Entering diapause is a prerequisite for successful cold-acclimation in adult Graphosoma lineatum (Heteroptera: Pentatomidae).

In diapause adults of Graphosoma lineatum overwintering in a field-cage, high chill-tolerance (CT) developed gradually, within 5 months from August to December. In laboratory-acclimation experiments, the diapause state appeared to be an essential pre-condition for successful cold-acclimation and overwintering. First, diapause prevented elevation of the median supercooling point (SCP) by about 5.5 degrees C that accompanies the onset of reproductive activity in non-diapause specimens. Second, diapause allowed subsequent physiological changes resulting in cold-acclimation during a gradual (18-day) decrease of temperature from 25 to 0 degrees C. No, or very modest, cold-acclimation was observed in non-diapause specimens. Decrease of temperature led to a rapid loss of ca. 1/3 of the body water in both non-diapause and diapause specimens. Approximately 0.1 M of trehalose accumulated in tissues of diapause specimens only, and haemolymph osmolality rose from 347 mOsm (at 25 degrees C) to 444 mOsm after an 18-day cold-acclimation and to 764 mOsm during further storage at 0 degrees C for 100 days. Upon transfer of cold-acclimated diapause specimens back to 25 degrees C for one week (de-acclimation), the high CT was lost, the SCP elevated by about 2.5-3 degrees C, and the levels of trehalose, water content and haemolymph osmolality returned to pre-acclimation or non-diapause levels.

Cryoprotective role of polyols independent of the increase in supercooling capacity in diapausing adults of Pyrrhocoris apterus (Heteroptera: Insecta).

Diapausing cold-acclimated adults of the bug Pyrrhocoris apterus accumulate four 'winter' polyols, ribitol, sorbitol, mannitol and arabinitol, in total concentrations of up to 100 mM. The accumulation started only when the temperatures dropped below a threshold of +5 degrees C in laboratory acclimated insects. The supercooling capacity (SCP) was not affected by polyol accumulation and remained constant at approximately -17 degrees C. Cold hardiness, measured as survival time (Lt50) at -15 degrees C, increased from approximately 1 day to approximately 1 week in parallel with polyol accumulation. There was a tight correlation (r=0.98) between the concentration of 'winter' polyols in haemolymph and Lt50(-15). When a mixture of ribitol and sorbitol was injected into the haemolymph of the bugs acclimated to +5 degrees C, the concentration of polyols increased from 2.5 to 83.1 mM in haemolymph, or from 0.07 to 6.61 microg/mg of fresh weight in the whole body, the SCP remained unchanged and survival after exposure to -14 degrees C for 3 days increased approximately three-fold in comparison to untreated controls. Such results were interpreted as evidence for the cryoprotective role of accumulated polyols independent of the depression of SCP. Acclimation protocol using thermoperiod, mimicking daily temperature oscillations, resulted in moderately lower SCP, higher sum of polyols accumulated and significantly longer Lt50(-15) than at acclimation protocol with constant temperatures.