Ragweed Residents

This is the time of year that everybody is ragging on ragweed (Ambrosia spp.)—at least, everyone who realizes that it is the pollen of this plant, and not goldenrod, that is responsible for their summer allergies. At times like this, when some may feel like ridding the world of ragweed entirely, it’s good to remember that every native plant has a whole community of insects that depend on it.

Last August I noticed some striking little fruit flies (Tephritidae) hanging out on the ragweed in my yard:

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These flies are Euaresta bella, whose only known host is common ragweed (Ambrosia artemisiifolia). The females lay eggs in female flowers and the larvae develop in the fruits, where they overwinter, pupating in the spring. The females in the last two photos above are on male flowers, which produce the dreaded pollen and presumably are not suitable oviposition sites.

Another species that feeds only on common ragweed is the leaf beetle Ophraella communa (Chrysomelidae). It lays clusters of yellow eggs on the foliage (these empty eggshells aren’t quite as yellow)…

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…which produce hairy larvae that feed on the leaves.

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Ophraella species are unusual among beetles in that they pupate in cocoons on their host plants (most beetles do not spin cocoons, and/or pupate in a cell hidden from view).

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The adults are stripey and likewise feed on ragweed foliage.

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Here’s an aphid that was sucking away on a ragweed stem in my yard last summer. It’s probably a Macrosiphoniella species, or possibly Uroleucon, according to Natalie Hernandez. Not being sure what it is, I can’t comment on its host specificity.

IMG_6173 And then, of course, there are the leafminers. I count 30 North American species that are known or suspected to mine leaves of various ragweeds. Not all of these are specific to these hosts, but Astrotischeria ambrosiaeella (Tischeriidae) is an example of one that is. As far as I know it doesn’t occur in New England, but Julia and I found the distinctive mines on giant ragweed (Ambrosia trifida) at a rest area along I-70 in Missouri.

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In the middle of the brown mined area is a green “nidus,” a silken retreat in which the larva ultimately pupates. The related species Astrotischeria heliopsisella, which mines leaves of sunflowers as well as ragweeds, eats the leaf tissue above the nidus so that it appears white instead of green. One of the mines in the above photo produced this adult moth:

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The other mine produced this parasitoid:

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The only chalcid parasitoid recorded from Astrotischeria heliopsisella is Pnigalio maculipes (Eulophidae). I think the one I reared is probably a Pnigalio, but probably not P. maculipes, since it doesn’t have the spotted legs that give that species its name. The genus Pnigalio needs revision anyway; the last set I gave Christer Hansson (reared from this eriocraniid) consisted of two species that couldn’t be identified using existing keys. Anyway, the point is, lots of bugs eat ragweed.

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Fungus Gnat Train

It’s been two and a half months since my last post—not, of course, because I’ve run out of things to write about, but because there’s too much going on at this time of year for me to find the time to write anything. To compound this busy-ness, Julia and I took a nearly three-week road trip last month to look for leafminers in Colorado and the Midwest. Ever since we got back, emerging leafminers have taken up most of the waking hours that I haven’t been at work. But since this blog has just reached 500 subscribers, I thought I’d throw together a little something to mark the occasion.

On July 1, we met up with ant taxonomist and all-around great naturalist James C. Trager at Shaw Nature Reserve just west of St. Louis, Missouri. Toward the end of our walk, we happened on something I’ve been wanting to see for a long time: a wriggling mass of dark-winged fungus gnat (Sciaridae) larvae on the move.

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A year ago, I asked Rob Deady (as far as I can tell, the only person in North America who studies dark-winged fungus gnats) about this phenomenon. He said that the behavior seems always to be triggered by water, and indeed it had just been raining a few hours before we encountered these larvae.  In these masses, the larvae crawl across a film of mucus that they secrete, probably in search of a drier area to pupate rather than to continue feeding, but this apparently hasn’t been studied very thoroughly. The behavior is exhibited by many Sciara species, including S. militaris and S. thomae, as well as members of other genera such as Bradysia bicolor, Cratyna perplexa, and Ctenosciara hyalipennis.

