Functional morphology of the genitalia of Rhyacophila lezeyi Navas, 1933 (Trichoptera, Rhyacophilidae)

We collected seven fixed pairs of Rhyacophila lezeyi during mating copulation and observed four different states of copulation. We investigated the underlying mechanism for the variations in the morphology of each copulating device, based on the copulation state. Notably, the male anal sclerites underwent considerable changes from the early stages of copulation. Initially, the female segment VIII approached the male anal sclerites, which were pushed downwards by the female VIII and IX segments, extending from IX. With the progression of mating stage, the distended end of the female’s segment VIII covered the anal sclerites, pushing them further down. The male parameres were initially folded in bellows-like shapes under the aedeagus before copulation initiation. However, as the copulation stage advanced, they extended to about 3.2 times of their original length. Distended ends of both parameres adhered to the position of the spiracles at the anterior margin of the lateral part of the female’s VII abdominal sternite. The attachment site was the external surface of the hair bulb of the male parameres. During the middle stage of copulation, movements involving the opening and closing of the male gonopods started. The gonoslylus made strong contact with the female’s abdominal segment VIII, resulting in the deformation of segment VIII due to the contact pressure.