Lower lethal temperature for adult maleDiamesa mendotaeMuttkowski (Diptera: Chironomidae), a winter-emerging aquatic insect

The supercooling point (SCP) and lower lethal temperature (LLT50) of male adult Diamesa mendotae Muttkowski (Diptera: Chironomidae) were determined from field-collected individuals. SCP determined using surface-contact thermometry did not differ statistically from previously reported values for a previous generation of this species. The LLT50 was determined by exposing individuals to −10, −15, −20, −25, and −30°C for one minute. Mean survivorship was 96.7, 91.2, and 71.2% for tests at −10, −15, and −20°C, respectively. Exposure to −25 and −30°C resulted in 100% mortality in all tests. Results show that males of D. mendotae are freeze-intolerant with a mean SCP of −21.6°C which is only 0.1°C lower than its linear interpolated estimated LLT50 of −21.5°C. Our results confirm that a low SCP, rather than freeze tolerance, is a mechanism that facilitates emergence and adult activity of this species during winter conditions. The implications of SCP and LLT50 with regard to life cycle dynamics are discussed.