My camera has no video feature, but after taking the above photos I borrowed Julia’s camera and made a couple of short, shaky videos with it. Below, you can watch the most in-focus parts, which Julia edited together with a much better clip that she made by resting the camera on the ground (that one comes first, so you don’t have to get seasick right off the bat).

For more examples of this phenomenon, see this BugGuide page, which includes several instances of the larval masses forming perfect circles.

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More Sawfly Art

Two years ago I posted this photo of a sawfly larva feeding on a black cherry (Prunus serotina) leaf on Nantucket. I suspected it was Sterictiphora prunivora (Argidae), based on Harrison G. Dyar’s (1897 ) description of that species eating a “curious winding slit down into the leaf.” I collected the larva to try and raise it, to confirm this suspicion.

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These larvae have been active for the past week or two here in western Massachusetts, so I figure it’s time to report on my findings. But first, here are a few examples I’ve found this month (beginning on May 18):

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So back to the Nantucket larva from two years ago. As it grew, it abandoned its distinctive feeding style and became a regular old leaf edge feeder. This picture was taken one week after I collected it:

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Four days later, it spun a fuzzy brown cocoon in the bottom of the vial:

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The adult sawfly emerged the following spring:

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Dave Smith determined it to be Sterictiphora serotina, a species he had first described in 1969. As evidenced by its name, it was known to feed on Prunus serotina, but the details of its life history had not been recorded. Possibly these “curious winding slits” are made by all species of the genus Sterictiphora, of which there are six in North America and about forty worldwide. Another member of the subfamily Sterictiphorinae, Aproceros leucopoda,  feeds in a similar pattern on elm leaves. It is native to Asia but has recently spread throughout Europe, where it has become known as the “zigzag elm sawfly.”

Dave also sent me a scan of a page from Dyar’s notebook, on which Dyar had sketched the original “curious winding slit.” I included this sketch in a note that was recently published*–actually it was published the day after the paper describing Scolioneura vaccinii, along with another paper Dave and I coauthored on the violet leafmining sawfly. It was a good week for sawflies.

If you would like a PDF of one of these, or any other of my journal articles that are not open access, just send me an email.

* Eiseman, Charles S. 2015. On the distinctive feeding pattern of Sterictiphora Billberg (Hymenoptera: Argidae) sawfly larvae. Proceedings of the Entomological Society of Washington 117(1):65-67.

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A Complete Guide to Things That Eat Sea Lavender

Before I get started here, I wanted to point a few things out:

1. If you have an email subscription to this blog, I highly recommend clicking on the title rather than just reading the version that shows up in your email. This is because I have a habit of continuing to make little changes and additions after a post is published. (This habit isn’t limited to BugTracks; I can’t seem to stop working on Tracks & Sign of Insects either, even though it was published over five years ago.) For instance, when I woke up the morning after writing my last post, I tacked on another possible explanation at the end. I had gone back and forth about whether I should mention it, but everyone who has commented has agreed with this last hypothesis.

2. It has recently come to my attention that at least one ad-blocking program hides the email subscription box that should appear in the right sidebar, so if you haven’t been able to figure out how to subscribe, just disable your ad-blocking software and you should see a place to enter your email address and a “Sign me up!” button right above the “Make a Donation” button. I pay an annual fee so that you don’t have to see annoying ads on my website, so there is no need to use an ad blocker here.

So anyway, you may recall that a year and a half ago, I wrote about some mysterious mines in sea lavender leaves, which I’d found along the Maine coast and on Nantucket. Here’s one example:

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I had first noticed the mines in June 2012 on tiny (2-acre) Battle Island, on which I was conducting a natural resource inventory for the Maine Coast Heritage Trust. The island is connected to the mainland at low tide, so I had decided to walk on in the morning and maroon myself there until the tide went back out in the evening. After two hours, I had thoroughly documented every plant and vertebrate on the island, so I was free to play with my macro lens and look for leaf mines for the rest of the day.

In 2013 I found more empty sea lavender mines on Nantucket, and then last June, while working on Ram Island in Castine, Maine, I finally found some that looked like they must be fresh, though I couldn’t see the larvae inside them:

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I’m sure I wouldn’t have noticed these little white wispy lines in the leaves if I hadn’t been obsessing about these mines for the past two years.

