites from all the locations showed high survival rates but the two introduced populations grew, producing more than one offspring per female. After 10 weeks, survival rates declined for mites from Brazil and Perpignan, but not Nice. After 15 weeks, only the mites from Nice survived and produced offspring. Thus, mites belonging to the widespread lineage 1 exhibit increased cold tolerance suggesting broader adaptability, helping to explain its current geographical distribution.