Extraembryonic membranes of the endoparasitic wasp Cotesia congregata: presence of a separate amnion and serosa.

Little information is available describing the development of endoparasitic Hymenoptera prior to hatching of the first instar larva. The present study reveals that in Cotesia congregata, and likely other braconid wasp parasites, the serosa and amnion comprise separate layers encasing the developing first instar larva. Examination of newly hatched first instar parasites in the hemocoel of Manduca sexta confirmed that the larvae were ensheathed in the remnants of an "amnion" at hatching, with patches of nucleated cells seen adhering in thin sheets to the larva. The amnion is delaminated from a cellular serosal membrane that lies directly beneath the chorion, which subsequently gives rise to teratocytes. Scanning electron micrographs indicate that remnants of the amnion remained associated with the larvae for a longer period posthatch than did the teratocytes, which rapidly dispersed into the host hemolymph. The presence of an amnion-like layer in braconid endoparasitic wasps may prove to be significant with respect to our understanding of host-parasite immunological interactions occurring during the initiation of the relationship of the parasites with their host.