By the end of June, the larvae were clearly visible in their mines.

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The leaves were starting to get moldy and deteriorate, but Kelly Omand of the Nantucket Conservation Foundation saved the day by FedExing me some fresh leaves, which I kept in the fridge, allowing me to refresh the rearing vials as needed. Over the next two weeks, the larvae exhibited a variety of behaviors, including leaf mining, petiole and midrib boring, leaf tying, and feeding on the leaf surface beneath a web. By mid-July, some were full-grown.

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I had stuffed a crumpled-up piece of toilet paper into the bottom of each rearing vial to absorb excess moisture from the decomposing leaves. The mature larvae burrowed into the paper to pupate, beginning in mid-July.

Later in July, a single adult emerged.

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I knew it was a tortricid moth, but that was all I knew. I sent it to John Brown at the Smithsonian, along with the buckeye petiole borer, and he identified it as Gynnidomorpha romonana. This is the first larval host record for this moth, which is the only member of its genus in North America. Sea lavender must not be the only host plant, though, because G. romonana occurs as far west as Manitoba and Illinois, where there certainly isn’t any sea lavender.

It turns out that no insects have previously been documented feeding on sea lavender in North America (apart from flower visitors). But on that day in June 2012 that I took inventory of every bug on every plant on Battle Island, I found some aphids sucking on the sea lavender stems. When I returned in August, they were on the leaves as well.

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These photos document the first time I’ve watched an aphid giving birth, but they also document something more significant: the first record of the aphid genus Staticobium in North America. Fortunately, over the summer I had corresponded with aphid taxonomist Andy Jensen about these, and I knew they were something interesting before I returned in August. So I collected some for him to examine. Unfortunately, the genus is a mess, and he was unable to determine whether they represent a new species or one that occurs in Europe. I do not think they represent a recent introduction; it just seems like no entomologists have paid attention to sea lavender before. I have since found more of these aphids elsewhere on the Maine Coast and on Nantucket, and some were collected in Nova Scotia last summer.

For more details about all this, see:

Eiseman, Charles S. and Andrew S. Jensen. 2015. Insects feeding on sea lavender (Plumbaginaceae: Limonium carolinianum [Walt.] Britt) along the New England coast. Entomological News 124(5):364-369.

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Turrets Topped With Pebbles

Here’s another little mystery for y’all. Two months ago, Sheryl Smith-Rodgers posted to BugGuide’s ID Request the following three photos, which she had taken on March 10. These structures were found in a dry creek bed on a ranch in Mason County, smack in the middle of Texas. Each consisted of a pillar of sand and small pebbles, with a larger pebble forming a roof.

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Unfortunately, that’s all we have to go on. We don’t know for sure that these are hollow turrets at the entrances to burrows, but it seems like they probably are. The first thing that came to my mind was that some kind of trapdoor spiders were using pebbles as lids to their burrows, and my fellow BugGuide editor Lynette Schimming had the same thought. But on further reflection, it seems to me that trapdoor spiders make their burrow entrances flush with the ground, and the related spiders that make turrets are the folding-door spiders (Antrodiaetus). Their turrets have flexible collars rather than lids, and apparently none of them occur in Texas, based on the map on page 397 of Coyle (1971)*.

These structures seem vaguely familiar, in a way that causes some inaccessible part of my brain to itch… possibly I came across them at one point and tried to forget about them because I couldn’t make sense of them. My favorite hypothesis at the moment is that these are pupal shelters of caddisfly larvae, which would have been active when there was water in the creek. On page 260 of Tracks & Sign of Insects there is a photo of a pupal shelter of a net-spinning caddisfly larva (Hydropsychidae), likewise consisting of tiny pebbles with a much larger pebble for a roof. As far as I know, however, hydropsychids don’t make anything approaching the height of these turrets. Larvae of Phylocentropus caddisflies (Dipseudopsidae) live in tubes that project vertically from sandy stream bottoms; might they ever put lids on their burrows when they’re ready to pupate? Any other ideas? Could they possibly just be the result of erosion–a miniature version of this? If only we could  peek under one of those pebbles…  [Edit: See John Pearson’s explanation supporting this last hypothesis in the comments below. I had noticed the sorting by particle size too, and wondered if that might be what was happening.]

