Conditionally essential: A testis‐enriched heat shock protein from fall armyworm safeguards fertility and survival under heat stress

BACKGROUND: Extreme high temperatures significantly threaten insect development and reproduction. Small heat shock proteins (sHSPs) are crucial for thermal adaptation, but their specific roles in reproduction and heat stress response remain incompletely understood. This study investigates SfHSP19.8, a testis-enriched sHSP in the fall armyworm (Spodoptera frugiperda), to elucidate its function. RESULTS: -instar larval testes revealed dysregulation of genes in steroid hormone biosynthesis and detoxification pathways. However, knockout did not impair adult male fertility, testis morphology or sperm count under standard conditions. SfHSP19.8 expression was strongly induced by heat shock across developmental stages. Mutants exhibited severely compromised thermotolerance under heat stress, including complete egg hatching failure, high larval mortality, prolonged larval development, and reduced adult longevity and reproductive fitness. CONCLUSION: These findings demonstrate that SfHSP19.8 is essential for systemic thermotolerance across life stages and maintains reproductive function specifically under thermal challenge, while being dispensable for basal male reproduction under optimal conditions. SfHSP19.8 represents a potential target for pest control strategies in the context of future climate warming.