Effects of Temperature on Developmental Rate, Distribution, and Establishment of Calophasia lunula (Lepidoptera: Noctuidae), a Biocontrol Agent for Toadflax (Linaria spp)

A degree-day model was developed for preimaginal development and oviposition of Calophasia lunula (Lepidoptera: Noctuidae), a European moth which has been introduced into North America for biological control of toadflax (Linaria spp.). Its developmental rate fits well to a linear model with a threshold of 13.5 degrees C, 418 degree-days required for preimaginal development, and an additional 124 degree-days for 95% oviposition. Parameters for two strains originating from Switzerland and the former Yugoslavia are very similar, but the Yugoslav strain has a slightly higher degree-day requirement. The model predicts that two or more generations will occur in southern Europe, that one generation will occur in central Europe, and that the insect will be absent from northern Europe. Most locality records for C. lunula in Europe fall within the predicted distribution. However, the insect extends further north in Scandinavia than predicted by the model, suggesting that a strain adapted to a lower summer temperature may occur there. In North America it has become established only in areas predicted by the model to be within its range. According to the model, central and northern Alberta, where extensive unsuccessful releases have been made, are outside its potential range. Establishment may be possible in southern British Columbia, southeastern Alberta, and southern Saskatchewan.