Determining the origins of invasive species has important management implications when introduced species become pests, especially when candidate biocontrol agents are specialized on host biotypes. The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), is a European native that was first discovered in North America in British Columbia in 1931. It has since become a major economic pest of brassicaceous oilseed crops. To assess population structure and determine points of origin for North American introductions, we sequenced a 475-bp fragment of the mitochondrial DNA COI gene in 176 individuals from 16 localities from North America and Europe. Eleven haplotypes were found, with one haplotype present in every locality and represented by 71% of all individuals. Nested clade analysis indicated fragmentation, range expansion, restricted gene flow, and long distance dispersal. Analysis of molecular variance (AMOVA) also showed significant population structure and supported an inference of restricted gene flow between populations. These patterns may be explained by two separate introductions to North America. The first introduction was to western North America from source locations likely to have been western or northern Europe, and the second was to northeastern North America from locations, such as Sweden or Russia, that are distinct from the first introduction. At least two females were introduced to western North America, and three to northeastern North America, where the species was recently detected in Quebec.
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