No, Not Leafcutter Bees

Okay, there have been six votes for leafcutter bees being the culprit for yesterday’s mystery sign. Dave Almquist was the only one to qualify his guess: “They look almost like partial cuts from leafcutter bees, assuming that the leaves are small enough for that.” I would agree with that: they do look almost like partial cuts from leafcutter bees (Megachilidae: Megachile), but there are a couple of subtle clues suggesting something else. (They are, in fact, a bit larger than the cuts a leafcutter bee would make, but I realize I didn’t provide anything for scale.)

Here are a few examples of interrupted leafcutter bee cuts, along with completed cuts where the bee removed a circular or oblong piece from the leaf.

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Notice how the pieces are cut all along the leaf margins, in no way focused on the midrib or the major veins. Also notice that the cutouts are made by cutting in one direction: none of the interrupted cuts shows any evidence of the bee starting an opposing cut, and the complete cuts never have a disjointed part in the middle where two cuts didn’t quite line up. In some cases the asymmetry of the cut makes it clear which way the bee was moving (for instance, clockwise in the one in the lower right corner of the second photo). Each of the following photos has another clear example of one of these lopsided, spiral cuts:

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Now take another look at the leaf I found yesterday:

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See how there are two counterclockwise cuts that start at the leaf margin and end at the midrib or a major vein? Each of these has a paired cut that was supposed to meet the first one from the other side. The one associated with the midrib is very short and easy to overlook. The other one made it all the way to the intended vein, but missed the first cut terribly; the insect tried to correct this, but missed again.

On a neighboring leaf of the same oak sapling, the insect got it right:

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This one wasn’t so symmetrical, but it also worked out okay:

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In this second example, it is especially obvious that the leaf cutout was left dangling from the major vein in the middle. What did the insect do while the cutout was dangling like this? Five years ago I posted photos of this insect putting the finishing touches on its creation. When I saw these cut oak leaves yesterday, I knew the finished products should be lying on the ground directly below, but none were in evidence. Apparently they rolled a little when they fell; I picked one dead leaf up off the ground and found this under it:

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This little packet was 8 mm long. Congratulations to Laura Hughes for being the only person to recognize the work of a distracted leaf-rolling weevil.

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Curious Leaf Cuts

A week ago today, I stopped by the Montague Plains Wildlife Management Area on my way home from a meeting. Gray birch and various oaks are abundant there, so I thought I’d look around for leaf mines of eriocraniid moths on the newly opened leaves. It turned out to be a little early for them, but I spotted what appeared to be the very beginnings of the mines of a new species of agromyzid fly Julia and I discovered on honeysuckle in Alabama a few years ago. Today we returned to the same honeysuckle plant and found that some of the mines were already completed,  and they were in fact identical to the Alabama mines. So I collected them (fortunately this species pupates within the leaf), and with any luck I’ll have some Massachusetts specimens to include in the type series when I describe the species with Owen Lonsdale. In the intervening week, the birch-mining eriocraniids had come and gone. Oh well. You’ve got to be quick with some of these leafminers.

Anyway, during our walk I noticed these peculiar curving cuts in a leaf, and I was curious whether anyone can figure out what made them. Unlike most mysteries I post here, I already know the answer, which I’ll reveal in due time…
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Bug Rearing 101

Well, I’ve heard from some people who have found Cecidomyiaceltis deserta galls this spring in Oklahoma, Iowa, and Maryland, but no one has mentioned actually having secured a larva until now. Pete Woods collected several of the galls in Pennsylvania this past weekend and discovered this morning that the first larva had emerged. So, as promised, I’m dropping everything to throw together a page explaining my rearing methods. (Incidentally, if anyone finds these or other mystery larvae I’ve mentioned and doesn’t want to deal with rearing them, I would be happy to take over from there. But people often ask me how I do it, so for a while now I’ve been meaning to make a page like this where I can direct people for answers.)

I collect leaf mines, galls, etc. in standard insect vials (plastic, 9- or 15-dram). If you go looking for these on BioQuip, they’re referred to as “plastic tubes“. You can also get them from Thornton Plastics; if anyone has suggestions of other places to buy them, I’d be happy to add them here. I use a Sharpie pen to write the date, location, and host plant on the lid; this is easily washed off later with alcohol or soap and water when I want to reuse the vial for something else.

