On the articulation of the pierid silk girdle

Abstract

ABSTRACT Many Lepidoptera secure their pupae to environmental substrates using a dual attachment system that consists of a cremaster and silk girdle. Although the cremaster has received a lot of attention because of its morphological complexity, the silk girdle is generally assumed to be just a loop of silk loosely encircling the pupa. Here, using Catopsilia pomona as a pierid model, it is shown that the articulation of the girdle with the pupal cuticle is precisely locked into the cuticle by a three-point system that consists of: (1) a groove on A1; (2) a notch produced by the lateral lip of the groove structure; and (3) ‘wire-bite’ across the lateral margins and dorsal wing buds of the pupae. The former two are anatomical, the latter involves subdermal embedding of the girdle into the cuticle during ecdysis. These three points of articulation restrict anterior-posterior, but not lateral, freedom of movement. Cuticular incorporation ensures the attachment is itself unyielding. Observations of pre-pupal ecdysis were used to ontogenetically pinpoint and describe the embedding process. This interaction with and involvement in the suspensory mechanism highlights an unnoticed role for moulting in lepidopteran metamorphosis.