Importance of the Body Water Management for Winter Cold Survival of the European Corn Borer Ostrinia Nubilalis Hübn. (Lepidoptera: Pyralidae)

Abstract

ABSTRACTWinter diapause, a common strategy of many insect species occupying temperate regions, is usually closely related to and coincides with their cold hardiness. Freezing of body fluids represents one of the major obstacles for sub-zero temperatures survival and thus the body water management is an important part of cold hardiness. In this study, we examined some cryobiological parameters, as well as content of glycerol and trehalose in non-diapausing and freeze tolerant diapausing larvae of the European corn borer, Ostrinia nubilalis. Diapausing larvae were divided into two experimental groups—a group exposed to field temperatures (which were in average above 0°C) and a group exposed to -8°C for ten days. Contents of the total body water, osmotically active (OA) and inactive (OI), as well as the supercooling point (SCP) of hemolymph and fat body, were measured by differential scanning calorimetry (DSC). The content of glycerol and trehalose was analysed by gas chromatography. Compared to diapausing groups, non -diapausing larvae had higher SCP, lower content of trehalose and glycerol in both tissues. The content of total and OA water in both tissues of diapausing larvae had changed with low temperatures exposure. At -8°C, the amount of total and OA body water was decreased in hemolymph and increased in fat body while the content of OI water was slightly increased in hemolymph but remained unchanged in fat body. Mean SCPs of both tissues were significantly different—for hemolymph it was around -21°C, which was almost two times lower than for fat body (-10°C). However, the SCPs of fat body and hemolymph had not significantly changed after the exposure to low temperature. The content of glycerol and trehalose was far greater in hemolymph than in fat body for all groups, which is in accordance with the difference between the SCPs of these tissues. Furthermore, exposure of diapausing larvae to sub-zero temperatures (-8°C) had simultaneously provoked an increase in glycerol/trehalose concentration in hemolymph and the decrease in fat body. These adjustments of water and cryoprotectors distribution are an important part of cold hardiness mechanisms.