* Coyle, Frederick A. 1971. Systematics and natural history of the mygalomorph spider genus Antrodiaetus and related genera (Araneae: Antrodiaetidae). Bulletin of the Museum of Comparative Zoology 141(6):269-402.

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Buckeye Bugs To Watch For

This time last year, I wrote about some drooping Ohio buckeye leaves I had just found in Ohio, which I later determined to be caused by Zeiraphera claypoleana, the “buckeye petiole borer.” Commenting on my original post, Moni Hayne mentioned finding some leaf mines on Ohio buckeye in Iowa, and I encouraged her to post them on BugGuide.net. She did, and it is clear from her photos that the miner is an agromyzid fly. The problem is, no agromyzids are known to mine buckeye or anything related to it. Before long, two other Iowans, John Pearson and MJ Hatfield, had posted photos of similar mines. Here is one of John’s:

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These gradually widening, linear mines are easily distinguishable from the two other mines that have been documented on buckeye, both of which are made by moths in the family Gracillariidae. Cameraria aesculisella makes an elongate blotch, pupating within the mine, whereas this agromyzid exits to pupate. The mine is very similar to that of its close relative, C. guttifinitella, on poison ivy:

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In Illinois, Terry Harrison has reared a moth from Ohio buckeye that is indistinguishable from Caloptilia negundella, which feeds on boxelder. As with most Caloptilia species, C. negundella makes a small blotch mine on the underside of a leaf, then abandons it and feeds in a conical roll at the tip of the leaf:

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Based on what I have seen so far, the fly larvae are only active in May. In addition to the Iowa sightings, this photo by Jason Dombroskie from Ontario appears to show the same mines, likewise in May. I was already planning to send out a plea for people to keep an eye out for these mines this month, when today a fourth Iowan, Aaron Brees, sent me photos of two examples he has found in the past week. So I figured I’d better put the word out now: if there is any buckeye near you, please take a look in the next week or so and collect any linear leaf mines you find (with larvae still inside them)! If you find any, place the leaves in a ziploc-type bag or a collecting vial right away; this will prevent the leaves from wilting, and they should last long enough for the larvae to complete their development. Then get in touch with me, and we can discuss what to do next.

If you do go out to inspect some buckeyes, here’s something else to look for: at least two BugGuide contributors have photographed sawfly larvae in the genus Dimorphopteryx feeding on buckeye, but this is not a known host for this or any other sawfly genus. They have been found in Lousiana in mid-May, and in Ohio in late June (so they may not show up until after the agromyzid leafminers are gone). The larvae have the general look of the ones below, which were feeding on oak and chestnut.

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Holey Leaves

In S.W. Frost’s excellent 1959 book, Insect Life and Insect Natural History, there is a drawing of a clover leaf with a radially symmetrical pattern that gives the impression of a bite having been taken out of each side of each of the three leaflets. It is said to have been caused by a weevil feeding on the leaf before it opened (the weevil is said to be Hypera punctata, which apparently is now Donus zoilus, the clover leaf weevil). Here is an example I found with the opposite pattern, caused by damage to the tips rather than the edges of the still folded-together leaflets:

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Last fall, I found a beech leaf with a more elaborate pattern, apparently caused by a single hole in the bud, producing an effect like a paper snowflake:

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I thought that was pretty impressive until the other day, when John Maxwell brought to my attention this photo of a banana leaf, taken by Keara Giannotti in the Monteverde Cloud Forest Reserve in Costa Rica:

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Keara says this was the third leaf she found with a similar pattern. She found this web page that attributes similar holes in a banana leaf to the caterpillar of an owlet moth (Noctuidae), Spodoptera litura. I find it fascinating that the holes line up perfectly in perpendicular rows and columns, which (unlike the holes in my beech leaf) have nothing to do with the leaf venation. Curiously, in the upper left there is a set of additional, alternating holes on one side of the midrib, and at the very top left (again just to one side of the midrib) there is an extra row of holes that is slightly offset.

So, beyond the question of what insect is responsible, I wonder how many separate “chomps” this pattern represents? Maybe someone with access to unfolding banana leaves will experiment with poking some holes and report back to us?

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