Compatible invasion of a phylogenetically distant host embryo by a hymenopteran parasitoid embryo.

Embryonic invasion into the tissue of genetically different organisms has been known only in mother-embryo interactions of viviparous organisms. Hence, embryonic invasions have been thought to occur only within the same or closely related species. For endoparasitic Hymenoptera, which are oviposited in their host egg but complete their development in the later stages, entry into the host embryo is essential. To date, the entry of these parasitoids is known to be accomplished by either egg deposition directly into the embryo or by the newly hatched larva boring into the embryo. However, Copidosoma floridanum is a polyembryonic parasitoid whose development is characterized by a prolonged embryonic stage, and which lacks a larval form during its host embryogenesis. We have analyzed the behavior and fate of C. floridanum embryos co-cultured with their host embryo in vitro. Here, we show that the morula-stage embryo of C. floridanum actively invades the host embryo. Histological analyses have demonstrated that C. floridanum embryonic invasion is associated with adherent junction to host cells rather than causing an obvious wound on the host cells. These findings provide a novel case of embryonic invasion into a phylogenetically distant host embryo, ensuring cellular compatibility with host tissues.