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The newly introduced mosquito Aedes japonicus has expanded from its original range in Northeastern Asia to 29 US states (including Hawaii) plus Canada and northern Europe. Our objectives were to test an earlier hypothesis of multiple introductions of this species to the Northeastern US and evaluate putative temporal changes in genetic makeup. Using a panel of seven microsatellite loci, we confirmed the existence of two abundant genetic forms in specimens originally collected in 1999-2000 (F(ST) value based on microsatellite data = 0.26) that matches the disjunctive distribution of mitochondrial haplotypes. To examine the distribution of the two genetic 'types' across Pennsylvania we created a fine-scale genetic map of Ae. japonicus using 439 specimens collected from 54 Pennsylvania counties in 2002-2003. We also made direct comparisons between collections in 1999-2000 and new collections made in 2004-2005 obtained from the same areas in the northeastern US. We observed that the strong association between mtDNA haplotype and microsatellite signature seen in 1999-2000 had weakened significantly by 2002 across Pennsylvania, a trend continued to some extent in 2004-2005 in PA, NJ, and NY, indicating that once easily distinguishable separate introductions are merging. The two expanding genetic forms create a complex correlation between spatial and genetic distances. The existence of multiple introductions would be obscured without sampling early and across time with highly polymorphic molecular markers. Our results provide a high-resolution analysis of the spatial and temporal dynamics of a newly introduced disease vector and argue that successive introductions may be a common pattern for invasive mosquitoes.

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In September 2019, destruction of a Vespa mandarinia Smith 1852 nest was reported for the first time in North America in Nanaimo, British Columbia, Canada. In December 2019, the Washington State Department of Agriculture also confirmed the first detection of an adult specimen of V. mandarinia in the United States, in Whatcom County, Washington. Vespa mandarinia is the largest hornet species and is a known predator of several insects, including the European honey bee (Apis mellifera) (Hymenoptera: Apidae) (Linnaeus, 1758). The establishment of V. mandarinia in North America poses a serious threat to apiculture, and this species is considered an actionable quarantine pest. Here we report details of the first detection of this species in the United States and use genetic sequence data obtained from five specimens across the globe to estimate differences in origin of the Canadian and U.S. detections. The full mitochondrial genomes of four V. mandarinia specimens representing different geographic locations were sequenced and compared with an existing reference genome. A maximum likelihood tree using 13 protein-coding regions from mitochondrial DNA suggests that the Canada and U.S. specimens are from two separate maternal lineages. A large-scale survey is currently underway to assess the level of Asian giant hornet establishment in both countries and to determine the future direction of eradication efforts.