Strategies of freeze avoidance in larvae of the goldenrod gall moth, Epiblema scudderiana: Laboratory investigations of temperature cues in the regulation of cold hardiness

Abstract

Laboratory manipulations of ambient temperature were used to investigate the role of temperature in triggering or modulating cold-hardiness adaptations, supercooling-point depression and cryoprotectant accumulation, in larvae of the goldenrod gall moth, Epiblema scudderiana (Clemens), a freeze-intolerant species. Low temperature strongly facilitated cryoprotectant synthesis; larvae subjected to a 1°C per day decrease in temperature showed a major increase in the rate of glycerol synthesis when temperature fell below 5°C with highest rates of synthesis, greater than 90 μmol g −1 d −1, at temperatures between 0 and −10°C. Conversely, abrupt rewarming of larvae from −18 to 23°C in mid-November stimulated a rapid loss of glycerol (from a starting level of 1763 ± 278 μmol/g wet weight) with a half time of only 1.5 days. Supercooling-point depression was not keyed to ambient temperature but appeared to be an endogenous event occurring over the same time interval in laboratory animals held at warm or cold temperatures, as well as in outdoor animals. Rewarming of cold-adapted larvae in November resulted in only a small rise in supercooling point (and did not break diapause) but rewarming in February resulted in a 19°C increase in supercooling point in 4 days, followed rapidly by pupation.