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These vials do a good job of retaining the humidity from the leaves, and often nothing more than this needs to be done for a leafminer to complete its development. There is plenty of air in there for an insect to breathe, so no need to punch holes or anything like that. If the leaves (or other host material) are too large to fit in a vial, I put them in a jar or a Ziploc type bag, but if possible it’s best not to complete rearings in bags because adult insects are likely to injure themselves when they emerge (for instance, moths rub off their wing scales, or other insects may deform their wings by cramming themselves into a tight corner).

Some leafminers pupate in the leaves, and in this case you can just wait until the adult emerges. If the leaf starts to dry out (or to prevent a leaf from drying out), I crumple up a square of toilet paper, stuff it in the bottom of the vial, and add a squirt or two of water from an eyedropper. A plastic bag can similarly be humidified with a lightly dampened, folded-up paper towel. For agromyzid flies and certain other things that exit the plant material before pupating, I move the pupae or puparia to a fresh vial with a fresh piece of moistened, crumpled toilet paper. I move puparia from one container to another using a fine-pointed paintbrush; before picking up each one I dip the paintbrush in water. If the larva has spun a cocoon on the vial itself, I leave it in place, removing the plant material to prevent mold and then adding the tissue paper if there wasn’t some already.

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A vial is optimally humid when you can see the slightest amount of fogging on the sides. The vial in the above photo is excessively humid. I use a paper towel to wipe excess moisture from the sides of vials; otherwise there is a risk of the newly emerged adult getting stuck in a water droplet and either drowning or not having its wings expand properly. In the photo below, we’re looking down into the same vial, which contains six puparia of the buckeye-mining agromyzid.

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I check vials once a day to see if anything has emerged or if any humidity or mold control is needed. Many leafminers will emerge as adults within a month or so. These buckeye flies do not emerge until the following spring, and the same is true of the hackberry gall fly (Cecidomyiaceltis deserta) and a number of other insects whose larvae are only active in spring. Species with this kind of life cycle obviously take a little more dedication to rear, and it’s important to check the vials regularly and add drops of water if the tissue starts to dry out. If the tissue starts to get moldy, I transfer the puparia to a fresh vial with a fresh piece of tissue. Erik van Nieukerken uses moss instead of tissue for rearing nepticulids, heliozelids, and other moths. This reduces the mold problem (I’m told), but has the disadvantage of potentially introducing predators, pathogens, or other contaminants to the vial.

Any insects that need to overwinter will need to be exposed to cold temperatures. Their containers could be put in an unheated shed or garage, out of direct sunlight, but then you need to check during warm spells to see if anything is emerging. I like to put everything away for the winter and forget about it, so I use a refrigerator. As far as I know, no insects need to be exposed to freezing temperatures to complete their development, but they need to be exposed to temperatures just above freezing for a certain amount of time. I generally put everything in around November 1 and take everything out around March 1. For a small number of vials or jars, just putting them somewhere in the back of the food fridge would do, but I have a little bug-dedicated fridge in my basement for this purpose. Here’s what it looked like just before I took everything out this spring:

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The fridge is mostly filled with vials in gallon Ziploc bags. In the lower half of the door, you can see a few bags containing larger leaves. On the bottom shelf of the fridge are baby food jars and peanut butter jars containing soil. This brings me to my rearing method for insects other than agromyzid flies that exit their mines or galls to pupate (or are free-living to begin with). Some insects spin a cocoon aboveground, and these I handle in the same way as agromyzid flies. Others (e.g. eriocraniid moths, gall midges, anthomyiid flies, most sawflies, and many weevils and chrysomelid beetles) burrow into soil to pupate. For these, I put a moistened 50/50 mixture of peat and sand in a jar, 3-4 cm deep. The peat helps keep the soil fluffy and its acidity prevents mold from growing. I normally wait until the larvae are mature and wandering around in their original rearing vials before transferring them to a jar of soil, but if I won’t be able to check regularly because of traveling, etc., I put the leaves or galls on top of the soil in the jar, then remove them when I see that the larvae have exited.

The photo below shows a peanut butter jar containing a noctuid caterpillar feeding on a sprig of wintergreen that I’ve “planted” in the peat/sand mixture. These caterpillars take a few months to become full-grown, and I add fresh sprigs of wintergreen as needed. They burrow into the soil when they’re finished feeding and emerge as adult moths about two months later.

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As I already illustrated in my grasshopper post, I take the lids off of the soil jars and put them in Ziploc bags so I can see when adults have emerged. This method, incidentally, is based on the method Ray Gagné has developed for rearing gall midges. I think he has now switched to using 100% peat.

