Ghoulish New Wasp Species May Be a 'Parasite of a Parasite'

Just in time for Halloween, researchers have announced the discovery of a new wasp species that appears to have some rather ghoulish tendencies. Found on the Rice University campus in Houston, the new wasp seems to act as a “parasite of a parasite.”

Evolutionary biologist Scott Egan, as associate professor of biosciences at Rice, studies gall wasps, which he describes as a “strange version of a herbivore.” When the tiny insects lay their eggs on oak leaves or stems, they also create a mixture of venom and proteins to trigger the trees to form odd, tumor-like growths, called galls. The larva grows inside the galls, feeding on the tumor until emerging as an adult.

There are many insects and other invertebrates that use the galls as resources, Egan tells Treehugger. Most are predators called parasitoids that attack the gall wasp inside. Some are  insects called inquilines that feed on the nutrient-rich gall tissue. Then there are insects that attack both the predators and inquilines. Those are called hyperparasitoids.

Egan and his team discovered four new wasp species — one on the Rice campus and three others across the Gulf Coast — that are natural enemies of the gall wasp. 

“The four new wasp species we discovered are in the genus Allorhogas, and we think they are hyperparasitoids that are attacking a gall-tissue-eating caterpillar commonly found in our galls,” Egan says.

More than 50 species of Allorhogas have been discovered in Central America and Mexico, but only two species were documented previously in the U.S.: one at the University of Maryland campus in 1912 and another years later in Arizona.

A Resourceful Parasite

The newly discovered wasp acts as a parasite, laying its eggs in another wasp’s gall. Things appear to get a little insidious after that, but it’s only a hypothesis at this point, Egan says.

"They're using the gall as a resource, and we're still not certain how, but I think they're attacking herbivorous caterpillars that are feeding on the gall tissue, and the wasp larva are eating those caterpillars after they hatch,” he says.

Egan and his team described the new species in a study in the journal Insect Systematics and Diversity.

There are more than 1,400 known species of gall-forming wasps, and Egan says he believes there are many more species waiting to be discovered. He calls the wasps “ecosystem engineers,” because they modify their environment and have such an impact on the species diversity in the area.

“I find gall wasps fascinating for a million reasons. First, they manipulate the stem cells of another organism, their host tree, to grow them a home. How crazy is that?” he says.

“Once you know how to identify a gall, you will realize they are everywhere. I have them in my yard at home, right out the front door of my lab, and everywhere in between. I live in an active laboratory where new observations can be made any day.”