A horrifying insect soap opera with vampires, mummies and infant-eating parasites is playing out on the stems and leaves of live oak trees every day, and evolutionary biologist Scott Egan found the latest character—a new wasp species that may be a parasite of a parasite—within walking distance of his Rice University lab.
Egan, an associate professor of biosciences at Rice, studies gall wasps, tiny insects that cast a biochemical spell on live oaks. When gall wasps lay their eggs on oak leaves or stems, they chemically program the tree to unwittingly produce a tumor-like growth, or gall, which first shelters the egg and then feeds the larval wasp that hatches from it.
Egan describes the wasps as “ecosystem engineers,” because their galls are attractive morsels that harbor a supporting cast of opportunistic ne’er-do-wells, thieves and killers. It’s a great setting to study how competition for resources drives evolution, and Egan and his students have spent more than a decade documenting the eerie, interspecies who’s-eating-who drama.
The latest species they discovered at Rice, Allorhogas gallifolia (al-UHROH’-guhs GAHL’-ihf-ohl-eeuh), is one of four new wasp species from the genus Allorhogas that Egan and collaborators Ernesto Samacá-Sáenz and Alejandro Zaldívar-Riverón at the National Autonomous University of Mexico (UNAM) in Mexico City described in a study this month in Insect Systematics and Diversity.
“They lay their egg in another wasp’s gall,” Egan said of A. gallifolia, which his group first hatched in 2014. “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 said more than 50 species of Allorhogas have been found in Central America and Mexico, but only two species were previously documented in the United States, one at the University of Maryland campus in 1912 and another some years later in Arizona.
The A. gallifolia found at Rice was collected as part of an effort to describe the community of natural enemies for one