Temperature-dependent chemical components accumulation in Hippodamia variegata (Coleoptera: Coccinellidae) during overwintering.

Hippodamia variegata (Goeze) is a widespread predator of aphid and has been reported as the most important naturally occurring enemy of aphids, in many countries. In this study, fluctuating levels of cryoprotectants in nonoverwintering and overwintering coccinellids were assessed in field and natural overwintering sites in Hamadan, Iran, from September of 2010 to June of 2011. Moreover, accumulations of polyols were investigated in response to subzero temperatures. Results demonstrated that concentrations of cryoprotectants changed during the study period under natural conditions. Large amounts of metabolic reserves, in the form of glycogen, accumulated before overwintering. Glycogen began to breakdown but polyols accumulated when ambient temperature decreased from October to December. Overwintering coccinellids displayed a threefold increase in levels of trehalose and a fivefold increase in levels of glucose and total cryoprotectants, but there was even a 45-fold increase in myo-inositol content when subzero temperatures were experienced. It was suggested that myo-inositol and glucose are the major cryoprotectants components in this species. In tests for cold response, the optimal temperature for polyol synthesis seems to be below -3°C. From November to February, all the collected coccinellids that had been kept at 10°C in the laboratory were dead after 30 d, indicating that high temperatures were not favorable for overwintering of this population. Moreover, exposure to high temperatures resulted in rapid catabolism of sugar alcohols. This result demonstrated significant correlation between ambient temperature decrease and accumulation of polyols, suggesting that low temperatures are responsible for polyols synthesis in this species.