Effects of Thermal Acclimation on the Tolerance of Bactrocera zonata (Diptera: Tephritidae) to Hydric Stress

Insects, similarly to other small terrestrial invertebrates, are particularly susceptible to climatic stress. Physiological adjustments to cope with the environment (i.e., acclimation) together with genetic makeup eventually determine the tolerance of a species to climatic extremes, and constrain its distribution. Temperature and desiccation resistance in insects are both conditioned by acclimation and may be interconnected, particularly for species inhabiting xeric environments. We determined the effect of temperature acclimation on desiccation resistance of the peach fruit fly (Bactrocera zonata, Tephritidae) - an invasive, polyphagous pest, currently spreading through both xeric and mesic environments in Africa and the Eurasian continent. Following acclimation at three constant temperatures (20, 25, and 30 degrees C), the survival of adult flies deprived of food and water was monitored in extreme dry and humid conditions (90% relative humidity, respectively). We found that flies acclimated at higher temperatures were significantly heavier, and contained more lipids and protein. Acclimation temperature significantly and similarly affected the survival of males and females at both high and low humidity conditions. In both cases, flies maintained at 30 degrees C survived longer compared to 20 and 25 degrees C - habituated counterparts. Regardless of the effect of acclimation temperature on survival, overall life expectancy was significantly shortened when flies were assayed under desiccating conditions. Additionally, our experiments indicate no significant difference in survival patterns between males and females, and that acclimation temperature had similar effects after both short (5-10 days) and long (11-20 days) acclimation periods. We conclude that acclimation at 30 degrees C prolongs the survival of B. zonata, regardless of ambient humidity levels. Temperature probably affected survival through modulating feeding and metabolism, allowing for accumulation of larger energetic reserves, which in turn, promoted a greater ability to resist starvation, and possibly desiccation as well. Our study set the grounds for understanding the phenotypic plasticity of B. zonata from the hydric perspective, and for further evaluating the invasion potential of this pest.