Parasitic Vines That Feed on Parasitic Wasps That Feed on Trees

Original source: https://www.nytimes.com/2018/08/30/science/parasitic-vines-wasps.html

Author: Paloma López Laiz

What if a parasite got a taste of its own medicine? Used to a stress-free way of living, in which they profit from unsuspected hosts, what if the tables were turned on them? New research has shown that this is possible: a vine tree that feeds on parasitic wasps that feed on oak trees.

The affected parasite is a wasp whose larvae develop in a gall—swollen masses of oak tissue that provide nutrients to the larvae—until they are mature enough to leave. Scientists studying these wasps have found out that a vine feeds on the gall, preventing the wasps’ development. This is known as a second parasite.

At first, the main researcher, Scott Egan, thought that it had to be a mistake, because it looked very strange. Then, he imagined it could be a seed or a fruit. But when he cut it open, he found a wasp inside, so he started to look through the samples gathered and realised that it wasn’t an isolated case.

Oak tree galls — compartments of plant tissue containing wasp larvae — with a parasitic vine attached by tiny wooden suction cups. Credit: Brandon Martin/Rice University

Dr Egan then decided to travel to the Florida sand live oak forest, where his collaborator, Glen Hood, first found the gall. Soon, he realised that the oaks were threaded with a vine called love vine.

After studying many love-vine-infested galls from one wasp species, they found out that 45% of all of them had a mummified adult specimen. This suggested that the wasp was able to form fully but was unable to leave this structure due to the vines’ stealing of the nutrients.

The vine attaches usually to stems, buds, and the tops and sides of leaves, but never to the underside, which is where the gall is formed. This distaste for the underside changes when there is a gall, which suggests that they may be attracted to these tissues or that the gall changes enough the leaf so that attachment of the vine is allowed.

A closer view of the suction cups which the parasitic love vine uses to attach itself to the galls. Credit: Scott Egan and Matt Comerford/Rice University

And what about the oak trees? It seems that they are minimally affected: they produce fewer acorns and reproduce less. However, a long-standing study has shown that they are green and flowering and still generate acorns. It seems that the host can stand to live with a parasite and still survive. In this case, it is the first parasite the one who gets the shortest end of the stick.