An RNAi-Based Vulnerability in the White-Backed Planthopper: Silencing SfHSP70-8 Impairs Thermotolerance and Insecticide Susceptibility in a Key Rice Pest

Heat shock protein 70 (HSP70) serves as a critical molecular chaperone governing environmental stress responses in insects. This study aimed to characterize the expression pattern of SfHSP70-8 and determine its functional role in thermotolerance and insecticide susceptibility in the white-backed planthopper, Sogatella furcifera. Here, we cloned and characterized SfHSP70-8, a cytosolic member of the HSP70 family from S. furcifera. The encoded protein contains characteristic conserved domains and shares close sequence identity with the HSP70 homolog of Laodelphax striatellus. Spatiotemporal expression profiling revealed ubiquitous transcription across all developmental stages, peaking in third-instar nymphs, and pronounced enrichment in the gut and fat body. Transcript levels were robustly elevated following exposure to both thermal extremes (10–40 °C) and LC50 concentrations of triflumezopyrim, sulfoxaflor, and imidacloprid. RNAi-mediated silencing of SfHSP70-8 significantly compromised tolerance to triflumezopyrim and sulfoxaflor while leaving imidacloprid susceptibility unchanged, and markedly decreased survival rates under chronic heat stress at 30 °C and 35 °C. Collectively, these findings demonstrate that SfHSP70-8 functions as an essential regulator of thermotolerance and insecticide adaptation in S. furcifera, offering a potential molecular target for future development in sustainable pest management.