Changes in the supercooling ability of Holotrichia oblita (Coleoptera: Scarabaeidae) under low-temperature stress

The scarab beetle Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae) is an economically significant subterranean pest in northern China. Studying the cold tolerance of this pest can elucidate its overwintering survival strategies, thereby providing a scientific basis for predicting its populations and developing precise overwintering control measures. In this study, we evaluated the supercooling capacity of H. oblita at various developmental stages, including larval instars, egg, pupa, and adult stages for males and females. We also examined survival rates and changes in supercooling ability under low-temperature stress. Our research found that SCPs varied significantly across developmental stages, and the lowest SCPs occurred in larvae, followed by pupae, eggs, and adults. However, no significant differences were found between the SCPs of H. oblita pupae or between male and female adults. For larvae of different day-ages, the mean supercooling points (SCPs) ranged from -3.74 to -5.37 °C. After exposure to low temperatures, the SCPs of third instar larvae ranged from -8.0 to -1.6 °C. The median lethal temperature of third instar larvae was -1.27 °C. The results of our study show that H. oblita is a cold-intolerant insect. While this species has limited cold tolerance, it burrows deep into the soil in the winter and therefore is unlikely to be exposed to lethal temperatures. This study offers insights into the overwintering strategies of H. oblita and provides a foundation for predicting larvae overwintering populations.