Lower genetic diversity and decreased genetic differentiation in populations of western flower thrips across an invaded range

Abstract Colonizing populations of alien invasive species are often unstable due to their small population size, ongoing gene flow, and ongoing adaptation to local conditions. These processes should lead to molecular signatures at the population level. However, temporal changes in genetic patterns after introduction are rarely examined. The western flower thrips (WFT), Frankliniella occidentalis (Pergande), is a globally invasive pest of vegetables and ornamental crops. Early colonized populations in China exhibited a strong population structure reflecting different invasion sources. Here, we re-examine this pattern after ten years. Over this period, the number of alleles has declined significantly and strong population genetic structure found early in the invasion stage has been lost. A high level of gene flow between both geographically close and distant populations was identified. The reduced allele number and loss of population structure might reflect both ongoing gene flow and ongoing control measures to suppress populations. Our results emphasize the importance of continuing to manage gene flow among invaded areas to limit the exchange of alleles that might facilitate further adaptive changes following invasion.