Environment and Natural Resources, University of Iceland, Sturlugata 7, 101 Reykjavík, Iceland
Nootka lupine (Lupinus nootkatensis) was introduced from Alaska (USA) to Iceland in 1945, becoming naturalized in the 1950s. Currently, this invasive plant occurs throughout Iceland and continues to spread, creating monocultures that change soil conditions and species diversity. Three Icelandic moths – the red-backed cutworm (Euxoa ochrogaster), broom moth (Melanchra pisi), and satyr pug (Eupithecia satyrata) – have shown host expansion to Nootka lupine. These moths are generalist herbivores, and both the broom moth and satyr pug can cause damage to various tree species, while the red-backed cutworm can be a horticultural pest. Data gaps exist on the interactions of these moths with alien and native plants in Iceland. In 2015, I began to assess the distribution and herbivory in southern Iceland of the red-backed cutworm, and subsequently that of the broom moth and satyr pug, on Nootka lupine (alien invasive plant, n=6 sites), and compared them to areas with lyme grass (Leymus arenarius, native plant, n=6 sites) and neighbouring horticultural crops (alien plants, n=6 sites). Larval surveys were conducted in late May-June (red-backed cutworm) and August (broom moth and satyr pug) by checking individual plants for herbivory and larvae for 20 minutes. Moreover, a 50 m transect line with randomly placed 0.25 m2 quadrats were used to further assess plant cover and larval abundance of the red-backed cutworm. Adult surveys occurred in August for the red-backed cutworm using pheromone traps which attract male adults. Results indicate that between 2015–2017, the larval abundance of red-backed cutworms ranged from 0-31 larvae/site. Sites with Nootka lupine had the highest larval abundance, but it was not significantly greater than in sites with lyme grass. The abundance of male adults of red-backed cutworm varied greatly among years regardless of host plant. Overall, 65 males/site were found in 2015, whereas in 2016 and 2017 less than 1 male/site. Red-backed cutworm herbivory on alien plants included Nootka lupine, rutabagas (Brassica napobrassica), and carrots (Daucus carota). Herbivory also occurred on five native plants including lyme grass. Broom moth herbivory occurred on alien plants such as Nootka lupine, rutabagas, rapeseed (B. napus), carrots, and on at least seven native plants. This study highlights the importance of long-term monitoring to assess herbivory dynamics of native insects and their interactions with alien and native host plants, including agricultural systems.