Effects of Photoperiod and Low Temperature on Larval Development and Freezing-Tolerance of Xestia c-nigrum L. : Lepidoptera : Noctuidae

Larvae of the spotted cutworm, Xestia c-nigrum, were exposed to 5 or 10°C after rearing under long- (16L-8D, 18.5°C) or short-day (10L-14D, 18.5°C) regimes. At such low temperatures, the larvae were able to develop to the advanced instars with feeding activity. The exposure to low temperatures strongly retarded the larval growth but accelerated both freezing-tolerance and accumulation of trehalose. The delay of growth and the increase in freezing-tolerance were conspicuous in the larvae reared under short days before exposure to 5°C : most 5th instar larvae required over 150 days to develop to the next instar and became tolerant to inoculative freezing at -12°C during the first 20 days' exposure. Exposure to 10°C was also effective to increase in freezing-tolerance of the later instar larvae. Short days and low temperatures seem to be important for winter survival of this species.