<p>The effects of climate change on life-history traits and the boundary between bivoltine and trivoltine areas in the northern Kanto district were investigated in 5 populations of the fall webworm <i>Hyphantria cunea</i> (Drury) (Lepidoptera: Arctiidae), inhabiting from 36.1 ºN to 36.6 ºN in the mid-2010s. Photoperiodic responses controlling diapause induction were investigated at 25ºC and developmental traits were examined at 5 temperatures between 18 and 25ºC. The photoperiodic responses of Utsunomiya, Tsukuba, and Maebashi populations were compared with those investigated in the early 1990s. The critical photoperiods were the longest in the Utsunomiya population and the shortest in the Maebashi population among all of those studied, and these were nearly the same as those of the early 1990s. The critical photoperiod of the Tsukuba population had been shortened by 11&#xa0;min from that of 1993, indicating that the life cycle of this population had shifted from mixed to trivoltine. The Mito population showed a critical photoperiod near that of the Utsunomiya population, and the Ashikaga population had a value very similar to that of the Tsukuba population obtained in 1993. Life cycles of all populations were estimated from the life history traits and climate data at each site. The estimations suggested that trivoltine life cycles would prevail in Ashikaga, Tsukuba, and Maebashi populations and others would be bivoltine although the Ashikaga population may show a mixed life cycle.</p>