اندازه گیری تحمل به سرما با شیوه سنجش پویا در دو جمعیت دروزوفیلای بال خالدار (Drosophila suzukii)

Drosophila suzukii Matsumura (Diptera, Drosophilidae) is a polyphagous pest with a worldwide distribution. However, the only record from the Middle East is an accidentally capture of D. suzukii at olive orchards of Qazvin, Iran. The range expansion of D. suzukii is directly related to its climate requirements and limitations. There are two different approaches to assess thermal tolerance in insects: 1) static tolerance assays, in which insects are exposed to acute stressful temperatures, and 2) dynamic (ramping) tolerance assays, which tests insects for a natural increase/decrease in temperature. Ramping thermal assay is more ecologically relevant than static assay as it would better portray the thermal tolerance of insects in field. The present study examined the cold tolerance of two populations (Colorado and Hawaii) of D. suzukii using ramping assay, in which supercooling point (SCP) and lower lethal temperature for 50% mortality (Lower LTe50) were measured. To measure SCP, 3-day-old adults were individually (replicated 25 times) attached to a type-K copper-constantan thermocouple, which was interfaced to a computer through a TC-08 temperature and voltage data logger and PicoLog Beta 6.1.12-beta.2 software. The adults were then placed in holes of an aluminum block, which were immediately placed within a programmable freezer equipped with a 1/4 DIN microprocessor-based ramping temperature control. The insect temperature was ramped down at 1 °C min-1 from 20 to -30 °C, and SCP was determined as the lowest temperature just before exothermic reaction. To measure Lower LTe50, the same procedure was used but adults were tested in groups of 10 (replicated 8 times for each of 8 target temperatures between 0 and -20 °C) in 1-ml Eppendorf tubes inside which the thermocouples were attached. The insect temperature was ramped down at 0.1 °C min-1 from 20 °C to the target temperature. The insect were then exposed to room temperature, and mortality was recorded after 24 h. There was a significant difference between mean SCP of Colorado (-20.4 °C) and Hawaii (-22.2 °C) populations. Also, a significant difference between mean Lower LTe50 of Colorado (-8.8 °C) and Hawaii (-7.3 °C) populations was observed. These findings show that Lower LTe50 is more ecologically relevant for D. suzukii populations, but SCP may be related to a different set of physiological adaptations.