The effect of summer temperature on the distribution of Ceramica pisi (Lepidoptera: Noctuidae) in Iceland

The distribution of Ceramica pisi has been expanding in Iceland after 1990, concurrent with a recent rise in mean annual temperature. A previous study showed that the winter survival of C. pisi is primarily related to pupal mass. We monitored the development of C. pisi larvae over cool, mild, and warm summers in southern Iceland and calculated the total mass-related survival of C. pisi larvae/pupae through pupation and winter. A significant positive relationship was found between a) summer growing degree days and the proportion of larvae that reached critical mass for winter survival, and b) larval mass and likelihood of pupation. We conclude that increased summer temperature is the primary cause of the distribution range shift of C. pisi in Iceland, and this has facilitated increased population density of the species, in combination with increased availability of food resources due to host shift over to Nootka lupin.