Cold hardiness in diapause and non-diapause larvae of the summer fruit tortrix, Adoxophyes orana (Lepidoptera : Tortricidae)

Cold hardiness of larvae of the summer fruit tortrix moth, Adoxophyes orana (Fischer von Rosslerstamm) (Lepidoptera: Tortricidae) was examined in the laboratory. Supercooling point of field collected larvae increased signific antly from a mean value of -23.9 degrees C in February 1998 to -16.9 degree s C in June 1998. Mean supercooling points for laboratory diapause and non- diapause larvae were -20.7 degrees C and -17.2 degrees C respectively. Shor t period of acclimation (10 days at 0 degrees C) significantly decreased su percooling point to -24.7 degrees C for laboratory diapause larvae. Acclima tion for 12 days at 5 degrees C decreased supercooling point to -19.4 degre es C for non-diapause larvae. Pre-freeze mortality for diapause and non-dia pause larvae was also studied. Constant exposure of diapause larvae at -5 d egrees C resulted in high mortality (63.1%) after a period of 30 days. in c ontrast, only 6 days at -5 degrees C were sufficient to cause 100% mortalit y of non-diapause larvae. Mortality of non-diapause larvae reached 100% aft er 12 and 18 days at 0 and 5 degrees C respectively. The importance of thes e findings for the overwintering strategy of A. orana is discussed.