Expression and RNAi characterization of neuropeptides and signaling pathways 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,
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
differences in mortality, larval weight, or defoliation were detected
following dsRNA-mediated knockdown of GPA2 or LGR1 via injection or
feeding. However, 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
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.