Carrot Stem Dwellers

Carrot (Apiaceae: Daucus carota) is native to Europe but widely cultivated and has become a ubiquitous weed in North America (also known as Queen Anne’s lace), so you’d think we’d have a pretty good handle on what bugs eat it by now. You’d be wrong.

Black swallowtail caterpillars (Papilionidae: Papilio polyxenes) are well known to feed on a variety of native and nonnative plants in the parsley family, and I often see them munching away on wild carrot leaves in my yard…

…but I’ve also come across a surprising number of other carrot-feeding insects in my yard that don’t seem to have been documented before. In 2017 I reared two adults of the micro-moth Epermenia albapunctella (Epermeniidae) from larvae that initially made tiny mines in the leaves, later feeding externally from little webs. This species was not previously known to feed on carrot, or to mine leaves. When I did my intensive year-long cataloguing of leaf and stem miners in my yard in 2020, it was #40:

And then #179 was a stem-mining fly; the relevant section of that post is repeated here:

[Begin quote]

Leaf (stem) miner #179: Ophiomyia sp. (Agromyzidae), on wild carrot / Queen Anne’s lace (Apiaceae: Daucus carota). I was excited to find this mine on the evening of September 5:

No Ophiomyia is known to feed on wild carrot, but Julia and I found a bunch of similar mines on an isolated clump at Black Rock Forest in New York late last August while conducting our survey for leaf-mining moths there. The puparia in those mines were all black, and only eulophid wasps emerged from them. The puparium in the above mine (visible as a bulge along the upper margin of the stem) was whitish; unfortunately it turned out to be empty already.

In this close-up, the pair of little black anterior spiracles of the puparium are visible poking through the stem epidermis at far left, and there is a longitudinal opening associated with those—along with a more conspicuous transverse slit to the right of them—indicating that the fly has already emerged. I spent a good chunk of yesterday pulling up wild carrot stems around the yard, and I found six stems with intact puparia (plus one more empty one, and one or two that seemed to still have larvae in them). To give a sense of how sparsely distributed these mines are, this is how many stems I had to inspect to find a half dozen of them (note Brenda in the background; she followed me around for most of the time that I was pulling them up, and was often literally underfoot):

All of the mines were confined between two nodes in the stem as in the example shown above. John van der Linden has observed similarly constrained stem mines (both agromyzid and Marmara) on Ageratina altissima, Polymnia canadensis, and Veronicastrum virginicum in Iowa.

[End quote]

That’s where I left the story, so I’ll pick it up from there. At the beginning of October 2020, this braconid wasp (subfamily Opiinae) emerged from one of the six puparia I’d collected on September 6.

When I looked at the puparia under magnification to figure out which one it had come from, I discovered that two of them had exit holes (one of them had evidently only looked intact to the naked eye), so now I just had four left. I assume this braconid came from the puparium with the more conspicuous hole:

On October 16 I put all of my rearing projects into the fridge for the winter; I took them back out on March 1 of last year. On March 29, another parasitoid emerged: this time, a pteromalid in the genus Herbertia.

Nothing ever emerged from the remaining three puparia. So naturally I was watching closely for the first mines to appear last summer, and I spotted the first one on August 4. This prompted me to spend the next couple of hours pulling up every wild carrot stem in the section of my front yard bounded by the driveway, upper vegetable garden, and shed, yielding a total of four mines: three in stems, each of which already contained a greenish-white puparium like the one toward the right side of this photo…

…and one mine in a leaf stalk, in which a larva was still feeding (at right):

I suspect that in this species a black puparium is an indication that a parasitoid will emerge, and a whitish puparium means there is some hope of a fly emerging.

When I went to pull up the last stem before quitting for the day, I was shocked to discover that not only did it have two mines in it, but they were Marmara (Gracillariidae) instead of Ophiomyia.

There are no previous records of Marmara from wild carrot, or from anything else in the parsley family for that matter. But the continuous central frass line in these mines told me at once they were Marmara; in Ophiomyia stem mines the frass is much less conspicuous, and it is deposited either in widely spaced grains or in little strips that alternate from side to side. One of the Marmara larvae is visible to the right in the above photo, but it’s a little hard to make out. Here’s a close-up of the other larva, with its head pointing toward the upper left corner:

Needless to say, I stuck this stem in a ziplock bag to see if I could rear the larvae to adult moths.

On August 6, I pulled up all the wild carrot stems from another section of the yard, found a few more puparia, and three days later an adult Ophiomyia emerged from one of them! For some reason it was already dead when I found it, even though I’d been checking the rearing vial regularly.

It’s a female, which means that when Owen Lonsdale gets around to examining it, all he’ll be able to tell me is that it’s some kind of Ophiomyia. Without male genitalia, I’m no closer to getting a name on this fly than I was when I just had parasitoid wasps.

