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!

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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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Announcements!

I have a few bits of news I’d like to share with you all:

First, I will be teaching a week-long workshop, Tracks & Sign of Insects and Other Invertebrates, at the Eagle Hill Institute in Maine next summer (July 29 to August 4).

Second, if that goes well, I will teach another course there devoted entirely to leafminers in summer 2019.

Third, a first edition of my leafminer book will be available just in time for that course!

I’ve decided to self-publish it in electronic form, in a series of 18 monthly installments beginning one month from today. There are a few reasons for this, which you can read about on my brand new Patreon page here. For those of you who are unfamiliar with it, Patreon is a crowdfunding website that allows you to support writers, artists, etc. by making monthly donations of whatever amount you choose. There are different rewards for donations that reach various thresholds. In my case, you get what amounts to a subscription to my big book of leafminers (we’re talking 1000+ pages before any illustrations are added) for just a few dollars a month, and if you feel like contributing something more towards my ongoing natural history work, there are “thank you” gifts including 8 x 10 prints, leafminer calendars, opportunities to join me in the field for a day, and (if you really want to go nuts) getting a species named after you!

I hope you’ll check it out. For a point of reference, I pay WordPress $2.50 per month so that no one has to see annoying and distracting ads on this blog. If all of my subscribers decided to chip in just that much, that would be enough for me to devote all of my time to solving and writing about natural history mysteries (I currently do this entirely in my spare time, which explains the sometimes long intervals between blog posts).

Okay, enough of that! More blog posts coming soon.

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Another Day, Another New Species

Five years ago this month, Julia and I were nearing the end of our first (and longest) trip around the US in search of leafminers. Walking up a desert wash near Tucson, Arizona, we encountered a leguminous shrub that was later determined to be “rosary babybonnets,” Coursetia glandulosa (Fabaceae).

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A number of the leaflets had small, “underside tentiform” mines…

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…which we collected in vials. Within a couple of weeks, about 20 adult moths had emerged.

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If this all sounds or looks familiar, it’s because I wrote about it nearly four years ago when I was trying to determine what the host plant was. As I mentioned then, I had initially thought this moth would be a species of Macrosaccus because that’s the genus that typically forms underside tentiform mines on legumes, but after I looked at the known species in that genus, I wasn’t so sure.

For instance, here is an adult of Macrosaccus morrisella, which I reared from hog-peanut (Amphicarpaea bracteata):

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Here’s Macrosaccus robiniella, from black locust (Robinia pseudoacacia; one wing is a little messed up, but you get the idea):

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And here’s Macrosaccus uhlerella, from false indigo bush (Amorpha fruticosa):

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All are basically solid orange with bold white markings and varying amounts of black—including a distinct black apical dot—whereas the Arizona moths were white peppered with black, with a little orange here and there. In April 2014, Julia and I visited Dave Wagner at his office in Connecticut, and after taking a quick look at one of the specimens he said it looked like a new genus. He boxed them up right then and there and sent them off to Don Davis, along with a few other interesting moths we had brought.

This spring, I sent Don some unrelated specimens, which after two months had somehow not made it to his office at the Smithsonian. When I asked one day if they had arrived yet, he searched around and found the specimens Dave had sent over three years earlier. Having just described my first moth with Don, I suggested that we do this one too. The genus wasn’t immediately clear to him, even after dissecting one, but ultimately the genitalia and wing venation indicated that Macrosaccus was a good fit after all. So we named it M. coursetiae, and the paper describing it was just published today*.

Here’s another adult of Macrosaccus coursetiae, which happens to be resting on an aborted leaf mine (tentiform mines start out flat and only visible on one leaf surface):

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* Eiseman, Charles S. and Donald R. Davis. 2017. A new species of Macrosaccus (Lepidoptera: Gracillariidae: Lithocolletinae) from Arizona, USA. Zootaxa 4358 (2): 385–392.

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The Endless Diversity of Tiny Wasps, Continued

A couple of months ago I gave a sneak preview of some new species I found during the 2016 Berkshire BioBlitz on Mt. Greylock. One of them now officially has a name, thanks to a paper that was just published today*.

Platygaster vaccinii

Platygaster vaccinii (Platygastridae) is so named because it was reared from a gall on lowbush blueberry, Vaccinium angustifolium. I mentioned this gall in my original post about the BioBlitz, which included photos of a torymid wasp ovipositing into one of the galls.

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The larva of the midge that causes the gall is bright orange when mature, and it drops to the ground to burrow and pupate. It probably overwinters before the adult emerges.

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One of the larvae that emerged from the galls I collected died before I had a chance to put it in a jar of soil, so I sent it to Ray Gagné to examine. He told me he was filing it under Putoniella at the Smithsonian, since it most closely resembled this genus, but said it could be something else. He had never heard of a gall like this on blueberry. I have since found a few similar galls on highbush blueberry (Vaccinium corymbosum) and huckleberry (Gaylussacia frondosa), but so far this single parasitoid wasp is the only thing I’ve managed to rear from them. It emerged this spring, nearly a year after I collected the gall in June 2016.

The new paper describes another new Platygaster species reared from another unidentified and previously unknown midge gall. The host plant is goat’s rue, Tephrosia virginiana, so naturally the wasp is P. tephrosiae. The galls are common on Nantucket, and like the blueberry galls they consist of simple leaf folds.

