Multiple component system of sugars and polyols in the overwintering spruce bark beetle, Ips typographus

Overwintering adults of the spruce bark beetle, Ips typographus (L.) showed an unusually complex sugar/polyol cryoprotectant system. The major components of the multiple system were: glucose (177.6 mmol L−1, March); trehalose (175.0 mmol L−1, December); sorbitol (147.9 mmol L−1, January); mannitol (81.2 mmol L−1, March); and erythritol (40.7 mmol L−1, March) (in the parentheses, the maximum concentrations are shown and the month when they were reached). Other minor components were glycerol, fructose, threitol, myo-inositol, arabinitol and ribitol. Distinct seasonal patterns of accumulation/depletion in various components were found. Glycerol, trehalose and glucose started to accumulate first, during early autumn, when the air temperatures fluctuated between 20 and 0 °C, and diapause beetles continued in feeding. Glycerol was depleted, glucose remained stable and trehalose continued in accumulation during late autumn when the temperatures oscillated around 0 °C. During early winter severe frosts reaching −20 °C came, the beetles terminated their diapause and trehalose was partially depleted, while mannitol, sorbitol, fructose, threitol and erythritol started to accumulate. Cold weather continued also during late winter when the beetles remained quiescent. During this period, trehalose was re-accumulated, threitol and erythritol continued to increase, mannitol remained stable and sorbitol, fructose decreased. All cryoprotectans were finally cleared in the beetles which were spontaneously leaving bark during early spring. The seasonal maximum of total concentration of all cryoprotectants (578.2 mOsmol L−1) was reached in March. Such a concentration results in colligative depression of melting point of body fluids down by 1.08 °C only. It suggests that the potential cryoprotective effect of accumulated sugars and polyols was related rather to their non-colligative functions.