Effect of thermal acclimation on the tolerance of the peach fruit fly (Bactrocera zonata: Tephritidae) to heat and cold stress

Abstract

Understanding the thermal biology of insects is of increasing importance for predicting their geographic dis­tribution, particularly in light of current and future global temperature increases. Within the limits set by genetic makeup, thermal tolerance is affected by the physiological conditioning of individuals (e.g., through acclima­tion). Considering this phenotypic plasticity may add to accurately estimating changes to the distribution of insects under a changing climate.
We studied the effect of thermal acclimation on cold and heat tolerance of the peach fruit fly (Bactrocera zonata) – an invasive, polyphagous pest that is currently expanding through Africa and the Middle East. Females and males were acclimated at 20, 25 and 30 ◦ C for up to 19 days following adult emergence. The critical thermal minimum (CT min ) and maximum (CT max ) were subsequently recorded as well adult survival following acute exposure to chilling (0 or − 3 ◦ C for 2 h). Additionally, we determined the survival of pupae subjected for 2 h to temperatures ranging from − 12 ◦ C to 5 ◦ C.
We demonstrate that acclimation at 30 ◦ C resulted in significantly higher CT max and CT min values (higher heat resistance and lower cold resistance, respectively). Additionally, adult recovery following exposure to − 3 ◦ C was significantly reduced following acclimation at 30 ◦ C, and this effect was significantly higher for females. Pupal mortality increased with the decrease in temperature, reaching LT 50 and LT 95 values following exposure to -0.32 ◦ C and − 6.88 ◦ C, respectively. Finally, we found that the survival of pupae subjected to 0 and 2 ◦ C steadily increased with pupal age.
Our findings substantiate a physiological foundation for understanding the current geographic range of B. zonata. We assume that acclimation at 30 ◦ C affected the thermal tolerance of the flies partly through modulating feeding and metabolism. Tolerance to chilling during the pupal stage probably changed according to temperature-sensitive processes occurring during metamorphosis, rendering younger pupae more sensitive to chilling.