Seasonal trends in acclimatization to cold in the Queensland fruit fly (Dacus tryoni, Diptera) and their prediction by means of a physiological model fed with climatological data.

This paper demonstrates the predictability and significance of changes in the temperature threshold for cold-torpor and in the threshold for survival at sub-zero temperatures in two contrasting types of climate. Both thresholds alter on a seasonal basis in both types of climate and it is observed that temperatures prevailing in autumn cause acclimatization for winter long before winter arrives.Torpor thresholds can be accurately predicted in laboratory-simulated climates by use of a model. When the model is used for field predictions, using shade temperature data from the field, it is only successful in predicting accurate threshold values for those parts of the year during which there is a downward trend in threshold.The relative importance of torpor-avoidance and frost-resistance is discussed with reference to records of the frequency and extent of various degrees of cold in the field. It is concluded that the marked lowering of torpor threshold prior to winter is of great significance in enabling overwintering flies to stay in their sheltered hibernacula. The relatively slight lowering of temperature threshold for frost-survival is only of significance in certain climates. It greatly improves chances of forst-survival in climates where yearly minima fall predominantly in the range-2.65°C to-4.05°C. Acclimation is not necessary for frost survival in climates where the yearly minima stay above-2.65°C whereas acclimation is ineffective in preventing frostinduced extinction when yearly minima fall below-4.5°C.