Cold tolerance and metabolism of red-haired pine bark beetle Hylurgus ligniperda(Coleoptera: Curculionidae) during the overwintering period

Hylurgus ligniperdainvaded Shandong, China, through imported forest timber, posing a threat to China’s forest health. Exotic insects with broad environmental tolerance, including low temperatures, may have a better chance of surviving the winters and becoming invasive. Understanding the cold-tolerance strategies of H. ligniperdamay help to design sustainable pest management approaches. In this study, we aim to investigate the cold-tolerance ability and relevant physiological indicators in overwintering H. ligniperdaadults to determine any possible overwintering strategies. Supercooling points (SCPs) for adults H. ligniperdadiffered significantly across months and reached the lowest level in the mid- and post-overwintering period, the minimum SCPs −6.45 ± 0.18 °C. As the cold exposure temperature decreased, the survival rate of adults gradually decreased, and no adult survived more than 1 day at −15 °C, and the LLT50for 1 day was −7.1 °C. Since H. ligniperdaadults can survive internal ice formation, they are freeze-tolerant insects. Throughout the overwintering period, the SCPs and the water, protein, sorbitol, and glycerol content in adults decreased initially and then increased. We reported significant correlations between total protein, sorbitol, trehalose, and glycerol content in the beetles and SCPs. Glycogen, lipid, protein, trehalose, and sorbitol content in adult beetles may directly affect their cold-tolerance capacity and survival during winter. This study provides a physiological and biochemical basis for further study of metabolism and cold-tolerance strategies in H. ligniperdaadults, which may help predict population dynamics and distribution potential of pests.