Abstract
Strong tolerance of freezing is an important strategy for insects living in extremely cold regions. They produce highly effective cryoprotectant systems consisting of ice-nucleating proteins and polyols, which enables tolerable freezing of the body fluid. Therefore, the measurement of the concentrations of polyols and the activity of ice nucleators in the haemolymph is an essential tool for describing tolerance to ice formation in insects occurring in particularly cold places. This study evaluates three parameters: insect body supercooling point (SCP), haemolymph glycerol content and the profile of haemolymph ice nucleating activity that characterize the strategies of cold adaptation and cold hardiness in two previously unstudied beetles, Chrysolina graminis graminis L. and Galerucella nymphaea L., inhabiting Yakutia (Russian Far East, latitude 62°N). The high SCP values, ice nucleating activity and survival of the chrysomelids after freezing indicate that both species are tolerant of freezing. According to the profiles of ice-nucleating activity, the haemolymph from C. graminis graminis is characterized by a higher nucleating potential than that from G. nymphaea. The glycerol level is also higher in C. graminis graminis. The results indicate that both species develop tolerance to low temperatures, but the cold hardiness potential of C. graminis graminis is greater than that of G. nymphaea. This was revealed by the survival test, in which beetles were frozen to a temperature of -22°C for 30 min; 86% of C. graminis graminis and 72% of G. nymphaea survived the test. Thus, the freeze-tolerance of these beetles seems to be based on the production of an integrated cryoprotectant system, the quality of which apparently influences the range of their cold resistance.
Highlights
Insects inhabiting extremely cold regions are mainly able to survive the harsh climatic conditions there by being tolerant of freezing, which makes them different from insects inhabiting areas with mild climates, which have evolved mechanisms that enable them to avoid freezing (Miller, 1985; Duman et al, 1991; Sinclair et al, 2003; Zachariassen & Kristiansen, 2003; Lee, 2010)
Studies on Siberian insects, such as Aporia crataegi L. (Lepidoptera: Pieridae) and others, have demonstrated that their cold hardiness potential is associated with the production of an effective cryoprotectant system consisting of polyols and ice-nucleating proteins (INPs) (Li, 2011, 2012)
The aim of this study is to determine, using the approach described, the type of cold adaptation strategy and cold hardiness potential of two yet unstudied species belonging to the family Chrysomelidae (Coleoptera), Chrysolina graminis graminis L. and Galerucella nymphaeae L., inhabiting central Yakutia
Summary
Insects inhabiting extremely cold regions are mainly able to survive the harsh climatic conditions there by being tolerant of freezing, which makes them different from insects inhabiting areas with mild climates, which have evolved mechanisms that enable them to avoid freezing (Miller, 1985; Duman et al, 1991; Sinclair et al, 2003; Zachariassen & Kristiansen, 2003; Lee, 2010). Like the INPs in Tipula trivittata (Yeng et al, 1991), those in Siberian insects apparently have the ability to aggregate, forming a template around which an ice crystal can form and grow to become large enough to ensure freezing at subzero temperatures (Li, 2012). In this way it is likely that ice nucleating agents initiate safe and controlled ice formation in the extracellular environment at subzero temperatures before ice can form inside cells, which is fatal for many insects (Zachariassen, 1985)
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