Transverse cuticular structures arise above actin filament bundles in the epidermis of Calpodes ethlius (Stöll) (Lepidoptera : Hesperiidae)

Abstract

Rhodaminyl phalloin labelling of larval epidermal cells in Calpodes ethlius (Stöll) (Lepidoptera : Hesperiidae) shows dorsal areas with apical bundles of F-actin. The bundles are present only during the first 36 hr of the 5th stadium. Most cells have only one or 2, rarely 3, 4 or 5. The bundles extend into the overlying cuticle as the cores of large helical microvilli that continue on as transverse cuticle components, resembling very large helical pore canals. The transverse structures are like those seen in extensible insect cuticles that may allow cuticular stretching during larval growth. Neither the bundles nor the transverse structures are easily resolvable by conventional stains for LM or EM. The results suggest that transverse fibrillar structures may be a more common component of soft cuticles than has been generally realized.