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

Abstract

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.