This Bizarre Parasitic 'Love Vine' Turns Wasps Into Mummies

The galls in which the gall wasps develop with the love vine attached. Credit: Brandon Martin/Rice University

Nature is full of fascinating interactions between plant and animal species. Now scientists have documented, for the first time, a parasitic vine latching onto and feeding off structures created by parasitic wasps to house their larvae—leaving a mummified insect corpse inside.

Students of evolutionary biologist Liam Egan from Rice University found evidence of the wispy orange love vine (Cassytha filiformis) curling itself around the spherical, tumor-like growths produced by gall wasps on the underside of oak leaves.

"I had never seen this," Egan said in a statement. "But the fact that no one, as far as we know, had ever documented this was incredible because biologists have studied each of these—the vines and the insects—for more than a century. Basically, you have a parasitic plant attacking a parasitic insect inside of another host, a host they share," he said.

The new finding—which has been detailed in a paper published in the journal Current Biology—could even have implications for developing better cancer treatments. This is because the spherical constructions created by the wasps, known as galls, are like tumors in many ways.

"The wasps induce them to grow at the site where they lay their eggs, but the galls are part of the tree," he said. "The cells there have the same DNA as any other cell in the tree. They've just been reprogrammed to grow and behave in a way that is ultimately harmful to the tree."

If scientists were able to determine how the love vine identified and targeted the galls, it may lead to similar discoveries when it comes to targeting and fighting cancer.

Gall-forming wasps are among 13,000 insect species around the world that use biochemistry to trick trees and other plants into growing their nurseries for them.

The species in question, known as Belonocnema treatae, is native to Texas and Florida and lays its eggs only on the underside of newly growing oak leaves. When it does this, the wasp also releases a mixture of venom and proteins which disrupt the leaf's growth and induce it into producing a smooth sphere of hard brown material around the egg.

This gall provides nutrients for the larval wasp, which are drawn directly from the tree's vascular network, until the insect is mature enough to emerge.

In 2017, co-author of the study Glen Hood gathered multiple samples of galls created by Belonocnema along a 1,000-mile route winding through Florida. Students of Egan were sorting through the samples when one of them, Linyi Zhang, noticed the strange S-shaped twist of a love vine, growing around some of the galls.

Egan was unconvinced that the vine was interacting with the galls, but after cutting it open, he found a fully mature mummified wasp inside. The group then sorted back through the material and found several similar samples. In the following months, they found dozens more, including examples of the vines attacking other species of gall-forming wasps.

"We found the vines attached to galls that were slightly larger than average," Egan said. "That means the vine is either only attacking larger galls, or the vine is inducing the galls that it attacks to grow bigger, perhaps to draw more energy from them."

According to Egan, it's possible that similar interactions are taking place between many other species.

"This is the first time anyone has ever discovered a parasitic plant and parasitic gall wasp interacting on a shared host plant," he said. "This could be unique, but biologists have catalogued more than 1,300 species of gall-forming wasps and more than 4,000 species of parasitic plants, so this could just be the tip of the iceberg."