Energy Consumption and Cold Hardiness of Diapausing Fall Webworm Pupae

SIMPLE SUMMARY: The fall webworm, Hyphantria cunea, a major invasive pest in China, overwinters as diapausing pupae, but seasonal changes in energy consumption and cold hardiness of diapausing pupae are still unclear. In this study, we investigated the seasonal variation in lipid, glycogen, and trehalose content accompanying changes in the supercooling points of diapausing pupae. We found that the energy consumption of H. cunea diapausing pupae was dominated by lipid and carbohydrates early in diapause and shifted to glycogen or other energy stores as diapause progressed. We also found that an increase in pupal diapause development time had a significant negative effect on the survival rate of pupae during diapause and the post diapause adult fitness. This information is essential for the development of a theoretical foundation to better understand the overwintering strategy of H. cunea and for improving forecasts of the population dynamics according to the thermal conditions in various years. ABSTRACT: Diapause and cold hardiness are essential components of winter survival for most insects in temperate zones. The fall webworm, Hyphantria cunea, overwinters in a pupal diapause. In this study, we investigated the energy consumption and cold hardiness of diapausing pupae. We found that lipid content decreased from October to November and stabilized from November to March. Glycogen content decreased by 61.3% and 52.2% for females and males, respectively, from October to November, and decreased slowly from November to March. We also observed a significant increase in trehalose concentrations as ambient temperatures decreased from October to November and a decrease in trehalose as temperatures increased again in March. We did not observe substantial changes in pupal supercooling points among the dates sampled. In addition, prolonged pupal development time reduced their survival rate and had no significant effect on post-diapause adult body mass and fecundity but reduced egg diameter in females. These results suggest that the energy consumption of H. cunea pupae during early diapause depends on lipid and glycogen, while it shifts to depend on glycogen or other energy stores in the mid- and late diapause stages. Our results also suggest that the prolonged development time of diapausing pupae had a negative effect on post-diapause fitness.