Effects of long-term thermal stress on population dynamics and HSP70 expression of Hyphantria cunea (Lepidoptera: Erebidae)

Hyphantria cunea (Lepidoptera: Erebidae), a globally significant quarantine pest, is facing thermal stress during its southward expansion in China. Heat shock protein 70 (HSP70) family members serve as key components in insect molecular networks under heat stress. However, studies remain limited on this pest's tolerance to persistent high temperatures and the role of HSP70 under such stress conditions. In this study, extreme heat treatment (EHT; daily cycle of 31 °C (6 h), 34 °C (6 h), 37 °C (6h), and 34 °C (6 h)) drastically reduced H. cunea larval survival, preventing life cycle completion. Heat treatment (HT; daily cycle of 28 °C (6 h), 31 °C (6 h), 34 °C (6 h), and 31 °C (6 h)) during early stages had minor effects on larval development, whereas exposure during late larval stages shortened developmental duration, reduced fecundity, and decreased fitness. To explore the molecular mechanisms, four HSP70 genes of H. cunea were cloned and characterized. Phylogenetic analysis revealed high conservation among HcHSP70s, showing a close relationship with those from Noctuidae insects. HcHSP70 transcripts were significantly upregulated during heat stress, exhibiting diurnal fluctuation with peak expression at specific times. These results show that H. cunea can tolerate moderate heat stress, but pre-reproductive thermal stress reduces fecundity. The upregulation of HSP70 expression contributes to enhanced thermotolerance in this pest. Overall, this research provides a reference for population prediction of H. cunea in regions with increasing heat stress.