Thermal stress induces HSP70 proteins synthesis in larvae of the cold stream non-biting midge Diamesa cinerella Meigen.

Laboratory experiments on the cold stenothermal midge Diamesa cinerella (Diptera, Chironomidae) were performed to study the relationship between temperature and heat shock proteins (HSP70) expression at translational level (Western blotting). Thermotolerance of IV instar larvae collected in nature at 1.5-4.3 °C were analyzed through short-term (1 h at ten different temperatures from 26 °C and 35°C) and long-term (2-14 h at 26°C and 2-4 h at 32°C) heat shocks. A high thermotolerance was detected (LT50 = 30.9-32.8 °C and LT100 =34.0-37.8 °C). However, survival decreased consistently with increasing exposure time, especially at higher temperature (LTime50 = 7.64 h at 26°C and LTime50 = 1.73 h at 32°C). The relationship between such heat resistance and HSP70 expression appeared evident since a relationship between HSP70 level and survival rate was generally found. A Heat Shock Response was consistent only in the summer larvae, but the highest levels of HSP70 both in the control and in heat stressed larvae were found in the winter population. The high resistance to heat found in the winter population (LT50= 32.5 ± 0.5 °C) seems to be given more by constitutive high levels of HSP70 proteins than by HSR induction. Altogether these results stressed how the HSP70 protein family confers resistance against cold, being detected under natural conditions in control larvae collected in all seasons, and against heat under shocks. These results give new insights into possible responses to climate changes in freshwater insects within the context of global warming.