Acclimation of different strains of the olive fly, Dacus oleae, to low temperatures

Male and female D. oleae have similar powers of acclimation when exposed to low temperatures. Their torpor thresholds depend upon the temperature to which they have been acclimatised. During slow cooling (i.e. less than 1°C per min) they are capable of some rapid acclimation which enables them to lower their torpor threshold by almost 1°C degree, as compared with when they are chilled quickly. After abrupt transfer from 25°C to a different temperature, acclimation takes some time to be accomplished. At 15°C and above it occurs within 10 days but at temperatures below this, progressive acclimation lowers the torpor thresholds to the very low levels typical of flies overwintering under natural conditions. During this long term acclimation torpor thresholds may change by almost 0.5°C per 1°C change of acclimation temperature.No differences were observed in the ability of either flies from northern and southern Greece, or normal and γ-irradiated laboratory reared flies to acclimate to winter conditions in the field. In all cases, torpor thresholds were progressively lowered in advance of the decline in weekly minimum temperatures.