Researchers from Rice University in Houston, Texas have just discovered a new species of gall wasp - one that lays its eggs in the galls of other wasps.
Gall wasps, also known as gallflies, got their name from the "gall" they leave on plants like live oaks. When these small insects leave their eggs on leaves or stem, they also inject the host plant with a chemical that creates a tumor-like growth, or the gall, which serves as a shelter for the eggs and nutrition once the wasp larva hatches.
Scott Egan, an evolutionary biologist and associate professor of biosciences at Rice University, discovered the new species a short distance from his laboratory. He describes these insects as "ecosystem engineers," explaining that the galls they create harbors a number of other species of insects, mostly invasive and parasitic by nature. The live oak trees near his laboratory provided a setting for observing these kinds of behavior, providing insights on how different species competing for resources drive evolutionary changes.
A Parasite of a Parasite
The latest species discovered is the Allorhogas gallifolia, one of four new wasp species from the genus Allorhogas detailed in a report submitted in the journal Insect Systematics and Diversity published earlier this month. Egan collaborated with researchers Ernesto Samacá-Sáenz and Alejandro Zaldívar-Riverón from the National Autonomous University of Mexico (UNAM) in Mexico City.
"They lay their egg in another wasp's gall," Egan said of the new gall wasp species, which was first hatched by his team six years ago. He explained that this species uses the gall as a resource. While the exact mechanism of its presence in another wasp's gall remains unclear, Egan suggested that these new wasps also attack the herbivorous caterpillars that eat the host tree's gall tissues, with the wasp larva later feasting on the caterpillars after they hatch.
Researchers have also proposed a number of hypotheses on how A. gallifolia interacts with other creatures on the stage that is the galls made by the Belonocnema treatae wasp. Egan shared that this new species might simply be phytophagous - dining only on plant material - or it might also be making its own galls.
"I'm convinced that these guys are predators of caterpillars that live inside the Belonocnema galls and eat the gall plant material," Egan explained. "I think the larval wasp eats the caterpillar and then emerges out of the side of the gall."
Identifying More Wasp Species
The Rice University researcher also noted that more than 50 different species from the genus Allorhogas have already been discovered across Central America and Mexico. However, in the United States, only two of these species have been documented in previous efforts - one from a 1912 effort from the University of Maryland, while the other was at a later date in Arizona.
For the new wasp species A. gallifolia, it was collected as a part of an ongoing study to identify the natural enemies for another species of gall wasp, Belonocnema treatae. Researchers in the Rice laboratory studies the creatures from the galls and catalogues them. As a "factory of discovery," as Egan describes it, the A. gallifolia was one of the mysteries that came out of the operation.
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He shared that when it was first found, it did not match any of the previously described species, prompting them to raise the possibility of an entirely new species. Soon after, Samacá-Sáenz contacted them for a collaborative effort in confirming their hypothesis.
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