Many gall wasps follow a peaceful path to adulthood, crafting themselves miniature crypts in oak tree branches where they bunker down before emerging in the spring. But a newly discovered parasitic wasp, called Euderus set, has other ideas. These ruthless insects lay eggs inside the gall wasps' home, where the larva then go on to eat their way through the host's insides, out of its head casing and into the world.
Researchers at Rice University describe the freshly discovered parasitic wasp in a paper published earlier this month. Belonging to the genus of parasitic wasps Euderus, the second part of its name is inspired by the Egyptian god of evil and chaos Set, who trapped his brother in a crypt, murdered him and chopped him into little pieces. Accordingly, the scientists have nicknamed the wasp "crypt-keeper."
The female crypt-keeper wasp wreaks havoc on the gall wasp's springtime plans, simply by laying eggs in its crypt. From there, the larva actually tricks the maturing gall wasp into making its escape hole too small, so when the gall wasp does try to emerge from the crypt, its head becomes lodged in the opening. The crypt-keeper then devours its internal organs, slips through its body and emerges through its head case.
The scientists are a little unclear on how the crypt-keeper wasp is able to manipulate the host's behavior, but they are sure that it does so. To see how well the crypt-keeper can tunnel on its own, the team taped thin strips of bark over dead gall wasp heads and waited. It observed that the crypt-keeper was around three times as likely to die in the crypt if it had to do all the digging on its own.
"It could be the parasitoid cues hosts to excavate early, but makes them do it less well than usual," said Rice evolutionary biologist Kelly Weinersmith, who studies parasites. "They only go part way and then they get stuck. That's what I love about parasite manipulation of host behavior. So many of the stories that have been uncovered are just as cool as the coolest science fiction movie."
From here, the scientists hope to discover the mechanisms used by the crypt-keeper wasp to alter the host's behavior, possibly by using CAT scans of the branches in various stages. And because E. set belongs to family of close to 600 species across North America, many of which serve as biocontrol agents for agricultural pests, the team would also like to learn if these manipulations are more widespread.
The team's latest research on the matter was published today in the Proceedings of the Royal Society B, and you can hear from the scientists in the video below, including Rice professor Scott Egan's take on the matter: "That's inherently a horror story that makes you happy not to be an insect."
Source: Rice University