Traumatic insemination and female counter-adaption in Strepsiptera (Insecta)

Traumatic insemination in Strepsiptera is a disputed issue. To clarify this question the mating of Stylops ovinae (Stylopidae) was documented in detail using a combination of different techniques. A major issue is the specific mode of sperm transfer, either as a traumatic penetration of the body wall, or alternatively an insertion of the penis into the brood canal without penetration of the body wall of the female. In contrast to previous studies, we used an integrative approach. In addition to video recordings of the mating, the duration and frequency of copulation were assessed. Histological sections of virgin females and females fixed shortly after copulation were made. Micro-CT scans of fixed copulae of S. ovinae were taken and the involved structures were studied with scanning electron microscopy and reconstructed three dimensionally. We could demonstrate that an invagination with a thickened cuticle is present, directly in front of the birth opening of the female. The male inserts his penis in this invagination and its apical part perforates the ventral cuticle. Thereafter the sperm is injected into the hemocoel of the female and reaches the oocytes via the hemolymph. The invagination is a secondary genital structure, similar to the spermalege of the common bedbug Cimex lectularius (Heteroptera).