Fellow Leaf Mine Enthusiasts

The other day I went out to pick some spinach for breakfast, and I noticed this fly resting on one of the leaves:

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This is a lauxaniid fly in the Minettia obscura species group, which I recognize mostly by the orange-tinted wings. I often see them resting on leaves, but they usually only let me get one imperfect photo before flying away. This one clung steadfastly to the leaf even after I picked it and continued to fill my hand with other spinach leaves. As I was walking back to the house, it wandered away from its perch and revealed that it had been sitting on this leaf mine, which was small enough to be obscured by its body:

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This is a very early mine of Pegomya hyoscyami (Anthomyiidae), another fly. The larvae would devour the entire leaf within a few days if I let them, but as long as we eat spinach regularly we’re able to stay ahead of these flies for the most part (and the occasional leaves that become too infested for us to want to eat go to the chickens instead). Anyway, the lauxaniid moved to the underside of the leaf and proceeded to probe the Pegomya eggs with its mouthparts.

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It continued to do this even as I walked inside, set down the rest of the spinach leaves in the kitchen, and placed the fly’s leaf on my desk to take these photos. (By the way, all the tiny spheres on the leaf are calcium oxalate crystals that originate from the leaf’s stomata.)

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As you can see, by the time I started taking pictures it had stepped away from the eggs a bit, but still showed no interest in abandoning the leaf. Finally, I took the leaf back outside and had to blow on the fly as hard as I could about five times before it finally decided to take off.

As I’ve mentioned previously, the larvae of some lauxaniids (including some Minettia species) are leafminers in decaying leaves on the ground. Others feed externally on decaying plant matter. I suppose this one was attracted to the compromised tissue where the Pegomya larvae had begun to mine the leaf, but it seemed odd that it was so unwilling to leave this leaf behind.

Yesterday I went for a walk in the woods and spotted one of the mystery leafminers I’ve been trying to rear for the past few yearsan unknown scathophagid fly on painted trillium (Melanthiaceae: Trillium undulatum).

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I had never encountered this phenomenon before, but just three days later, here was another lauxaniid sitting on a leaf mine! I believe it was another Minettia, though not in the obscura group.

I didn’t have my good camera/lens with me, but the fly obligingly sat there while I took several photos until I’d gotten the best shot I could with the camera I had.

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It stayed on the leaf after I picked it, departing only after I rolled the leaf up and slipped it into a rearing vial.

So what’s going on here? It’s tempting to think these flies are laying eggs on or in the leaf mines and their larvae will develop as secondary invaders in the mines, maybe after the original miners have left. For that to be the case, of course, both of these flies would have to be females, and I’m not familiar enough with these to be able to tell from the photos. Naturally, I ate the spinach leaf and destroyed whatever evidence might have been there, but I suppose I’ll hang onto the trillium leaf for a while after the scathophagid larvae exit it and see if any lauxaniid larvae appear.

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Portraits of a Sedge Muncher

I haven’t been going for many walks with a camera lately. I spend so much time viewing the world through various lenses and screens that it’s refreshing to experience it through my own bleary eyes from time to time. But the other day I spotted a Calligrapha beetle on our mulberry tree, and it was sufficiently fancy that I had to dash inside to get my camera. Once I finished with the beetle and was already outside with my big old macro lens, I figured I might as well take a quick stroll through our woods and see what else I could find.

What I found was a furry Ctenucha virginica caterpillar munching on the tip of a sedge leaf (Cyperaceae: Carex). It was just small enough to fit comfortably within the 2-cm field of view of the MP-E 65mm.

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I didn’t notice as I was taking the above photo that there are a few little green crumbs of sedge leaf on the left side of the caterpillar’s face. You can also see, in this photo and in the two below, the tiny barbs on each of its hairs, as well as the serrations on the margins of the sedge leaf that give it its rough texture. But what really caught my attention as I zoomed in was the structure of the caterpillar’s prolegs that grasped either side of the leaf.

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The curved, translucent structure, I just learned, is called the “planta,” and the tiny gripping hooks that come out of it are called “crochets” (as in crochet hooks). Virtually all butterfly and moth larvae have these hooks, even leafminers that don’t have anything that looks like legs, and this is an important feature in distinguishing them from sawfly larvae.

Ctenucha virginica, by the way, grows up to be a kind of tiger moth (Erebidae: Arctiini) called (get this) the Virginia Ctenucha. Apparently I haven’t photographed one in well over a decade, but they are distinctive day-flying moths that visit flowers, so they’re not hard to find. Here’s one sipping some Queen Anne’s lace.