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For groups such as eriocraniids that I know won’t emerge as adults until the following spring, I keep the lids on the jars until I remove them from winter refrigeration. Lidded jars usually retain their moisture well, but those in plastic bags may need a few squirts of water from an eyedropper every once in a while. 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. For the wintergreen moths, I just leave the lid on the peanut butter jar, but have to check under the lid every day because this is likely to be where the moth comes to rest when it emerges.

If I’m not sure what an insect’s pupation habits are, I put it in a jar of soil with a piece of crumpled-up tissue paper on top of the soil. Almost all insects will either burrow into the soil or make a cocoon in the tissue or on the soil surface. Some sawfly larvae need a chunk of punky wood to burrow into; Dave Smith recommends providing pieces of cork for this purpose. There is an introduced leafminer on honeysuckle, Perittia herrichiella (Elachistidae), that I had a hard time rearing until I learned that it makes a cocoon on the bark of its host plant, camouflaged with bits of bark. So last fall I put some strips of honeysuckle bark in a vial and added the larvae as they emerged from their mines. The cocoons were so well camouflaged that the larvae just seemed to disappear after I put them in the new vial, but sure enough this spring they’ve all emerged as adults.

I think this pretty well covers it, but I’ll be happy to add further details if anything needs clarification. If anyone has had success with other rearing methods, I’d be interested to hear about them. I’ve done very little with wood-boring and stem-boring insects, for instance, and obviously some different strategies would be needed for these.

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Things To Look For This Spring, Part 3

First, a quick update on the hackberry galls: Mike Palmer has found a bunch of them in Oklahoma, and in fact they may already all have been abandoned there. Some of them have holes near the base, and others have the beginnings of holes in the same place, clearly made from the outside, as if something was trying to get in but gave up. We’re hanging onto them just in case there are some agromyzid larvae left inside, but in any case, I now have a picture of one to reinforce the search image for those of you who are keeping an eye out for them:

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The withering leaves beyond the galls may be the easiest way to spot them. For anyone who finds some to collect, I would recommend cutting the twigs several inches below the gall and putting them in a resealable plastic bag right away to retain moisture. The larvae seem to develop pretty quickly, so I would say go ahead and collect any you find, rather than waiting to make sure they are mature.

Here is the underside of the same gall, showing the presumed larval exit hole:

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Anyway, the third and final(?) thing I’d like you to keep an eye out for this spring is something that has been bugging me ever since I got going on this leafminer business five years ago. During my first visit to Nantucket in September 2011, I got a ride over to the little island of Tuckernuck to spend a few hours looking for insect signs there. One of the leaf mines I found there was this contorted, narrow, linear one on arrowwood (Viburnum dentatum):

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Over the following winter, as I began reviewing all the published information on North American leafminers, it became clear that this wasn’t a mine that anybody knew about. So when I returned to Nantucket in early August of 2012, I made a point of looking for more examples, and I found them to be abundant there. I noticed that they always ended up at the midrib near the base of the leaf, and on close inspection I could see that the mines continued down the petiole.

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As you can see in the above photo, the mine continues for a short distance in the petiole and then goes deeper in the plant tissue, where it can’t be followed anymore. Some mines were visible for longer than others, and after examining several it was clear that this species follows the petiole down into the twig, where it continues to mine deep in the bark. So I cut several sprigs of arrowwood as described above for the hackberry galls—several inches below the mined leaf, with the hope that the mining larvae were still inside. Over the next few weeks, I found three different types of larvae in the bag. There were these yellowish ones, about 1.35 mm long…

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…these whitish ones, which were even smaller…

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…and a single one like this, about 1.5 mm long:

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Eventually I realized that the yellowish ones were larvae of Sackenomyia commota (Cecidomyiidae), the midge responsible for these blisterlike galls on arrowwood leaves:

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The whitish ones may have been larvae of another, inquiline midge species, or possibly of a parasitoid wasp. The third larva, however, bore a striking resemblance to a Marmara larva I’d seen illustrated in a paper. Marmara is a genus of mostly bark-mining moths in the family Gracillariidae, subfamily Gracillariinae. Since I knew Dave Wagner and Don Davis are working on this group, I asked them for their opinion. They both agreed that it looked like Marmara, but neither of them was aware of a Marmara on Viburnum—the only gracillariid recorded from that host is Phyllonorycter viburnella, which is said to be rare even where arrowwood is common, but like many normally rare things, it is common on Nantucket:

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About the Marmara, Dave commented: “If the Viburnum feeder proves to be localized to Nantucket and Tuckernuck Island—a biogeographically bizarre distribution—it would not totally surprise me.  Out West there are many Marmara that exhibit such localized distributions.”

