INFLUENCE OF TEMPERATURE, DURATION OF CONDITIONING, AND AGE OF ANAGASTA (EPHESTIA) KÜHNIELLA (ZELL.) (LEPIDOPTERA:PYRALIDIDAE) ON ACCLIMATION TO A SUB-ZERO TEMPERATURE

Abstract

When Anagasta (Ephestia) kühniella pupae of age groups 0.5, 1.5, 2.5, 3.5, and 4.5 days were conditioned at 5°, 10°, 15°, 20°, and 25 °C for 1, 2, 4, 8, and 16 hours, the mortality due to subsequent exposure at −15 °C for 4 hours was affected by each of the three factors, age, temperature, and duration of conditioning. As the temperature of conditioning was lowered from 25° to 10 °C, the mortality due to the sub-zero exposure gradually decreased; when conditioned at 5 °C mortality increased again. When conditioned for 1–16 hours the lowest average mortality was among the pupae conditioned for 4 hours; mortality was highest for 1 and 16 hours. Regardless of the temperature and duration of conditioning, pupal mortality due to sub-zero exposure increased as the age increased.Pupae conditioned at 10 °C, when deacclimated at 25 °C for 2–8 hours, exhibited a gradual increase in mortality, showing a tendency to reach the same high level as among the unacclimated.Adults 1.5, 2.5, 3.5, 4.5, 5.5, and 6.5 days old, when exposed to −15 °C for various durations, exhibited only a slight difference in the time required to kill 50% (ET₅₀) in each of the age groups; the two oldest groups required the shortest exposures, between 50 and 60 minutes. Moths of a given age group, when conditioned at 10 °C, exhibited higher mortality after sub-zero exposure than the controls; hence, there was no acclimation. Without a subsequent sub-zero exposure, conditioning at 10 °C had no lethal effect on the insects.