Effect of sex and age on the supercooling point of the winter-active Diamesa mendotae Muttkowski (Diptera: Chironomidae)

Supercooling points (SCP) of adult Diamesa mendotae Muttkowski, 1915 (Diptera: Chironomidae) were determined at 3, 5, 9, 12 and 17 days post-collection. Supercooling points were recorded using surface contact thermometry and a cooling rate of ca. 1°C min^-1. Female SCPs averaged -22.81, -23.76, -23.85, -23.65, and -20.87°C on each date post-collection and did not differ significantly. Male SCPs were statistically similar and averaged -21.75, -23.53, -23.68, -23.66, and -22.92°C on each date post-collection. Paired comparisons of female/male SCPs on each date post-collection did not show significant differences over time. The overall mean SCP of D. mendotae (-23.05°C) is substantially lower than values of -5.3°C and -5.7°C published for adults and larvae of Belgica antarctica Jacobs 1900 collected at Palmer Station (Antarctica) and -14.2°C for larvae of Paraclunio alaskensis Coquillett 1900 collected at Vancouver Island, British Columbia. In addition, the SCP of this species appears to be lower than that of other winter-active insect species reported in the literature. Although no adults survived after the SCP was recorded, further studies are necessary to determine if D. mendotae is a freeze-intolerant insect. Nevertheless, our results suggest that a low SCP could be used as a mechanism to facilitate emergence and adult activity of this species during winter conditions.