INCREASE IN COLD-SHOCK TOLERANCE BY SELECTION OF COLD RESISTANT LINES IN DROSOPHILA-MELANOGASTER

1. In Drosophila melanogaster, the cold-shock tolerance of adult flies at -7-degrees-C increased 22% after a prior 2 h exposure to 4-degrees-C as measured by LD50, the dose (degree minutes of exposure to subzero temperature) which resulted in 50% mortality. 2. Cold-shock tolerance was further significantly increased by selecting cold resistant lines by exposure of adults (1) to 4-degrees-C for 2 h (short-term chilling), or (2) to -7-degrees-C for 80-120 min (cold shock), or (3) to short-term chilling followed by cold-shock. 3. After ten generations of selection, the greatest increase in cold-shock tolerance was found in flies selected using the combined exposure of short-term chilling and cold shock. LD50s increased 33% in comparison with the unselected control strain when no chilling pre-treatment was given prior to cold shock at -7-degrees-C. 4. The rapid cold-hardening response increased 82% in the line selected by the short-term chilling and cold-shock regime. 5. The enhanced cold-shock tolerance was relatively stable since no decrease was observed after four generations without selection. 6. This report shows the role of short-term adaptation as well as selection in the capacity to survive low temperatures in non-diapausing stages of insects.