Life in a Wingstem Stem

On May 8 last year, Julia and I visited her family’s land in Hocking County, Ohio (which we’ll be doing again today, as it happens), and for whatever reason, a little clump of dead wingstem (Asteraceae: Verbesina alternifolia) stems from the previous season caught my eye. I’m always amazed by all the things John van der Linden is able to find living inside of plant stems when there is little or no external evidence, and occasionally I’m moved to split a stem open at random and see what there is to see. So I got out my trusty Swedish army knife, started splitting one of these wingstem stems open, and behold! Something had been tunneling in the pith.

A little more splitting turned up what I was hoping to find: puparia of a Melanagromyza species; one of the so-called “leafminer flies” (Agromyzidae) that is a stem borer instead of a leafminer.

But the fly larvae hadn’t been the only things tunneling in there. As Julia and I split open additional stems, we also found several larvae and pupae that I thought might be Mordellidae: “tumbling flower beetles.”

Naturally, we collected the chunks of stem containing these immature insects in vials to see what they would turn into. The first thing to emerge, on May 18, was this gall midge (Cecidomyiidae):

This was not unexpected; the second Melanagromyza puparium shown above was at the edge of a slight swelling in the stem that I had thought might be a midge gall. Ray Gagné has confirmed that this midge is Neolasioptera imprimata, a species he had described just two years earlier. Here’s a better look at the gall:

Just to the right of the center of the above photo, the midge’s pupal skin can be seen poking out of the gall. A closer view:

Beginning two days later, 22 platygastrid wasps emerged from the same gall—and I only collected half of the gall, so there were probably even more midges and wasps in the other half. Jessica Awad tells me these wasps belong to the genus Platygaster, and that a species ID is unlikely to be possible anytime soon given the current state of knowledge of this genus. All platygastrid wasps (as the family is currently circumscribed) are parasitoids of gall midges.

Also on May 20, an adult mordellid beetle appeared, proving my hunch right. As far as I can tell, there is no one who studies these beetles or knows how to identify them, but this one is now in the Canadian National Collection if anyone wants to have a look at it.

On June 13, two more wasps emerged. One was a braconid parasitoid of the mordellid beetles, which Gideon Pisanty identified (based on photos I posted on iNaturalist) as a member of the tribe Brachistini (Brachistinae).

The other was this figitid wasp, which I recently sent to Matt Buffington along with 50 or so others I’ve accumulated over the past few years, and he hasn’t had a chance to look at it yet. It emerged from one of the Melanagromyza puparia.

Something dark developed inside the other Melanagromyza puparium, but nothing ever emerged from it.

According to Spencer & Steyskal (1986), the only stem-boring Melanagromyza known from wingstem (or any other Verbesina species) is M. verbesinae, which Owen Lonsdale synonymized last year with M. vernoniana—a species that, based on the specimens Owen examined, feeds on other Asteraceae including ironweed (Vernonia), sneezeweed (Helenium), sunflower, and Jerusalem artichoke (Helianthus). Spencer & Steyskal described the puparium of M. verbesinae (the holotype of which was collected in Ohio) as “straw colored, posterior spiracular plates heavily chitinized, closely adjoining, only narrowly divided, each with ellipse of about 12 bulbs around strong central horn.” This seems to fit what I found, so I’ll choose to believe that the flies I failed to rear were M. vernoniana and not something new and exciting that I need to try to find again today.

For more on the fascinating world of stem-dwelling insects, about which I know very little, check out this document John van der Linden recently put together summarizing all the agromyzid flies he’s found in this microhabitat. And you can learn about the other flies, moths, beetles, etc. he’s found living in stems by perusing his photos on BugGuide.