The small, iridescent Ormyrus labotus always seemed suspicious of a parasitoid wasp. It wasn’t the wasp’s striking beauty — wasps can also be conventionally attractive — but its life strategy. Parasitoid wasps lay their eggs on or inside other insects and arthropods, and the larvae eat their way out when they hatch. Each parasitic wasp species tends to prefer one or a few hosts. But Ormyrus labotus had been observed to lay its eggs in more than 65 different species of insects – many more than one or a few.
Ormyrus labotus parasitises gall wasps, which lay their eggs on plants, prompting them to form protective, swollen structures called galls around the larvae (a parasite, in a parasite!). When galls of different wasp species are formed, they take on different sizes and shapes. Some are much harder than others, some have unusual defense strategies. There are galls that are divided into chambers, secrete nectar or are bristly with fibers. Parasitoid wasps often have specialized adaptations that allow them to attack certain types of bile.
But Ormyrus labotus, it seemed, had no problem invading a series of galls: lime-green and stippled round galls, spiky yellow galls on a leaf’s leaf, and stubbly galls on a twig. “It seemed odd that one species could effectively attack all these different galls,” said Sofia Sheikh, a doctoral student at the University of Chicago who studied the wasps when she was at the University of Iowa.
It turns out that entomologists had good reasons to be suspicious. After extracting DNA samples from parasitoid wasps collected from oak trees across the country, Ms. Sheikh and colleagues from the University of Iowa revealed that Ormyrus labotus is actually a complex of at least 16 genetically distinct species that are essentially indistinguishable for the eye . Their research was published Wednesday in the journal Insect Systematics and Diversity.
The paper, the researchers note, is the latest in a series of studies that unmask supposedly generalist parasitic insect species as complexes of many species. And the scientists are sure that more of this hidden diversity lurks in insects that haven’t been studied for decades — there may be even more species of Ormyrus labotus.
These examples teach scientists to “be suspicious” of parasitic wasp species believed to be generalists, said Josephine Rodriguez, an entomologist at the University of Virginia’s College at Wise, who was not involved in the study.
The paper grew out of a larger project studying the coevolution of North American gall wasps and their parasites, said Andrew Forbes, an evolutionary biologist at the University of Iowa. “No one has looked at these groups for 50 to 100 years,” said Miles Zhang, a research entomologist at the USDA Systematic Entomology Lab, adding that much of the work on gall wasps was completed by biologist Alfred Kinsey, who is much better known for its namesake human sexuality scale.
Ms. Sheikh and Anna Ward, a graduate student in Iowa, spent several years picking galls from oak trees, searching iNaturalist, a social network of biologists and other scientists, and inviting themselves into people’s backyards. They returned the galls to the lab, placed them in separate cups in a refrigerator-sized incubator, and waited to see if the gall wasps, parasitic wasps, or both would hatch — two wasps with one stone. “It’s often more like 20 wasps in one fell swoop,” clarified Dr. Forbes. “Each gall wasp is attacked by between 10 and 25 different species of parasites.”
As the wasps hatched and chewed out of the galls, the researchers took samples of the insects’ DNA to examine the genetic variation between them. They then compared genetic results with the ecological findings, meaning which wasps were found on which types of galls on which trees. They also studied the anatomy of the insects, which were less helpful because the wasps were very similar. For example, they found that the wasps most likely represented at least 16 species. (There may have been two more, but the researchers didn’t have enough samples to be sure.)
Although the researchers did not expect Ormyrus labotus to be a single species, 16 to 18 different species came as a surprise. “Here are all these species in our small sample,” said Ms. Sheikh. “It means there’s a lot more that we haven’t captured yet.”
The paper does not describe or name any species in the complex, as such taxonomic work requires more evidence and microscopic measurements of the wasps’ body parts. And the DNA analysis looked at just a single bar-coding mitochondrial gene. But dr. Forbes hopes someone will take on the taxonomic mantle and name each of these 16 to 18 long-overlooked wasps. “This research makes it clear that we need further support to educate and fund more taxonomists,” said Dr. Rodriguez.
Distinguishing dozens of identical-looking wasps from the mud of a single species is not just a taxonomic exercise. Their extreme specializations make parasitic wasps excellent pest managers; in Hawaii, the parasitic wasp Eurytoma erythrinae has significantly reduced the populations of a gall wasp that threatened the native wiliwili tree.
According to Dr. Zhang, entomologists often focus on bees and ants — the most notable insects in the order Hymenoptera — while neglecting small parasitic wasps.
“They’re so undervalued because they’re so small,” said Dr. zhang. “But they are iridescent, with beautiful glowing eyes.”
dr. Zhang, who works out of the Smithsonian National Museum of Natural History, says the museum has at least 100 specimens labeled Ormyrus labotus. The little wasps are normally kept in drawers. But when brought into the light, their iridescent bodies will glow and look different from every angle.