The Cocoon of the Developing Emerald Jewel Wasp (Ampulex compressa) Resists Cannibalistic Predation of the Zombified Host.

Introduction: To reproduce, the parasitoid emerald jewel wasp (Ampulex compressa) envenomates an American cockroach (Periplaneta americana) and barricades it in a hole with an egg on the host's leg. The larval wasp feeds externally before entering the host and consuming internal organs before forming a cocoon inside the host carcass.

Methods: The vulnerability of jewel wasp larvae to predation by juvenile cockroaches was investigated, and data were recorded with time-lapse videography.

Results: Cockroaches were found to be predators of parasitized hosts. When parasitized cockroaches were exposed to hungry cockroaches on days 0-8 of development, the developing larva was killed. Eggs were dislodged or consumed, larvae on the leg were eaten, and larvae inside the host were eaten along with the host. On day 9, 80% of the wasp larvae were killed and eaten along with the host. Conversely, on day 10, 90% of the larvae survived. On developmental day 11 or later, the wasp larva always survived, although the host carcass was consumed. Survival depended entirely on whether the cocoon had been completed.

Conclusion: The results highlight the vulnerability of larvae to predation and suggest the cocoon defends from insect mandibles. This may explain the unusual feeding behavior of the jewel wasp larvae, which eat the host with remarkable speed, tapping into the host respiratory system in the process, and consuming vital organs early, in contrast to many other parasitoids. Results are discussed in relation to larval wasp behavior, evolution, and development, and potential predators are considered.