On August 14, another fly emerged! …Another already-dead female.

On August 13, a braconid emerged—this time belonging to the subfamily Alysiinae.

Alysiine braconids have weird, outward-facing mandibles that they use to pry open the host fly’s puparium along an existing line of weakness at the anterior end, so that the emerging wasp leaves an opening similar to the one an emerging fly would leave, as opposed to the ragged-edged hole an opiine braconid chews.

On August 12 I stripped yet another section of my yard of its wild carrot stems, found a few more puparia, and two days later a fly emerged from one of them! …Another sorry-looking female.

Another alysiine braconid from the August 6 collection emerged that day. On the 15th, the fly that I had collected as a petiole-mining larva on August 4 emerged as an adult… another lousy female.

It’s still a mystery to me how one fly after another managed to make itself so dead in such a short amount of time. On August 17, another adult emerged—from another carrot-pulling session on August 10 that I guess I neglected to mention—and this one was alive!

…But it was just another female. How many females do I have to rear before we decide that this must be a parthenogenetic species, and there never will be any males? I don’t know, but more than five.

On August 21, a pteromalid emerged from one of the August 6 puparia; this time a miscogastrine rather than a herbertiine.

On August 22, another alysiine braconid.

On August 25, one of the Marmara adults emerged! It had rubbed some of its wing scales off in the bag, but that was okay; as with the flies, distinguishing them is all about the male genitalia.

Two days later, the other Marmara! It was a little drunk for some reason and kept flipping on its back, so its wings were even more rubbed than the first one’s, but no matter; they both had abdomens, and that’s what counts.

I pretty thoroughly inspected the carrot stem from which they had emerged and couldn’t find either moth’s cocoon. Some Marmara species exit their mines to spin cocoons, and others cut out a little flap in the stem epidermis at the end of the mine and spin their cocoon under that. I was too busy with fieldwork to keep looking right then, but I wanted to know what this species does, so I kept the stem in the bag to examine again when I had more time.

On September 1, another miscogastrine pteromalid emerged from one of the Ophiomyia puparia.

On September 9, this little dark-winged fungus gnat (Sciaridae) appeared in the bag with the Marmara-mined stem.

I had continued to pull up wild carrot stems from my yard throughout August. An Ophiomyia puparium I collected during the August 21 session produced this eulophid wasp (subfamily Entedoninae) on September 6:

On October 11, I looked over at that bag with the Marmara-mined stem in it, and there were several more of those dark-winged fungus gnats in it. There was also a weevil:

I had noticed some powdery frass coming out of a hole in that stem a while back, so I knew there was some kind of larva boring inside it, and it didn’t come as a complete surprise to see the weevil in the bag. With a quick internet search, I learned that there is a species that looks sort of like this called the carrot weevil (Curculionidae: Listronotus oregonensis); the sources I found mentioned it feeding on the root, but I figured the focus was on that because that’s the part people care about, and it seemed plausible that the same species could also bore in carrot stems.

I surmised that the fungus gnats must have been developing inside the weevil’s tunnel, feeding as larvae on its frass and the damaged/dying plant tissue. By November 5, a total of 60 of them had emerged. Sixty!

I sent the weevil to Bob Anderson at the Canadian Museum of Nature, along with some others I’d accumulated over the past few years, and he told me, “The mystery weevil from Daucus is a Listronotus but I don’t think it’s oregonesis as it’s a bit small for that species.” No comment on what he did think it was.

I sent the fungus gnats to Kai Heller in Germany, and he reported: “All individuals belong without doubt to the same species, namely Bradysia impatiens. This is the common greenhouse midge, which has a worldwide distribution. . . Unfortunately this is not a very interesting record.”

I sent the flies to Owen Lonsdale, who hasn’t had a chance to look at them yet, but we already know what he’ll say, since no males ever emerged.

Probably no one will ever look at the wasps.

As for the Marmara specimens, they came along at an inopportune time, when Julia and I were both impossibly busy, and they were part of a batch of moths that were left on spreading boards for several weeks in a box that had no mothballs left in it. Some time in the fall, we discovered that booklice had eaten most of the abdomens in the box, and the Marmaras were not spared. In fact, one of them is now nothing more than a thorax on a pin.

I’m reminded of this tragedy every day, because back in June, a booklouse appeared in my camera’s viewfinder:

It hung out in the upper left corner there for a few days, then it disappeared for a week or so, but then it reappeared, changing position a few times, until it finally died right near the middle of the field of view, where it still is to this day.

On the plus side, just a few more months until more wild carrot stems start popping up all over my yard; maybe it will all go better this time around!