The Vine That Loves Parasitic Wasps to Death

[♩INTRO] “The love vine” seems like a strange nickname for a parasitic plant especially one that can be so demanding of its hosts that they die. But it’s counterintuitive name isn’t what makes it unique. Instead, it’s special because it’s the only organism we know of that sucks the life out of plants and their insect parasites simultaneously. Seems...kind of... straight out of a horror movie. In nature, certain wasps, flies, and other parasitic insects manipulate plants into producing galls, tumor-like growths full of tasty, nutritious plant material. To do it, females lay their eggs on or in the plant in question, along with a special chemical cocktail that triggers the plant to start forming a gall. The size, shape, and content of the growths is chemically controlled by the parasites, so they can force their host to make perfect little nurseries. And the gall’s exterior is both tough and loaded with noxious chemicals, so not many animals are able to break through to the vulnerable larva inside. But Cassytha filiformis is no animal. It’s a vine. It’s so common in tropical environments worldwide that people from many cultures have used it medicinally and mystically for centuries. That’s actually where its common name “the love vine” comes from its supposed utility is as an aphrodisiac. For a while, this vine was thought to prey solely on other plants for physical support, water, and nutrients. Then, researchers saw something weird. In 2018, scientists studying gall-forming wasps in Florida discovered love vines wrapped around nearly 60 of the galls of one wasp species they’d collected. Nearly half of those galls contained dead, mummified adult wasps, while only 2% of vine-less galls did. That strongly suggests that the vines steal from the insects as well as the tree. Now, it does make sense that the vines would feed on galls they’re basically juicy, starchy cancers. They’re perfect snack even without a protein-packed larva inside. And unlike with most animal predators, the outer gall casing is no obstacle for the love vine. It already steals from its host using haustoria, which are kind of like specialized roots. They can tunnel through thick bark to find a tree’s juiciest tissues, so they have no trouble worming their way through the tough shells of galls. But the fact that they also nom on the wasps was a little more unusual. And once the team started looking, they found the vine sucking the life from several other species of gall-forming parasites, too. Through other observations, they even realized the vines weren’t stumbling upon the galls by accident. But that’s not the weirdest part. The parasitized galls were also 35% larger. So either the vines selectively target large galls… or they somehow make the galls they’re feeding from grow. They could be tricking the insects into tricking the trees into making bigger galls. As unlikely as that sounds, the fact that the dead wasps inside vine-attacked galls were adults could actually support the idea. If nothing else, that shows the vines take their time to let the insects develop before sucking them dry. So far, the love vine is the only parasite we know of that attacks its hosts’ parasites in this way. But there are thousands of parasitic plants and tens of thousands of gall-forming insects. If it took this long to notice this vine’s thirst for flesh, there could be dozens or even hundreds of parasitic plants just waiting for their carnivory to be revealed. Thanks for watching this episode of SciShow! If you’d like to learn another bizarre fast fact, you can watch our episode about this baller rat that kicks rattlesnakes in the face! Or you can go to youtube.com/scishow to subscribe. [♩OUTRO]

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