On the Question of Parameters for Evaluating Cold Hardiness of Freeze Tolerant Insects

The super cooling point (SCP) is the best documented parameter for describing the ability of insects to survive freezing but its value as a predictor of overwintering survival or for estimation of the cold hardiness potential, is limited. According to this study, the SCP is influenced by such factors as polyol and protein concentration in the hemolymph; therefore it can be lower in winter than it is in spring. Nevertheless the quality of ice nucleating process is higher in winter insects due to which insects survive the lowest winter temperatures. The depletion of polyols in spring causes increase of SCP. Unlike in the autumn, when an increase in SCP is associated with development of freeze tolerance, spring changes in SCP of the insects occur simultaneously with loss of cold tolerance. The present study on the freezetolerant Upis ceramboides inhabiting central Yakutia (Eastern Siberia, Russia) shows that SCP itself is not a sufficiently appropriate parameter for evaluation of insect cold hardiness. For these purposes it should be used together with other criteria, such as specific ice nucleating activity and profile of ice nucleating activity. Obviously, ice nucleation at this temperature was non-specific and therefore likely had no adaptive importance. The data testifies that the SCP does not reflect the real process associated with cold hardiness in the overwintering insects. Moreover, developing researches associated with different aspects of insect`s cold hardiness leads to understanding that “SCP is no longer deemed an adequate predictor of overwintering survival for many species” [15]. It is also limited in estimating of the cold hardiness potential [11]. In this study, freeze tolerant beetles Upis ceramboides inhabiting central Yakutia (Eastern Siberia) were used to investigate how seasonal changes in the physical and chemical situation in the insect hemolymph influence their SCP to better understand the role of SCP in estimating of insect cold hardiness. Materials and Methods Insects A large (up to 340 mg) tenebrionid beetles, U. ceramboides (Coleoptera: Tenebrionidae) were collected under loose bark of dead standing birch in the vicinity forest of Yakutsk city. Beetles to be used in the experiments were collected in 20th December, 2nd March, 4th April and 10th July. In its habitat of overwintering that is situated above snow line, the beetles can be exposed to winter temperatures as low as -55°C. The beetles collected in winter and early spring were kept at +4°C until they started to move. Summer specimens were placed at +4°C for 4 hours before experiments get started. This procedure was necessary for evacuating of ice nucleating agents from the gut. Citation: Li N (2014) On the Question of Parameters for Evaluating Cold Hardiness of Freeze Tolerant Insects. Entomol Ornithol Herpetol 3: 127. doi:10.4172/2161-0983.1000127