Slow-range-expansion
Guides
Depressaria radiella
parsnip moth, parsnip webworm
Depressaria radiella is a Eurasian moth introduced to North America in 1862 (Ontario) and New Zealand in 2004. It is a 'superspecialist' herbivore effectively restricted to two closely related apiaceous genera (Heracleum and Pastinaca) throughout its native and introduced ranges. The species is univoltine, with adults active from August through May after overwintering. It has undergone slow westward expansion across North America over 160+ years, reaching the West Coast only after more than 50 years. The species exhibits lower genetic diversity than its congener D. depressana, possibly reflecting its narrow host specialization.