Corazonin mediates photoperiodically induced diapause in the bean bug Riptortus pedestris

Area of Science:

• Neuroscience
• Insect Physiology
• Endocrinology

Background:

• Insects use photoperiod cues to anticipate unfavorable seasons and enter diapause for survival.
• Circadian clock and neurosecretory systems regulate photoperiodic diapause, but neuronal pathways and neuropeptides involved are not fully understood.

Purpose of the Study:

• To investigate the role of corazonin (CRZ) in regulating photoperiodic reproductive diapause in the bean bug Riptortus pedestris.
• To elucidate the neuroendocrine pathways linking circadian clock and neurosecretory systems in diapause induction.

Main Methods:

• RNA interference (RNAi) to downregulate Crz expression in female bean bugs.
• Immunohistochemistry to identify CRZ-immunoreactive neurons and their projections.
• Polymerase Chain Reaction (PCR) to detect Crz receptor expression in various tissues.

Main Results:

• Downregulation of Crz prevented diapause phenotypes in short-day conditions, with females showing developed ovaries and oviposition.
• Three distinct groups of CRZ-immunoreactive neurons were identified, with specific neurons projecting to neurosecretory organs.
• Neural connections between CRZ and pigment-dispersing factor (PDF) neurons were observed, suggesting a link to circadian clock regulation.
• Crz receptor expression was detected in the fat body and ovary, indicating direct regulation of reproductive diapause.

Conclusions:

• Corazonin plays a crucial role in suppressing reproduction and inducing diapause under short-day conditions in R. pedestris.
• CRZ-producing neurons in the pars lateralis likely act as neurosecretory cells, relaying photoperiodic information to target tissues.
• This study reveals novel neuroendocrine mechanisms underlying photoperiodic reproductive diapause, highlighting the function of CRZ in seasonal adaptation.