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In Search of Spring Beauties

Although spring is technically already half over, it only really got started around here in the past week or so. Yesterday I saw my first spring beauties (Montiaceae: Claytonia caroliniana):

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These little wildflowers are only around for a few weeks before they disappear along with their leaves, as do trout lilies, wild leeks, Dutchman’s breeches, and squirrelcorn. It’s striking how few of the spring wildflowers host any leafminersnot just these true “ephemerals,” but even many with persistent leaves: bloodroot, wild ginger, blue cohosh, early meadow rue, starflower, and goldthread are all entirely lacking in miners.

So I was excited to find some mines on spring beauty three years ago (May 17, 2015) during a walk in Marshfield, Vermont:

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Here’s a backlit view of a different leaf, showing a larva feeding at the tip:

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A look at the undersides of the leaves revealed tiny white eggs at the beginnings of the mines:

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There are two eggs in the above photo, one of them unhatched. If you think they’re hard to spot, try finding them on a life-sized leaf! Here’s a closer view of a hatched one, next to a bit of pollen:

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They were so tiny that I failed to recognize them as eggs of Pegomya (Anthomyiidae)the genus that includes the flies that are already ovipositing in earnest on the spinach in our hoop houseand mistook them for Scaptomyza (Drosophilidae). As a result, after collecting them I didn’t provide the larvae with soil to burrow into, which is generally necessary when rearing anthomyiids. They began to pupate within two days, and although I had collected many larvae, I only ended up with one adult (on June 11):

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As discussed in my paper on leaf-mining muscoid flies that was published earlier this year*, this was a female, and a male would be needed to identify the species with certainty. I sent it to Brad Sinclair at the Canadian National Collection and he said it might be Pegomya flavifrons, but he noted that it was dark compared with the much more yellow specimens of that species in the CNC. Pegomya flavifrons normally feeds on plants in the pink family (Caryophyllaceae). Here is one I reared from mouse-ear chickweed (Cerastium fontanum) in Maine:

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Although this P. flavifrons is a darker gray, it does have a lot more yellow on its abdomen and face.

So this spring I’m hoping to find more larvae and rear some males to get a definite answer. However, I rarely encounter spring beauty where I live, and I have only seen mines on it that one time, so I’m hoping this post will inspire some of you to keep an eye out for them. If you find any larvae, please either try and raise them, or pass them along to me, or at least tell me where you found them!

* Eiseman, Charles S. 2018. New rearing records for muscoid leafminers (Diptera: Anthomyiidae, Scathophagidae) in the United States. Proceedings of the Entomological Society of Washington 120(1):25-50.

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Spring Sparkler

Happy spring! You may be wondering where I’ve been for the past few months, unless of course you’ve subscribed to the monthly leafminer book installments, in which case you know I’ve been busy putting together a 383-page illustrated introduction, complete with overviews of all of the known groups of North American leaf-mining insects and their predators and parasitoids. The moth chapter in particular was a major undertaking—it turns out that leafmining has been documented in 40 families of Lepidoptera, with one in every ten described species mining leaves for at least part of its larval development.

From here on out, I’ll mostly be adding illustrations and making minor edits to the keys and species accounts I’ve already written. Having reached this milestone, on April 1 I decided it was safe to take all of the overwintering bugs out of the fridge. Three days later, the first adult emerged: Dyseriocrania griseocapitella (Eriocraniidae), which for reasons unknown to me someone has decided to call the “Chinquapin Leaf-miner Moth.” Okay, it’s one of just two leaf-mining moths that have been specifically recorded from chinquapin (Fagaceae: Castanea pumila), but if anyone did some looking I’m sure they’d find that some of the other 15 moths known to mine Castanea leaves can also be found on that species. Larvae of D. griseocapitella are much more commonly found mining leaves of various oaks… along with at least 130 other North American insects. I do think the common name for the family Eriocraniidae, “sparkling archaic sun moths,” has a nice ring to it though.

Anyway, here is one of the mines, collected nearly a year ago, shortly after the oak leaves had opened:

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Two days after the leaves were plucked, three larvae exited their mines and I gave them a jar of soil to burrow into.

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On my rearing page I noted that after overwintering, “Because I’m worried about moths rubbing off their scales in plastic bags, when I have a baby food jar with soil containing eriocraniid larvae, I take the lid off of it and put it in an upside-down peanut butter jar.” Today when I spotted the moth in the jar, I had the presence of mind to take a picture to show what I mean:

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That dark spot at the top of the inverted jar is the moth—here’s a closer look:

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The position of the flash heads makes a big difference in the appearance of the sparkly wings.

