Do 'glanduliferous' larvae of Galerucinae (Coleoptera : Chrysomelidae) possess defensive glands? A scanning electron microscopic study

摘要

Larvae of the chrysomelid taxon Galerucinae, Sermylini, are known to release a fluid from dorsolateral segmental openings when disturbed. The release of this fluid resembles the discharge of secretion from well-studied exocrine defensive glands in larvae of Chrysomelinae, the putative sister group of Galerucinae. Thus, Sermylini larvae have been named "glanduliferous" ones. However, no comparative analyses of the internal structures of the segmental openings in Sermylini larvae have been available prior to this study. Therefore, segmental larval openings in 10 Sermylini species were investigated by scanning and light microscopy. Two types of segmental openings were detected: (1) the opening is visible as an integumental slit which can be opened and closed by muscles. No specific glandular structures are associated with this slit. (2) The opening is covered internally by a cuticular sac which can be everted to the outside. A cuticular duct of a gland is leading into this sac. Haemolymph is discharged from both types of openings. These structures are discussed with respect to reflex bleeding in other taxa. Furthermore, a common origin of the segmental openings in larvae of Sermylini and the segmental exocrine glands in chrysomeline larvae is critically questioned.