The Marmara larva I had photographed was nowhere near mature, and having seen Marmara bark mines on other hosts like ash and pine, I knew they can be very long—it was no wonder the sprigs I had collected hadn’t been big enough for the larvae to complete their development. Marmara species typically have a year-long life cycle that involves overwintering in the bark, then continuing to feed in the spring and transforming to an adult around June.

In June of 2013, I returned to Nantucket and found that there were in fact bark mines visible on some arrowwood plants, though mostly for short stretches; it was clear that most of the feeding trail was too deep to see, and following it to its end would be impossible.

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Some Marmara species conveniently spin their cocoons at the ends of their mines, but others exit the mine and wander off before pupating, and there was no way to know what this one did. I searched the plants that had visible bark mines, but I didn’t see any signs of cocoons, so I assumed this was a species that wanders off.

The following month, I was doing fieldwork in southeastern Massachusetts (the same job that brought us Orchestomerus eisemani and the scuttle flies I wrote about a few weeks ago) and I spotted some more of the leaf mines—the first examples I’d found off the islands. I collected some more sprigs, knowing I wouldn’t be able to raise larvae to adults, but hoping that once again one would pop out of the bottom of a twig, and this time I’d preserve it for DNA barcoding, to see if it could be matched with some adult Marmara specimen. None ever materialized, but two of these did:

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Recognizing from the horn at the back end that they were some kind of sphinx moth (Sphingidae) caterpillar, and knowing that the host was Viburnum, it was easy to identify them (using Dave Wagner’s guide to eastern caterpillars) as immature hummingbird moths (Hemaris thysbe). I’d had no idea what hummingbird moth caterpillars looked like before then.

On one or two of the Nantucket arrowwood plants, I had seen the Marmara mines going within a few inches of the ground before disappearing again. I mentioned this to Dave, and he thought it was likely that this species overwinters in the bark of the roots. This is not unheard of; the mine of M. basidendroca on green ash (Fraxinus pennsylvanica) extends up to 7 cm below ground before resurfacing for pupation and emergence of the adult.

It looked like drastic measures would be required to learn the identity of this moth. So in the summer of 2014, Julia and I returned to Nantucket and tied pink flagging on several arrowwood plants that had leaf mines. Unfortunately, the mines weren’t nearly as common that year as they had been in 2012. Julia returned in December and dug up and potted the flagged plants. Meanwhile, I had found a few examples of the mines in the Berkshires of western Massachusetts—on wild raisin (Viburnum nudum) and hobblebush (V. lantanoides) as well as on arrowwood—and I had potted a couple of those too. Julia sewed some bags from transparent fabric to surround the potted plants and trap any emerging insects. We kept the plants in our shed all winter.

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Last spring, we brought all the bagged plants into our kitchen and checked them several times a day for any signs of life.

On April 2, this 6-mm sawfly emerged—a male, given its fancy antennae. Dave Smith identified it as a species of Monoctenus (Diprionidae), which would have fed as a larva on juniper foliage, then burrowed into the soil among the arrowwood roots to overwinter and pupate.

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On April 13, this 2-mm wasp emerged. I thought it might be a parasitoid of the Marmara, but it turned out to be an Encyrtus (Encyrtidae), which must have emerged from a scale insect on the bark of the arrowwood.

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Toward the end of April, a moth finally emerged—but it was a tortricid, not a Marmara.

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Specifically, this 8-mm moth was Zomaria interruptolineana, whose larva is a leaftier on blueberry and huckleberry, both of which are abundant on Nantucket. Coincidentally, I’d photographed this same moth species on an arrowwood leaf on June 10, 2013, at the same location where Julia dug up that plant.

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But alas, no Marmara adults ever emerged.