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Although I like the second one best, the occasional purple scales in the third one are pretty nice.

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And, just so we’ve got every angle covered:

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So, it’s clear where the “sparkling” in “sparkling archaic sun moths” comes from. The “archaic” refers to Eriocraniidae being one of the most “primitive” lineages of moths. An interesting feature shared by the three most “primitive” families—Micropterigidae, Eriocraniidae, and Acanthopteroctetidae—is that the pupa has free antennae and legs as well as functional mandibles, which it uses to wriggle its way to the soil surface so that the adult can emerge. Remembering this, I hunted around a bit and was able to find the pupal exuviae poking out of the soil.

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As for the “sun” part, these moths are diurnal, as illustrated by this excerpt from an email sent to me in January by the British dipterist Michael Ackland after I sent him the first installment of the book (as thanks for all his help identifying anthomyiid flies):

The leaf-mining microlepidoptera will be very exciting with the leaf mines and adults very well photographed. My first interest in insects was when I was about 14 when I collected microlepidoptera. I recollect collecting those primitive purple moths around birch during the war (1941). It was on a golf course near Bristol and a German bomber was somewhere overhead. They tried to make daylight raids on Filton, a nearby wartime aerodrome.

Those purple moths on birch would have been Eriocrania semipurpurella, which also occurs here in Massachusetts but I’ve been unable to rear it so far. Maybe this time around…

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Pesky Parasitoids, Part 3

First, another quick update on the leafminer book. Some people have asked if there’s a way to get it without recurring monthly payments, and/or by writing a check rather than going through Patreon. At the same time, Patreon recently announced that they’re about to start adding a service fee to every pledge. So I’ve come up with some new options, which you can check out on this page (scroll past the picture of the moth to see them). Anyone who has already signed up through Patreon is welcome to switch at any time, or to stay there if you’re happy with it.

And now for a little break from leafminers…  In our surveys on Nantucket, Julia and I have started to branch out to looking for other obscure herbivorous insects rather than just gallmakers and leafminers, with the thought that we’ll eventually stop finding new galls and leaf mines. Some of the things we’ve been focusing on lately have been micro-moth larvae that fold, roll, and tie leaves. On July 30, while walking around Stump Pond, we noticed a patch of bugleweed (Lamiaceae: Lycopus uniflorus) in which many of the leaves were curled downward laterally and nibbled toward the tips. These three photos are different views of the same leaf:

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In that last photo, you can see that there’s a tube of silk within the leaf curl. Here’s a better look at one on another leaf:

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There was a caterpillar in each leaf curl, but they all zipped back into the safety of their silk tubes before I could get any photos of them. We collected several to try and rear, but within five days, braconid wasp larvae started emerging from them—all of them—and spinning cocoons. At least braconids don’t devour their hosts very thoroughly, so I have a photo of a recently abandoned corpse that gives some idea of what the caterpillars looked like.

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On August 15, an adult microgastrine braconid emerged from one of the cocoons. Note the neat circular lid it cut from the end of the cocoon when it emerged.

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There were four other cocoons, but nothing else emerged until September 5. Then, over the next week, these little cuties emerged from three of the cocoons:

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Unlike the braconid, they emerged through ragged holes in the cocoons:

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These wasps belong to a species of Perilampus (Perilampidae), and they are obligate hyperparasitoids with an unusual way of locating their hosts. Instead of seeking out a suitable host larva in which to oviposit, the female lays her eggs on leaves. It is then up to the newly hatched larvae to wander in search of a parasitized caterpillar, burrow into it, locate the parasitoid larva (which might be a wasp or a tachinid fly), and burrow into that. The Perilampus larvae in my bugleweed caterpillars bided their time while the braconid larvae finished feeding and popped out and spun their cocoons; then they got around to devouring the braconid larvae or pupae, at which point they conveniently had ready-made cocoons in which to pupate. It all seems very improbable, but I guess it works for them!

Edit, 1/23/2018: I sent these specimens to perilampid specialist Chris Darling, and he says:

I have had a look at your specimens and they fit nicely into my concept of Perilampus platigaster Say, 1836.  But yours is the best rearing record we have for this species.  Specimens have been reared from the grape leaf roller, Desmia funeralis, but the details of the association, and the primary parasitoid, were not available or not recorded.  And your rearing information agrees very well with the numerous host records that Dan Janzen has for this species group from Costa Rica.

