Corazonin mediates photoperiodically induced diapause in the bean bug <i>Riptortus pedestris</i>

Insects in mid- to high latitudes predict unfavorable seasons through changing photoperiod, and undergo diapause to survive harsh conditions. The circadian clock and brain neurosecretory systems are key components in regulating photoperiodic diapause. However, the neuronal pathways linking these systems, and the neuropeptides involved in photoperiodic diapause, remain poorly understood. We investigated the role of corazonin (CRZ), a conserved neuropeptide regulating metabolic stress and reproduction, in the bean bug Riptortus pedestris, a species highly sensitive to short days for diapause induction. RNA interference demonstrated that Crz-downregulated females significantly averted diapausing phenotypes even under short-day conditions, exhibiting developed ovaries and oviposition, indicating the suppressive effects of Crz on reproduction in photoperiodic diapause. Immunohistochemistry identified three distinct groups of CRZ-immunoreactive (-ir) neurons in the protocerebrum. Of these, CRZ-d cells in the pars lateralis (PL) project axons toward the corpus cardiacum-corpus allatum complex and aorta, indicating a neurosecretory role in diapause induction. Additionally, we revealed potential neural connections between CRZ-ir and pigment-dispersing factor (PDF)-ir neurons in the dorso-lateral protocerebrum. The PDF-ir neurons project neurites into/near the accessory medulla (AME), a probable hub for circadian clock regulation, suggesting that photoperiodic information processed in the AME is relayed to CRZ-ir PL neurons. PCR detected Crz receptor expression in the fat body and ovary, suggesting that CRZ-d PL neurons regulate reproductive diapause by directly targeting these tissues in response to photoperiodic inputs. These findings illuminate the neuroendocrine mechanisms underlying photoperiodic reproductive diapause in R. pedestris, highlighting the suppressive role of CRZ under short-day conditions.