SFORMO TODD, TS: Minimum Flight Temperature and Thermoregulatory Performance of Sub-arctic Dragonflies

Sub-arctic dragonflies (Odonata: Anisoptera), an order of insect previously not studied in Alaska, provide a unique system with which to examine questions of thermal biology. Two potential adaptations are the ability to initiate flight at low temperature and to thermoregulate. To establish minimum flight temperatures, I record the lowest temperature at which a species can maintain level flight, both in the lab and in the field. To determine thermoregulating ability, I measure thoracic temperature (Tth) of individual dragonflies using a thermocouple. Tth is then compared to the dragonfly model providing the operative environmental temperature (Te). By regressing Tth on Te, the slope of the regression line indicates thermoregulatory ability (Thermoregulation Performance Index). I predict that northern dragonflies will have lower minimum flight temperatures than comparable species from lower latitudes. I also predict a general pattern wherein more massive species are able to thermoregulate by both physiological and behavioral means, while less massive species rely solely on behavioral repositioning. The relationship between Tth of living specimens and Te is examined for each species and compared across species to examine relative thermoregulating ability. I show, contrary to speculation by Vogt and Heinrich (1983), that minimum flight temperature of northern dragonflies are not different from comparable species from Maine, although they differ from species in Florida. Minimum temperatures range from 14�C for S. danae to 22�C for aeshnids. Finally, I conclude that the relative thermoregulating ability is a function of mass, which ranges from 0.09g for the least to 0.86g for the most massive, while the Thermoregulatory Performance Index ranges from 0.90 (a thermal conformer) to 0.14 (a thermal regulator), respectively.