A pioneering pest: the winter moth (Operophtera brumata) is expanding its outbreak range into Low Arctic shrub tundra

Climate warming allows generalist boreal consumers to expand into Arctic ecosystems. We present experimental and observational field data showing that a generalist boreal insect pest the winter moth (Operophtera brumata Linnaeus, 1758) is expanding its outbreak range out of the northern boreal mountain birch forest in northeast Fennoscandia and into the adjacent Low Arctic shrub tundra. This is the first documented example of an outbreaking boreal insect pest expanding into a tundra ecosystem. The expansion has coincided with a long-term advancing trend in the expected hatching date of moth eggs in spring for the study region. We show that the winter moth can complete development on Low Arctic willows and that the density of winter moth larvae in willow thickets is unrelated to the amount of mountain birch (the main host plant in northern boreal forest) in the thickets. However, we also demonstrate that larval densities on willows show a regional-scale spatial decline when moving away from the birch forest and into the shrub tundra. Continued monitoring is needed to establish whether the outbreaks will spread farther into the tundra. The expansion of outbreaking boreal pests into the tundra could alter conventional expectations of increasing vegetation productivity and shrubification in tundra ecosystems.

Automated summary

Climate warming enables generalist boreal consumers to extend their range into Arctic ecosystems. Experimental and observational data show that the winter moth, a generalist boreal insect pest, is expanding its outbreak range from the northern boreal birch forest into the Low Arctic shrub tundra. This expansion is accompanied by an advancing trend in the hatching date of moth eggs. The winter moth can develop on Low Arctic willows, and the larval densities decline regionally when moving from the birch forest to the shrub tundra.