The Strepsipteran, Xenos vesparum is a parasite of a paper wasp, Polistes dominulus. Males have a lifecycle typical of most insects with egg, larva, pupa and adult stages. Female larvae have an unusual lifecycle in which they molt to a fourth instar that is paedogenic (capable of reproduction as a larva). There is no molt to pupa or adult.
Mature female larvae will partially exit the host with only the sclerotized portion of the head + thorax extruded between the abdominal segments of the wasp. Larvae lack the external reproductive structures found in most insects. Instead, mature female larvae contain a structure called the brutkanal (brood canal or ventral canal). The ventral canal is the long dark structure in the image (left). This canal opens to the outside anteriorly to allow insemination. Internal ducts allow sperm move from the brutkanal to the hemocoel and eventually the ovaries where eggs are fertilized. Eggs develop and larvae hatch within the female. The larvae are triangulate (have legs) and move through the hemocoel into the brutkanal and exit the female. Newly emerged larvae may wait on flowers and spread to new wasp hosts in uninfested colonies.
*L. Beani, F. Giusti, D. Mercati, P. Lupetti, E. Paccagnini, S. Turillazzi, and R. Dallai. 2005. Mating of Xenos vesparum Revisited. JOURNAL OF MORPHOLOGY 265:291–303.