Comparison of cold hardiness and sugar content between diapausing and nondiapausing pupae of the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

To understand overwintering of the cotton boll worm Helicoverpa armigera, cold hardiness and sugar content are compared between diapausing and nondiapausing pupae. Diapausing and nondiapausing pupae reared at 20°C under short and long photoperiods are acclimatized with a reduction of 5°C per 5 days to 0°C. When the acclimation temperature reaches 0°C, the survival of diapausing pupae is assessed. The survival gradually decreases as the period of treatment progresses and approximately half survive for 112 days. However, nondiapausing pupae survive only 14 days after exposure to 0°C. The surpercooling points of nondiapausing, diapausing and acclimatized pupae are approximately -17°C. The major sugars contained in pupae are trehalose and glucose. Even though trehalose contents in diapausing pupae (initial level: 0.6 mg 100 mg^-1 fresh weight) increase significantly during cold acclimation and continue increasing until 58 days after exposure to 0°C (maximum level: 1.8mg 100 mg^-1), glucose is maintained at low levels (0.02 mg 100 mg^-1) for 56 days at 0°C. However, glucose contents increase (maximum level: 0.8 mg 100 mg^-1) with decreasing contents of trehalose 84 days after exposure to 0°C. Glycogen content gradually decreases during cold acclimation. When nondiapausing pupae are acclimatized with a reduction of 5°C per 5 days to 5°C from the beginning of pupation until the eyespots move, trehalose content increases (maximum level: 1.0 mg 100 mg^-1). Glucose contents in nondiapausing pupae increase before eclosion (0.09 mg 100 mg^-1). From these results, diapausing pupae of H. armigera can overwinter in regions where average winter temperatures are higher than 0°C, but nondiapausing pupae cannot.