Heat Acclimation-Mediated Phenotypic Plasticity Enhances Thermal Tolerance by Regulating HSP20 Family Genes in Phyllotreta striolata

Climate warming is increasing the frequency and intensity of extreme heat events, imposing strong thermal constraints on pests while potentially selecting for enhanced heat tolerance. Phyllotreta striolata (Fabricius) is a Eurasian-origin pest of cruciferous vegetables with a broad distribution extending from temperate to tropical regions; however, the mechanisms enabling its persistence under sustained high-temperature conditions remain poorly understood. Here, we investigated the time-dependent effects of heat acclimation on thermal tolerance in adult P. striolata using Static heat knockdown time (HKDT) and dynamic critical thermal maximum (CTmax) assays and examined the molecular basis of acclimation through transcriptomic profiling after 96 h of heat exposure. Heat acclimation enhanced thermal tolerance in both assays, although the response emerged earlier under dynamic than static conditions (72 h versus 84 h) and peaked after 96 h of acclimation before weakening at 108 h. Transcriptomic analysis of 96 h-acclimated adults revealed extensive remodeling of metabolic and stress-response pathways, including pronounced induction of HSP genes. Quantitative PCR identified psHSP201–psHSP204 and psHSP701 as strongly heat-responsive candidates, and RNA interference-mediated silencing of selected HSP genes, particularly HSP20 family members, reduced heat tolerance. These findings reveal a temporally optimized heat-acclimation response in P. striolata, identify HSP20 genes as important contributors to acquired thermotolerance, and provide candidate targets for RNAi-based management of this pest under a warming climate.