Last July, on our way to Colorado we stopped at a rest area along I-70 in Illinois. The border of the picnic area was lined with forest, so we walked along it to see what leaf mines we could find. There were a couple of arrowwood plants, and we found a few of the Marmara mines. Then, much to my surprise, we found two Marmara cocoons! The species that pupate at the end of their mines make their cocoons under a little bark flap, like so:

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Since this species is sneaky and its mines mostly aren’t visible on the bark surface, it was just dumb luck that we noticed these. Where the bark has been removed in the above photo, you can see a few dark lines, which are the frass trail from the larva’s mine. To give a sense of the scale, as well as a view of the white silken cocoon beneath the bark flap, here’s a shot with my finger holding the bark flap back:

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Of course, both cocoons were already empty, so we had no hope of getting adults from them, but now we know there’s no need to dig up the plants to rear them; we just need to search more carefully for these bark flaps in the spring.  These were several feet off the ground, so apparently the larva doesn’t always mine all the way to the roots—or if so, it may mine all the way back to the height of its original leaf mine.

A closer look at the cocoon under the bark flap reveals that it is decorated at either end with “frothy bubbles.”

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These “bubbles” are expelled through the walls of the cocoon, for unknown reasons, by the larvae of certain genera of Gracillariinae. Interestingly, the Marmara species that spin their cocoons under bark flaps at the end of their mines aren’t supposed to make these bubbles, so it seems pretty clear that this is a new species rather than a described one using a previously undocumented host plant.

Here is a photo of the cocoon of another gracillariid that shows the “bubbles” more clearly:

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When backlit, you can see that they are faceted like little jewels:

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Anyway, if you have any kind of viburnum near you, please keep an eye out for these bark flaps this spring. Of course, it would be easier to know which plants to look at if you had flagged plants that had leaf mines on them last year, but maybe you’ll luck out as we did in Illinois. For whatever reason, I’ve never found the mines in the central part of Massachusetts where I live, even though I’ve found many examples in the extreme western and eastern parts of the state.

And if you don’t have viburnum near you, I’m sure there are many more Marmara species left to discover. In fact, I’m pretty sure the number left to discover is larger than the number that already have names, based on bark mines I’ve found on host plants from which Marmara adults have never been reared. When the mines are fresh (and when it’s not a sneaky species that mines too deep in the bark to see), the larva can be seen through the bark epidermis, as in this example on Ceanothus sanguineus from Oregon (also not a known host for any barkminer):

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Not all bark mines are caused by Marmara species; they can also be the work of other moths such as Zimmermannia, a subgenus of Ectoedemia (Nepticulidae). Or possibly something else. I’m including bark mines in the keys in my leafminer book, because let’s face it, no one is ever going to write a whole book about bark mines.

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Things To Look For This Spring, Part 2

Another thing on my wish list for this spring is a leaf-mining lauxaniid fly larva. The Lauxaniidae are very common flies, with over 150 species occurring in North America, yet as far as I know there are no common names for the family or any of the species in it. Most species are only known from adults, but members of at least six of the 30 genera that occur here have been reared from leaf-mining larvae. Unlike most leafminers*, lauxaniids mine in decomposing leaves on the ground. They probably are not very host-specific, but most of the North American species that have been reared have been found mining maple and black cherry leaves (in Europe, they have also been found in apple and willow leaves). I have found no illustrations or descriptions of the mines, which is the main reason I’d like to see some in person (I also just think they’re nice flies and would like to get to know them better). Some species appear to have multiple generations per year, but others have just one, and larvae of these species do most of their feeding in the spring. I’m not sure if the larvae could be found in the top layer of leaves (and therefore possible to spot while walking through the forest) or if you would have to sift through the leaf litter to find them. I’ve spent a little time looking this spring without any luck. The flies are ubiquitous, though, so the larvae must be too.

Here are examples of four genera that include leaf-mining species:

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Camptoprosopella (southern Arizona, November 4, 2012)

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Camptoprosopella (Tennessee, May 28, 2011)

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Homoneura (Tennessee, May 29, 2011)

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Homoneura (western Massachusetts, August 29, 2011)

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Minettia (western Massachusetts, July 11, 2011)

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Minettia (northwestern Washington, October 6, 2012)

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Sapromyza brachysoma (western Massachusetts, January 19, 2011)

It’s hard to tell in the photo, but this one was on snow. I spotted it while shoveling, and had to go and get my camera when I saw its stripey eyes:

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* A few weevils also mine in dead leaves in leaf litter. I’d love to find some of those too.

