Expression and RNAi characterization of neuropeptides underlying developmental regulation in the Colorado potato beetle.

Neuropeptides are evolutionarily ancient signaling molecules that act through diverse G protein-coupled receptor (GPCR) pathways to coordinate essential physiological and behavioral processes in insects. Despite their broad functional importance, the specific roles, receptor interactions, and regulatory mechanisms of individual neuropeptides remain underexplored, limiting our understanding of how these signaling systems operate across developmental and physiological contexts. In this study, we characterized transcript expression of five functionally diverse neuropeptides and one GPCR across Leptinotarsa decemlineata (Colorado potato beetle) tissues and life stages and subsequently knocked down the glycoprotein hormone subunit alpha 2 (GPA2) and its cognate receptor with glycoprotein hormone subunit beta 5 (GPB5), leucine-rich repeat-containing GPCR 1 (LGR1), for phenotypic investigation. Expression analyses revealed broad and tissue-specific variation among neuropeptides across developmental stages. No significant patterns in mortality, larval weight, or defoliation were detected following dsRNA-mediated knockdown of GPA2 or LGR1 via injection, though in the feeding trial third instar larvae given LGR1 dsRNA weighed significantly more and showed reduced defoliation rates compared the control. State-transition modeling identified significant effects of GPA2 and LGR1 knockdown on developmental timing, specifically during pupal-adult and larval-pupal-adult transitions, respectively, with time in life stage emerging as a key predictor of overall survival. These findings suggest a potential hormonal role for the GPA2-LGR1 signaling system in regulating developmental progression and stabilizing life-stage transitions in L. decemlineata.