Lower lethal temperature for adult male Diamesa mendotae Muttkowski (Diptera: Chironomidae), a winter-emerging aquatic insect

The supercooling point (SCP) and lower lethal temperature (LLT ₅₀) 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.