Brain-independent development in the moth Sesamia nonagrioides

Area of Science:

• Insect endocrinology
• Developmental biology
• Insect physiology

Background:

• Photoperiod (long-day vs. short-day) significantly impacts the developmental trajectory of Sesamia nonagrioides caterpillars, influencing pupation and diapause.
• Larval development in insects is tightly regulated by hormonal cues, including juvenile hormone (JH) and brain-derived factors.

Purpose of the Study:

• To investigate the role of the brain and other head factors in regulating larval molting, pupation, and imaginal development in Sesamia nonagrioides.
• To elucidate the interplay between photoperiod, brain activity, corpora allata (CA), and juvenile hormone (JH) in controlling developmental transitions.

Main Methods:

• Surgical manipulations including brain removal (debraining) and decapitation of larvae under different photoperiodic conditions.
• Experimental implantation of brains and application of juvenile hormone (JH) agonists.
• Isolation of larval abdomens to assess autonomous developmental capacity.

Main Results:

• Larval molts, including extra molts, can occur in Sesamia nonagrioides larvae even after brain removal, particularly under short-day conditions or with JH agonist application.
• Pupation and imaginal development are promoted by brain removal in 6th instar larvae, but some debrained larvae still undergo larval molts.
• Decapitation generally induces pupation, but this can be reverted to a larval molt by JH agonist treatment, suggesting complex hormonal interactions.

Conclusions:

• The brain exerts both stimulatory and inhibitory influences on developmental timing and molting in Sesamia nonagrioides, affecting corpora allata (CA) activity.
• A brain-independent head factor, distinct from the brain itself, appears necessary for the pupal-adult molt.
• The capacity for larval molts in the absence of the brain and CA suggests significant persistence or endogenous production of juvenile hormone (JH).