Expression of heat shock proteins has been proposed as an underlying mechanism of increased cold tolerance in insects exposed to fluctuating thermal regimes (FTRs) in comparison to constant low temperatures (CLTs). We found that the levels of Pahsp70 mRNA increase by up to 3 orders in the linden bugs, Pyrrhocoris apterus exposed to FTR -5 degree C (22h) and 25 degree C (2h). The 2h-long warm pulses, however, were not sufficient for accumulation of PaHSP70 protein and thus no significant difference in expression of PaHSP70 protein was detected between FTR and CLT regimes. Hence, we conclude that the accumulation of PaHSP70 protein is not the mechanism underlying the increased cold tolerance in P. apterus at the particular FTR used in this study. The relevance of some other possible mechanisms is discussed.

Biology Centre ASCR Institute of Entomology and University of South Bohemia Faculty of Science Ceske Budejovice Czech Republic

Physiological basis for low-temperature survival and storage of quiescent larvae of the fruit fly Drosophila melanogaster