Your account of the biology of Perilampus [above] is quite good.  But I would note that not all species are hypers.  And as far as we know the planidia do not search for parasitized caterpillars — but rather the planidia enter the caterpillars before they are parasitized.  And they only develop if the caterpillar is subsequently parasitized, which makes the life history all that more bizarre.  Planidia show up in genitalia preparations of moths occasionally, so they entered the caterpillar and were marooned when the caterpillar was not parasitized and subsequently metamorphosed into an adult!

And I am sure you will keep an eye out for Perilampus next summer!  Perhaps you will find them ovipositing on bugleweed near leaf rolls.  Sadly, they do not appear to parasitize  leafminers!  Almost certainly the mines provide protection against the tiny marauding planidia.

Here is an example of a planidium that Terry Harrison found while dissecting a moth.

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Pesky Parasitoids, Part 2

Back in August I gave a talk and co-led a walk at an event in southern Ohio called “On the Trail of E. Lucy Braun”, a celebration of the life and work of a renowned Ohio botanist and conservationist. I was there, of course, to make sure Lucy’s sister Annette was properly represented. The walk took place at Lynx Prairie, a site the Braun sisters visited regularly. On August 25, while we were scouting for the walk, Julia spotted a single mine of a Brachys larva (Buprestidae) in a leaf of hophornbeam (Betulaceae: Ostrya virginiana).

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This beetle genus is primarily associated with oaks, apart from the recently described Brachys howdeni on trailing arbutus (Ericaceae: Epigaea repens). Any larvae found on other host plants are of particular interest as Henry Hespenheide works to  revise this confusing genus, and hophornbeam was a new host record as far as I knew. So I kept a close watch on this larva after we collected it, struggling to decide whether it was better to preserve it for DNA barcoding or attempt to rear it to an adult (which was by no means guaranteed to succeed, and would involve waiting until spring).

On September 1, I was dismayed to discover an ectoparasitoid attached to the larva:

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So the decision was made for me. As we saw in my previous post, I didn’t have much time to lose before there was nothing left of the larva. I tore open the mine, giving me a better view of a parasitoid larva than I normally get to see…

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…and then I wrested the parasitoid away from what was left of the beetle larva, plunking the latter in a vial of ethanol so I could try and get a DNA barcode from it later. I offered the wasp larva a Brachys larva from another host plant, but it showed no interest in it. Instead it wandered the rearing vial forlornly for several days, finally settling down to pupate on September 5. My pictures of the pupa aren’t great because the first was taken through the wall of the vial, and the second was taken at an awkward angle looking down into the vial.

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As you can see, this larva deposited liquid meconium rather than the apparently solid pile left by the Stigmella parasitoid. Between ten and twelve days later, the adult emerged (while I was away at the Berkshire BioBlitz, so I didn’t get to see it alive).

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I suspect she’s another Pnigalio (Eulophidae) of some sort, but time will tell.

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Pesky Parasitoids

A big “thank you” to my first 13 patrons! I’m almost done writing the main introductory chapter that I’ve been putting off dealing with for a few years now, and soon I’ll get to work trying to put together a reasonable summary of the various groups of wasps that parasitize leafminers… which reminded me of a couple of wasps I got to watch develop this year, so I thought I’d share the photos here.

On September 16 Julia and I participated in this year’s Berkshire BioBlitz in Great Barrington, MA, naturally focusing on the galls and leaf mines that no one else was going to look at. When we encountered some mines of nepticulid moths on black birch (Betula lenta) leaves, we were compelled to collect them and try to rear them out, because there is a bewildering array of similar mines on birches that still need some sorting out. As I was taking a backlit photograph of each mine that still contained a larva, I saw that this one had a problem:

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Namely, it had an ectoparasitoid chomping on its back.

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The following night, all that remained of the moth larva were its head capsule and (please correct me if I’m wrong) Malpighian tubules, and the wasp larva had begun to wander back down the mine channel.

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It continued to work its way back until the next morning.

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A day later, it had backed up just a little bit (you can faintly see its pointy posterior end crossing the moth larva’s frass line in the photo below), and its gut contents had visibly consolidated.

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Another day later, it had finally pupated, depositing its shed skin and meconium (all of the accumulated waste products from its life as a larva) in a heap where the tip of its abdomen had been the day before.

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Eight days after that, the adult wasp had chewed its way out of the leaf, leaving its pupal exuviae behind.

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This is a eulophid wasp, very similar to this one that Christer Hansson identified as Pnigalio flavipes. That was before he examined more of my reared eulophids and decided that the whole genus Pnigalio is in serious need of revision because, for instance, males and females that clearly belong to the same species key out to different species using the existing keys.

I’ll save the other wasp rearing series for another day!

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