Strange berry-like form holds a hidden world

When I first noticed the large, red form in late July, I thought I’d found some kind of mutant berry. About 1½ inches long and three-quarters of an inch wide at its thickest point, the purplish-red “fruit” was faintly pear-shaped, with bristly, almost thorny, hairs covering its rough skin. Because it grew near some red raspberry plants, I wondered if it might somehow be related to those berries. Or maybe it was a deformed rose hip. Of course, rose bushes were also nearby.

Whatever it was, the object seemed to grow directly from the plant’s main stem, no more than an inch or two above the ground. And the stem ended just above the bulging shape.

Curious to know more, I pulled out my iPhone, went to its iNaturalist app, and used the fruit’s image to seek its identity. What came up was Diplolepis polita, the “spiny leaf gall wasp. A “gall” is a deformity caused by the eggs or larval forms of insects “invading” a plant, most commonly a leaf. The suggested ID also indicated that a wasp was responsible for this particular gall.

I vowed to learn more. But before I could do an online search, I heard back from two iNaturalist “identifiers.” Both suggested that a wasp named Diastrophus turgidus had produced “my” gall.

It turned out that one of the two, a fellow named Charles, is a Ph.D. candidate studying members of the Diastrophus genus. He wondered if I’d “be open to collecting and sending the gall” to him in the hope that he might “rear wasps” from it.

I expressed my willingness to do so and asked Charles if he had any special instructions on how to best wrap/preserve the gall for mailing and further indicated my desire to know how the gall is formed. That began a series of exchanges that have now stretched across several weeks.

My package safely reached Charles on August 9, and after a couple of gentle reminders, he sent me some general information about Diastrophus turgidus and its gall.

A good starting point would be to share a definition of “gall.” Charles simply describes it as a “tumor-like growth” on a plant (a description he apparently pulled from the Current Biology article). A more detailed description I found online is this: “An abnormal swelling of plant tissue, caused by injury or by parasitic organisms such as insects, mites, nematodes, and bacteria.”

Next, Diastrophus is a genus of gall wasps that are part of the larger Cynipidae family. D. turgidus is one of least eight species known to occur within that genus and reportedly was first identified in 1870 by Homer Franklin Bassett, who described the gall as “an abrupt swelling involving the whole circumference of the stalk.” (Taking things back even farther in time, Current Biology notes that the study of gall wasps in general included the work of “pioneering 19th century female naturalist Mary Treat.” Need I add that it’s refreshing to see groundbreaking women being acknowledged this way?)

It’s almost a certainty that other species have not yet been identified, because much remains unknown about galls and the organisms that form them.

Are you with me so far? The best is yet to come!

The wasps that create the gall I happened upon in Ruth Arcand Park target only Rubus idaeus strigosus, better known to us ordinary folks as the American red raspberry. It was, therefore, no coincidence that I found the gall near several other raspberry bushes. Nor was it a coincidence that the gall formed on the plant’s main stem because that’s where these particular gall wasps lay their eggs.

As Charles explains, the cycle starts with an adult female wasp mating with an adult male. The female then searches for a suitable host plant — a red raspberry—and injects or oviposits her eggs into the stem tissue. (Apparently, multiple wasps may deposit eggs on the same stem.)

That egg laying begins the gall’s formation, a three-stage process that apparently is stimulated by the adult wasp’s venom, in combination with salivary secretions from the larval forms produced by its eggs.

I won’t go into the details of that process here for several reasons. First, the scientific terminology is hard to follow—and even harder to translate into ordinary language for a forum like this one. Second, as Charles admits, “The exact mechanisms responsible for and behind the development and growth of the galls is still being uncovered.” Or as the authors of the Current Biology article put it, “We still know little about how galls are induced.”

In the end, the interaction of wasp and raspberry stem produces a softer, nourishing interior with enough room for up to several dozen chambers in which the larvae can grow and thrive; and a harder, thorny, protective outer layer.

Researchers say the gall benefits the wasp’s larval and pupa stages in at least three ways: the host plant provides nutritious “food”; the gall offers a “stable environment” while protecting the developing wasps from harsh external conditions, for instance, extreme weather; and it helps defend them from predators.

What’s also rather remarkable is that the gall forms an entire ecosystem of life forms. In fact, gall wasps are considered “ecosystem engineers” in that they “modify the environment” in a way that enhances species diversity and richness. This is possible because the gall does not provide their wasp creators full protection. Eventually, an assortment of other organisms may inhabit the gall, including a wide array of parasites and predators that may “attack and consume” at least some of the wasps in their larval or pupating forms.

There’s lots more to this story, including much that’s yet to be discovered by researchers. What strikes me the most is the complexity, diversity, and mystery that this strange-looking gall — and many other galls on other plants — holds within it.

It’s so easy to miss or ignore the many insects that inhabit what we humans imagine to be “ordinary” woodlands; to overlook or turn away from the abundant blemishes — many of them galls of various kind — that adorn local plants; and to give little or no thought to the many complex natural processes going on around us all the time.

Sometimes it takes a mutant-like form to get a guy’s attention and lead him into a largely hidden and rather extraordinary world, yet another of the many small but marvelous wonders with which (or with whom) we share this miracle of a planet.

What I’ve learned seems wondrous enough that I’ve asked myself these questions: would I have so casually and willingly cut off and mailed that gall if I’d known then what I know now? Or would I have left the gall and its wasps and other life forms to their own destiny in the woods, perhaps checking now and then to see how that strange entity might change over time and, if lucky, perhaps even see adult wasps emerge from the hiding place they once helped to create as larval forms?

Anchorage nature writer Bill Sherwonit is a widely published essayist and the author of more than a dozen books, including “Living with Wildness: An Alaskan Odyssey” and “Animal Stories: Encounters with Alaska’s Wildlife.” Readers wishing to send comments or questions directly to Bill may do so at akgriz@hotmail.com.