SfHsp20.2 is required for male fertility by controlling eupyrene sperm bundle morphogenesis and sperm migration in the fall armyworm

Abstract BACKGROUND The fall armyworm, Spodoptera frugiperda , is a destructive pest threatening global food security. The sterile insect technique (SIT) is a promising eco‐friendly control strategy, which relies on exploring genes regulating male fertility. Small heat shock proteins (sHSPs) act as molecular chaperones and participate in insect reproduction, yet their roles in lepidopteran dimorphic spermatogenesis remain poorly understood. RESULTS Here, we functionally characterized a testis‐enriched sHSP gene, SfHsp20.2 , in S. frugiperda . Using CRISPR/Cas9‐mediated knockout, we found that loss of SfHsp20.2 caused severe morphological defects in eupyrene sperm bundles and reduced the abundance of apyrene sperm bundles. Mutant sperm could be transferred normally to the female bursa copulatrix but failed to migrate to the spermatheca, eventually leading to male‐specific near‐sterility. Transcriptome analysis revealed that SfHsp20.2 mutation disturbed energy metabolism and stress response pathways in testes. CONCLUSION Our results demonstrate that SfHsp20.2 is essential for dimorphic sperm development and sperm migration. This gene represents a potential candidate target for SIT‐based management of S. frugiperda . © 2026 Society of Chemical Industry.