Genetic Structure and Colonization of North America by Depressaria depressana (Fabricius 1775) (Lepidoptera: Depressariidae) over 15 Years; Contrasts with Westward Expansion of Depressaria radiella (Goeze, 1783) over 160 Years

SIMPLE SUMMARY: As invasive insect species can disrupt agriculture, ecosystem functions, and human health, monitoring the spread of newly invasive insects is a high priority. The purple carrot-seed moth Depressaria depressana, a European species first reported in North America in 2008, specializes on reproductive structures of taxa throughout the family Apiaceae and thus presents a potential threat to native North American umbellifers. We assessed interpopulational genetic diversity of D. depressana across its eastern North American invasion front and compared those values to available data for European populations. We also compared this diversity with genetic diversity estimates for populations of Depressaria radiella (parsnip webworm), a European species introduced to North America more than 160 years ago that is essentially restricted to two apiaceous genera throughout its native and invasive ranges. Documenting the historical spread of D. radiella with museum and literature records, we found D. depressana displays greater genetic diversity than D. radiella and is colonizing North America more rapidly; greater genetic diversity may facilitate faster colonization via establishment on a wider range of hostplants. The contrast in colonization by these two species may inform management practices for invasive insects utilizing a broad versus narrow array of hosts within a single plant family. ABSTRACT: Depressaria depressana, the purple carrot seed moth, is a Eurasian species first reported in North America in 2008 and currently undergoing range expansion. This invasion follows that of its Eurasion congener Depressaria radiella (parsnip webworm), first documented in North America 160 years ago. Unlike D. depressana, which utilizes hostplants across multiple tribes of Apiaceae, Depressaria radiella is a “superspecialist” effectively restricted in its native and non-indigenous ranges to two closely related apiaceous genera. We investigated the genetic structure of D. depressana populations across latitudinal and longitudinal gradients in the eastern United States by constructing COI haplotype networks and then comparing these with haplotype networks constructed from available COI sequence data from contemporary European D. depressana populations and from European and North American D. radiella populations. Haplotype data revealed higher genetic diversity in D. depressana, indicating high dispersal capacity, multiple introductions, and/or a genetically diverse founding population. Museum and literature records of D. radiella date back to 1862 and indicate that range expansion to the West Coast required more than 50 years. Higher levels of genetic diversity observed in D. depressana compared to its congener may indicate a greater propensity for dispersal, colonization and establishment in its non-indigenous range.