Is That a Gall Wasp? Now You Can Find Out
By Leslie Mertz. Ph.D.
People are intrigued by insect galls, those strange, often colorful, and oddly shaped outgrowths that decorate tree limbs and plant leaves. While scientists know that a large group of tiny wasps are responsible for many such galls, only a handful of experts in the entire world are actually able to identify the diversity of gall wasps and other members of the broader superfamily Cynipoidea.
That is about to change, however, as a new key to the gall wasps has now been published in the journal Insect Systematics and Diversity and promises to help ecologists, extension agents, and others determine which wasps are affecting—and in some cases helping to protect—the planet’s forests, farms, and fields.
“It’s easy to recognize an unknown hymenopteran (the order Hymenoptera includes such insects as bees, wasps, and ants) as being a member of the superfamily Cynipoidea, but it’s almost impossible to figure out what family, subfamily, or tribe it belongs to, so we really needed a key to these higher classifications within the superfamily,” says cynipoid expert Matthew Buffington, Ph.D., a research entomologist with the Systematic Entomology Laboratory at the U.S. Department of Agriculture-Agricultural Research Service in Washington, DC. The higher classifications are important because they reveal basic shared information about biology and natural history, and they help users track down pertinent scientific research already done on those groups.
Buffington and fellow cynipoid experts Mattias Forshage, Ph.D., of the Swedish Royal Museum of Natural History, and Johan Liljeblad, PhD., of the Swedish University of Agricultural Sciences, decided in 2012 to build a key to the superfamily, which encompasses more than 3,000 known species and probably at least another 20,000 yet-to-be-identified species. For the three researchers, who were co-teaching a comprehensive Hymenoptera Course in Sweden, that meant developing a series of paired statements, or “couplets” based on physical appearance, such that a user can zero in on an identification by selecting which statement in each couplet best fits a given specimen.
Buffington, Forshage, and Liljeblad got to work on the key by tracking down and distilling the best and most accurate descriptive information from more than 150 years’ worth of scientific articles, and they blended it with their own decades of experience in cynipoid taxonomy. From there, they looked for delineating characteristics and began carefully writing the couplets so they could avoid the problems that often plague keys, such as couplets with conflicting characters, confusing terminology, vague descriptions, and few or poorly done illustrations.
In addition, Buffington added photos—and lots of them—to help users compare features of their specimens to those noted in the couplets. “I wanted to have images that were as close to what a scientist, a student, an ecologist, or whoever would see if they were looking through a microscope,” he says. The three researchers also consulted two other experts, Chang-Ti Tang, Ph.D., of George Washington University and Simon van Noort of the Iziko South African Museum, to ensure the couplets were clear, and then asked their Hymenoptera Course students to try it out. “I wanted to find typos, of course, but mostly I wanted to know whether they can see the characters in a couplet, whether that character makes any sense, [and] how to phrase it best. So, since 2012, I have relied on students to use the key to find the shortcomings, and boy did they,” Buffington says, estimating that 200 students have reviewed the key over the years. “It has to be the most proofed key ever!”
Now that the key is published, Buffington is especially excited about its prospects for extension entomologists. By being able to identify cynipoids, they can not only find scientific studies and additional material about the wasps but also employ that information to help farmers, foresters, and other stakeholders understand the role of the wasps in the ecosystem.
As an example, he pointed to the eucoiline wasps, some of which can potentially serve as biocontrol agents to battle an increasingly troublesome fruit fly known as spotted-wing drosophila (SWD, Drosophila suzukii). The fruit fly lays its eggs in blueberries, raspberries, and other soft fruits, which soon fills the fruits with maggots. “A eucoiline wasp will probe a berry with her ovipositor, find an SWD maggot, and lay her eggs inside of it,” he says. Once the eggs hatch, the young begin feeding on the maggot while also suppressing its defensive immune system. The maggot soon dies, but the wasp continues its development and eventually emerges from the berry as an adult and heads off to parasitize another SWD. Buffington is currently working with global scientists to employ eucoiline wasps as a pesticide-free way to combat SWD.
Other interesting cynipoids are those in the family Cynipidae, which cause galls in oak trees. Besides causing the tree to make a protective gall, the larva inside actually exploits part of the oak’s genome and convinces the tree’s biochemical machinery to deliver select nutrients to the gall. “It’s like room service,” Buffington says. “We don’t know how the larva does it, but if we could figure that out, imagine what we could do with soybeans or corn (to make it more nutritious). It’s definitely worth paying attention to these wasps.”
The key now helps to make this kind of work possible, Buffington says. “Until this point, if you weren’t an expert or had a really good friend who was an expert, it was a very difficult group to jump into. Now, we have a rich, illustrated key that is very easy to use and, as a result, makes the entry into the research of cynipoids approachable.” He adds, “Just think of all the cool things that we can now learn by knowing how to identify these wasps.”
Insect Systematics and Diversity
Leslie Mertz, Ph.D., writes about science and runs an educational insect-identification website, www.knowyourinsects.org. She resides in northern Michigan.