Laccase2-Mediated Mandibular Development Is Crucial for Larval Feeding Behavior in the Silkworm, Bombyx mori

The phenoloxidase gene Laccase2 (Lac2) is an indispensable survival gene in insects, playing key roles in cuticle tanning, exoskeleton development and pigment deposition. However, in lepidopteran insects, the roles of Lac2 in mandibular development and feeding behavior remain largely unexplored. In this study, we demonstrated that Lac2 is essential for mandibular development in early larvae of the model lepidopteran, the silkworm, Bombyx mori. We cloned and characterized BmLac2 and found that it is evolutionarily conserved in lepidopteran insects. Disruption of BmLac2 via CRISPR/Cas9 system induced mandibular defects, which directly impaired larval feeding behavior and culminated in developmental arrest and larval mortality. Moreover, knockout of BmLac2 led to dopamine accumulation during the dormancy stage, but the dopamine level returned to normal after molting, without altering feeding motivation in mutant larvae. Furthermore, RNA sequencing (RNA-seq) and quantitative real-time polymerase chain reaction (qRT-PCR) analyses revealed that loss of BmLac2 affected the expression of genes associated with cuticular formation and immunity, also contributing to larval mortality alongside feeding defects. Altogether, BmLac2-mediated mandibular development and cuticular melanization play key roles in regulating feeding behavior and immunity in early-stage silkworm larvae, making this gene a potential target for early intervention against lepidopteran pests.