Heat shock protein genes Hsp70 and DnaJA1 are key contributors to thermotolerance and development in predatory ladybeetle Propylaea japonica.

Global climate change has increased the frequency of extreme high-temperature events, underscoring the need to elucidate thermotolerance mechanisms in natural enemy insects for effective biological control. The ladybird Propylaea japonica is a predominant predator in South-East Asia and a successful biocontrol agent, yet the molecular basis of its heat resistance remains unknown. Here we cloned full-length cDNAs of three heat shock protein genes (pjhsp70, pjDnaJA1, and pjhsp21) from P. japonica using transcriptomic data. We characterized their sequences, inferred phylogenetic relationships, and quantified spatiotemporal expression by qRT-PCR across developmental stages, adult ages, and tissues. To assess function, we knocked down each gene with RNA interference (RNAi) and measured survival at 39 °C, male body weight, and sex ratio; we also expressed and purified the recombinant proteins to evaluate chaperone activity in vitro. The results showed that all three transcripts were detected throughout development, peaking in the pupal stage, and exhibited tissue-specific variation. RNAi of pjhsp70 or pjDnaJA1 markedly reduced survival under heat stress and decreased male weight while skewing the sex ratio; pjhsp21 knockdown produced no such effect. In vitro, recombinant pjhsp70 and pjDnaJA1 inhibited protein aggregation, confirming chaperone activity, whereas pjhsp21 lacked independent chaperone function. Collectively, these findings indicate that pjhsp70 and pjDnaJA1 are key contributors to thermotolerance and development in P. japonica, providing a molecular framework for enhancing biocontrol efficacy under high-temperature conditions.