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Here’s what the (probably immature) larva looks like; Ray was only able to identify it to the supertribe Lasiopteridi:

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As with the blueberry species, this one burrows into the ground when mature. My first attempt to rear it was a complete failure. Last July I got another two larvae from two more galls, and what emerged this spring were two platygastrids. As luck would have it, there was a female (which is what is needed to identify or describe a platygastrid)…

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…as well as a male, which got to be the paratype.

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I had sent these wasps to Peter Neerup Buhl along with a few others, all of which proved to be something interesting. A series of three females and four males from Nantucket were determined to be Trichacis virginiensis, a species described in 1893 but never before reared.

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They came from galls on Virginia creeper (Parthenocissus quinquefolia) caused by the midge Dasineura parthenocissi. I also managed to rear a number of adult midges.

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The other wasps (all of these are between 1 and 1.5 mm long, by the way) were several Mike Palmer had reared from midge galls in Oklahoma. Three that he reared from these same Virginia creeper galls were determined to be Platygaster munita, a species common in Europe but new to North America. Four additional specimens that he reared from galls on wild licorice (Galium circaezans) and horseweed (Conyza canadensis) all turned out to be Metanopedias eupatorii, a species Peter had described just six years ago from Trinidad!

Oh, I almost forgot, I also reared some specimens of Platygaster rubi from blackberry galls of Neolasioptera farinosa that I collected in my backyard. This was already a known host association, which seems to be a rarer thing to come across than a new species, as far as I can tell.

* Buhl, Peter N. and Charles S. Eiseman. 2017. Host records of five species of Platygastrinae (Hymenoptera, Platygastroidea: Platygastridae) from the United States, with the description of two new species of Platygaster. International Journal of Environmental Studies (abstract)

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The 2018 Leafminer Season Has Begun!

Today on a short walk in the woods behind my house, I found some leaf mines like these on bristly/swamp dewberry (Rubus hispidus):

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A closer look at the one in the upper left corner of the above photo:

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I first noticed mines like this several Novembers ago, and although there were larvae inside they seemed to have frozen to death, and I assumed they were the result of females of Metallus rohweri, the common sawfly miner of blackberry and dewberry, laying eggs a little too late in the season for their offspring to complete development. However, in early April of 2014, the author of this blog (Dana) wrote to me about larvae he had just found feeding in similar mines in Pennsylvania, while there was still ice on the nearby vernal pool, and wondered if he might be “on to something a bit unusual”. I mentioned my previous observation, and said “I don’t know if they can actually overwinter in the mines. Probably more likely these are offspring of adults that emerged from pupal cells in the ground a week or two ago.” As far as was known, all leaf-mining sawflies overwinter as prepupae in the ground.

He replied, “Interestingly, I had concluded these larvae overwintered in the mines.” He showed me a photo of some distinctly two-toned mines, and said, “My thoughts were that the whitish areas around the leaf edges are mines from last fall, and this spring those mines were expanded into the the rest of the leaf. This photo was taken 4/10/13… isn’t that rather fast leaf-mining for early April?  I think those mines were occupied.  If so, the sawflies were ahead of the Wood Frogs…”

I agreed that he seemed to be onto something. The following January, when the temperature was well below freezing, he wrote back with photos of occupied mines he had just dug out of the snow, and said that the larvae were feeding within a few hours of having been brought indoors. In May, he wrote again to report that he had succeeded in rearing an adult. When he showed it to me, and later when I examined the specimen, I couldn’t reconcile it with either Metallus rohweri or the raspberry leafminer, M. capitalis. It was oddly pale, like this one…

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…in contrast with M. rohweri…

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…and M. capitalis, both of which have dark abdomens.

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I passed the specimen along to Dave Smith, and after some deliberation, he reported that it was Metallus ochreus, a species he had described in 1988. It was known only from adults caught in Virginia and Maryland, and its host plant was unknown, although Dave had noted that Rubus spp. were present near each collection site. He also noted in the original description that while most sawflies are spring fliers, all specimens of this species had been collected in late September and October. It was a little puzzling, therefore, why Dana’s specimen had emerged in early May, especially since he said it was from a leaf mine he had collected in late March or early April. I wonder now if there was a mix-up and it was really from one of the larvae he had found in January, although even that would be a faster turnaround than I later experienced…

…Because to make sure the biology of Metallus ochreus was properly documented, I collected a large number of larvae mining Rubus hispidus leaves here in Massachusetts in February 2016. Here’s what the mines looked like then; you can sort of see how the early, narrow part of the mine is paler than the rest, although it was much more striking in the examples Dana found:

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It was hard to tell if the mines were occupied without picking the leaves and backlighting them:

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All of the larvae finished feeding and burrowed into jars of soil within two weeks of my bringing them inside. In August, about six months after I’d collected the larvae, 23 adults emerged, and they were all M. ochreus as expected. They presumably would have emerged even later if I hadn’t brought them indoors in February, and this is consistent with Dave Smith’s impression that the species has a single generation with adults only appearing in the fall. This past spring I found some larvae near my house and checked on them every day; they dropped out of the leaves beginning in late April, and the last one hung around until May 3. Add six months to that, and it makes sense that early November is when the leaf mines start to be noticeable.

All this, along with new host and distribution data for the other North American Metallus species, was revealed last week when my latest paper was published:

Eiseman, Charles S. and David R. Smith. 2017. Nearctic Species of Metallus Forbes (Hymenoptera: Tenthredinidae): Biology and Distribution. Proceedings of the Entomological Society of Washington 119(4):551-564.

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