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Things To Look For This Spring, Part 1

I have a pretty much endless mental list of natural history mysteries that I would like to follow up on at some point, but there are several that, for various reasons, are in the front of my mind right now. A few of these are things that should be looked for in the spring and that I think it’s unlikely I will have a chance to look for this year. So I thought I would put them out there, one at a time, for those of you who like to have a mission when you go out exploring. As an extra incentive, if anyone is able to find larvae or pupae of any of the insects I have in mind, I promise to drop whatever I’m doing at the moment and make a page on this website detailing my methods for rearing leafminers, gallmakers, and other insects.

First up is Cecidomyiaceltis deserta, a fly that causes twig galls on hackberry (Celtis occidentalis). There are some photos of the galls here. If we know the fly’s name and what it does for a living, you ask, what is the mystery? Well, C. deserta was described in 1897 by William H. Patton, an amateur entomologist in Connecticut, in a short paper in which he proposed a system for naming galls whose causers were unknown*. The system involved combining the name of the insect group with the name of the host plant, and so from Cecidomyiidae (gall midges) and Celtis (hackberry) he coined the genus name Cecidomyia-celtis. The description of C. deserta consists of just two sentences:

Galls are hollow, elongate swellings of young twigs, from which emerge, about the first of June, single Cecidomyian flies from a perforation near the base. Length of gall one half inch to one inch.

That sort of thing doesn’t fly anymore, but according to the International Code of Zoological Nomenclature, species names based on the work of an animal are valid if they were proposed before 1931. In the same 1897 paper, Patton named five other hackberry galls that had been described, but not named, in a previous publication. He placed all of these in the genus Cecidomyiaceltis.

All six of the species names Patton proposed for hackberry gallmakers are still considered valid. The problem is that in the spring of 1982, Ray Gagné determined that Cecidomyiaceltis deserta is actually an agromyzid fly (agromyzids are commonly known as “leafminer flies,” but some have other habits including gallmaking). He noticed the galls forming in the Washington, DC area in the second week of April, and the larvae exited at the bases of the swollen twigs in the first week of May. Unfortunately he was unable to rear adults, but the larvae formed puparia, and agromyzid puparia are easily distinguished from the naked pupae of gall midges. Since Patton apparently did not preserve any insect specimens associated with his galls, we can only speculate as to whether he saw the agromyzid larvae emerging and mistook them for gall midge larvae, or possibly only saw the exit holes and assumed that “Cecidomyian flies” had emerged. Because C. deserta was the first described species of Cecidomyiaceltis, it is the type species of that genus, and Gagné had to create a new genus, Celticecis, for Patton’s other five species, which really were gall midges. As I discussed in this post, there are now 21 recognized species in Celticecis***. Two of Patton’s species, C. spiniformis and C. capsularis, are featured in that post.

The upshot of all this is that someone needs to rear adults of Cecidomyiaceltis deserta to find out what they look like, and then we can determine what genus they actually belong to. Maybe they will turn out to be related to this fly, which I believe to be Agromyza varifrons—it emerged yesterday from a hackberry leaf mine I found at Marcie and Mike O’Connor’s place in Wisconsin last July:

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There isn’t any native hackberry growing anywhere near me, which is why I’m putting out this call for help. In addition to the east coast records mentioned above, these galls have also been found in Kansas (where they were believed to be the work of some unknown moth), so it is probable that these galls could be found anywhere that hackberry is common. Who’s up for the challenge?

* Patton, W.H. 1897. A principle to observe in naming galls: two new gall-making Diptera. The Canadian Entomologist 29: 247–248. [online here]

** Gagné, R. J. 1983. Celticecis (Diptera: Cecidomyiidae), a new genus for gall makers on hackberries, Celtis spp. (Ulmaceae). Proceedings of the Entomological Society of Washington 85: 435–438 [online here].

*** Gagné, R. J. and J. C. Moser. 2013. The North American gall midges (Diptera: Cecidomyiidae) of hackberries (Cannabaceae: Celtis spp.). Memoirs of the American Entomological Society 49: 1–103. [online here].

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More Fun With Scuttle Flies

The first days of April have brought January weather to my region and the January issue of Proceedings of the Entomological Society of Washington to my mailbox. The latter includes descriptions of a new species of gall wasp that has recently become abundant on oaks along the New England coast, as well as a new species of midge that causes flowerbud galls on joe pye weed. It also includes my second collaboration with Emily Hartop (this time with Maria Wong as well) involving scuttle flies (Phoridae)*.

