A native insect on a non-native plant

The trans-Palearctic moth Phyllonorycter populifoliella (Lepidoptera: Gracillariidae) is a major pest of the North American Populus balsamifera and its hybrids widely planted as ornamentals in North Asia (i.e., the Asian part of Russia). We DNA barcoded Ph. populifoliella from distant geographical populations in Russia and analyzed them together with the data from eight European countries and India to estimate intraspecific variability and the haplotype richness in the Palearctic, and specifically in North Asia. Furthermore, using next-generation sequencing (NGS, Sequel platform, PacBio), we investigated larval and pupal remnants found in an old herbarium from the Nearctic, where P. balsamifera occurs naturally, to verify if any events of the moth introduction to this biogeographic zone happened in the past. Relatively high intraspecific variability in the COI gene of mtDNA, reaching 3.73%, was recorded in Ph. populifoliella. Overall, 30 COI haplotypes were defined in 83 specimens from the Palearctic, with a noticeable richness in North Asia (21 haplotypes). Using NGS, the remnants of 14 Phyllonorycter specimens dissected from up to 174-year-old herbaria from the Palearctic and Nearctic were sequenced, and four moth species were identified. Among them, there were three Palearctic species, Ph. populifoliella, Ph. pastorella (Zeller), and Ph. apparella (Herrich-Schäffer), and one Nearctic, Ph. nipigon (Freeman). No evidence of Ph. populifoliella introduction to North America was documented based on the examination of the herbarium dated 1850–1974. Three specimens of Ph. populifoliella identified from herbaria from Austria and Poland (dated 1879–1931) represented one haplotype (H7) known from the recent time. Overall, our study clarifies the modern range, provides insights into phylogeography, and defines the haplotype richness of the native leafminer outbreaking on the alien host. Furthermore, it underlines the use of old herbaria to explore the historical distribution of endophagous insect species.