Derived morphology in a basal moth: The uniquely specialized sternum V glands of Agathiphaga (Lepidoptera: Agathiphagidae)

The sternum V gland is a notable specialization shared by basal Lepidoptera and most Trichoptera; it is generally present in both sexes or in females only. In both orders the secretory cells usually discharge into a sac-like reservoir from which a duct leads to the opening on sternum V. In contrast, the gland in agathiphagid moths is only present in males and it exhibits several unique specialisations: the glandular portion being the apical (morphologically anterior) part of a long tubular cuticular invagination covered with contiguous ‘type-3’ glandular units; together with the following part of the efferent duct it is coiled like a ball of yarn; the duct expands into a fusiform reservoir, and a separate small sac surrounded by a complex muscular coat is present just inside the gland opening. The principal opener muscle of each gland originates on the contralateral side of sternum VI, hence crossing its counterpart in the midline. Characters of the agathiphagid sternum V gland, the function of which remains unclear (though sex pheromone production may appear most likely), add significantly to the suite of autapomorphies exhibited by this otherwise overall remarkably generalized moth taxon.

► The agathiphagid sternum V gland is present in males only; a pheromone producer?
► The secretory portion is a slender tube separated from a fusiform reservoir.
► The secretory tube bears contiguous ‘type-3’ gland units.
► A saccular duct appendix with a muscle coat is located before the gland opening.
► The principal opener muscles of the paired glands cross in the midline.