It all started when I was at work one day (July 18, 2013, to be precise) in southeastern Massachusetts and came across this little scene on the underside of a dangleberry leaf (Ericaceae: Gaylussacia frondosa):

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The large, furry object is the remains of a white-marked tussock moth caterpillar (Erebidae: Orgyia leucostigma) that had begun to construct its cocoon (made of white silk mixed with black, clubbed hairs plucked from its own body) when it succumbed. To what had it succumbed? This was answered by a dozen tiny black objects that were scattered around the caterpillar’s remains, mostly on the leaf beneath the caterpillar, but one was stuck to a few of the caterpillar’s long hairs and is plainly visible in the above photo. Here’s a closer look at that one:

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These black objects are the pupae of eulophid wasps that fed as larvae inside the living caterpillar. To find out what kind, I picked the leaf and stuck it in one of the vials with which my backpack is always well supplied. Along with the leaf, dead caterpillar, and wasp pupae came a little scuttle fly who can be seen just to the left of the caterpillar in the first photo. She was sufficiently interested in the caterpillar that she didn’t try to escape as I picked the leaf. I assumed she was laying eggs on the carcass, and that her offspring would feed on it.

Sure enough, eight days later I noticed several little fly larvae in the vial.

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The next day, all twelve of the eulophid wasps emerged from their pupae.

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I sent them off to Christer Hansson, who reported that they were all females of Elachertus cidariae. This species was already known to parasitize caterpillars of Orgyia leucostigma as well as ten other moth species.

Four days after the wasps emerged, the fly larvae began to pupate. Here is one with its body beginning to contract:

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…and here is a finished puparium, showing the spiracular horns characteristic of phorid flies. (I didn’t crop this one more closely because I liked the detail of the feathery club at the tip of the black caterpillar hair.)

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Between August 17 and 19, six adult scuttle flies emerged—three males and three females. The females were the same species as the original female I had collected, and in all probability were her offspring and were siblings of the males… but as we’ll see in a moment, extreme caution is warranted when trying to identify female scuttle flies.

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I sent the flies off to the Los Angeles Natural History Museum, along with the one that Emily and I later described as Megaselia nantucketensis. In July of last year, Emily informed me that they appeared to be another new species, and the same as a couple of specimens that had recently been collected in Los Angeles. At the end of August, we had a paper about ready to submit that would have given this species a name, when Emily came across the suspiciously similar holotype of Megaselia globipyga, which had been collected in Idaho in 1919. A holotype is the type specimen, on which the original description of a species is based. The type series can also include any number of paratypes, which are other examples of the species examined by the species author while preparing the description. Emily had previously ruled out M. globipyga on the basis of existing keys to Megaselia species and (I believe) comparison with one or more paratypes. After slide mounting the holotype, however, she discovered that my flies (along with five from Los Angeles) matched it. Further investigation revealed that none of the paratypes were actually the same species as the holotype (with the possible exception of one that is in Brazil  and another that is missing from its pin and presumed lost). One paratype from Montana was in poor condition but appeared to be M. atrox, and the remaining two (from Washington and Idaho) belonged to an undescribed species.

The rest of this story has nothing to do with my Massachusetts flies, but it further illustrates how much work is left to do in insect taxonomy, and why you may not always get a straight answer if you send a specimen to a specialist for identification. On further investigation, Emily found that one of the paratypes of Megaselia postcrinata belonged to the same undescribed species as the two M. globipyga paratypes. The rest of the M. postcrinata paratypes belonged to three other species, and any of the four might be true M. postcrinatabut the holotype is a female, and modern taxonomy of Megaselia is largely based on male genitalia. So the status of M. postcrinata will be uncertain until someone is able to definitively associate a male with a female that matches the holotype. In the meantime, our paper designates the first paratype of M. postcrinata as the holotype of a new species, M. risoria (risor is Latin for “one who laughs”; so named because a little line on this fly’s thorax—the notopleural cleft—looks like a smile). The paratypes of M. risoria include the two aforementioned paratypes of M. globipygaas well as a specimen recently collected in Los Angeles. Although I am technically a coauthor of M. risoria, I can take absolutely no credit for this taxonomic wizardry.

This week I’m sending Emily another set of scuttle flies, which emerged last month from larvae I collected last May. What can of worms am I opening this time?  We shall see…

* Hartop, Emily A., Maria A. Wong, and Charles S. Eiseman. 2016. A new species of Megaselia Rondani (Diptera: Phoridae) from the BioSCAN Project in Los Angeles, California, with clarification of confused type series for two other species. Proceedings of the Entomological Society of Washington 118(1):93-100.

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