Invasion Genetics of the Western Flower Thrips in China: Evidence for Genetic Bottleneck, Hybridization and Bridgehead Effect

The western flower thrips, Frankliniella occidentalis (Pergande), is an invasive species and the most economically important pest within the insect order Thysanoptera. F. occidentalis, which is endemic to North America, was initially detected in Kunming in southwestern China in 2000 and since then it has rapidly invaded several other localities in China where it has greatly damaged greenhouse vegetables and ornamental crops. Controlling this invasive pest in China requires an understanding of its genetic makeup and migration patterns. Using the mitochondrial COI gene and 10 microsatellites, eight of which were newly isolated and are highly polymorphic, we investigated the genetic structure and the routes of range expansion of 14 F. occidentalis populations in China. Both the mitochondrial and microsatellite data revealed that the genetic diversity of F. occidentalis of the Chinese populations is lower than that in its native range. Two previously reported cryptic species (or ecotypes) were found in the study. The divergence in the mitochondrial COI of two Chinese cryptic species (or ecotypes) was about 3.3% but they cannot be distinguished by nuclear markers. Hybridization might produce such substantial mitochondrial-nuclear discordance. Furthermore, we found low genetic differentiation (global FST = 0.043, PF. occidentalis should focus on preventing it from spreading from the putative source populations to other parts of China.

西花蓟马（Frankliniella occidentalis (Pergande)）是一种入侵性昆虫，也是缨翅目（Thysanoptera）昆虫中经济重要性最高的害虫。该虫原产于北美，2000年首次在中国西南地区的昆明被发现，此后迅速扩散至中国多个其他区域，对温室蔬菜与观赏作物造成了严重危害。在中国防控这一入侵性害虫，需要深入了解其遗传组成与迁移模式。本研究借助线粒体COI基因（mitochondrial COI gene）与10个微卫星标记（其中8个为新开发的高多态性微卫星标记），对中国14个西花蓟马种群的遗传结构及种群扩张路径展开了调查。线粒体与微卫星数据均显示，中国境内西花蓟马种群的遗传多样性低于其原产地种群。本研究发现了两种此前已报道的隐存种（或生态型）：二者的线粒体COI基因序列分化程度约为3.3%，但无法通过核标记将其区分，这种显著的线粒体-核基因组冲突可能由杂交事件导致。此外，本研究检测到较低水平的遗传分化（全球FST=0.043，P<0.001），研究结果表明西花蓟马的防控应重点阻断其从推定的源种群向中国其他区域扩散。