Northerly shift in voltinism watershed in Hyphantria cunea (Drury) (Lepidoptera: Arctiidae) along the Japan Sea coast: Evidence of global warming?

Abstract

The effects of climate change on the northern limit of the trivoltine area were clarified in the fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Arctiidae). The Takaoka and Kanazawa populations used in the present study occur in locations to the north of Fukui (36.07°N), where H. cunea has recently shifted from a bivoltine to a predominantly trivoltine life cycle. The life-history traits of these populations were investigated and compared to those in the Fukui population. The lower threshold temperature for development and the thermal constant for one generation were 11.3°C and 674.5°d in the Takaoka population, and 11.2°C and 680.7°d in the Kanazawa population. The critical photoperiod for diapause induction at 25°C was 14 h 34 min in the Takaoka population and 14 h 28 min in the Kanazawa population. These critical photoperiods at 25°C were longer by 24 min and 18 min than the Fukui population, respectively. These results, together with climate data, suggest that the Takaoka population maintains a bivoltine life cycle, and a small part of the Kanazawa population has three generations per year, a predominantly bivoltine life cycle. Thus, the present northern limit of the trivoltine area lies around Fukui in districts along the Japan Sea.