A South Texas ID Frontier: Leaf Miners

Texas (and Texas-visiting) iNatters: We have a big ecological mystery on our hands. Most of the leaf-mining insects found on iconic Texas plants like Anacua, Mexican Olive, Coma, Zanthoxylum species, and even roadside composites like Palafoxia are poorly known or in some cases perhaps even new to science.

I found this leaf miner yesterday (12/29/20) on a Bernardia myricifolia plant at Resaca de la Palma State Park in Cameron County. The larva is visible near the top of the translucent mine. Its identity is unknown, though leaf miner expert Charley Eiseman thinks it may be a moth in the family Heliozelidae.

You may recall leaf structure diagrams like this from your biology textbooks -- a few cells, stacked in discrete and specialized layers, the whole thing often just a couple hundred micrometers thick:

Image CC-BY-SA Zephyris

Leaf miners are the larvae of insects -- moths, flies, sawflies, and beetles -- that are so tiny they live between the epidermal layers of the leaf, eating the cells of the mesophyll and creating distinctive, often beautiful patterns in the process.

Many leaf miners are highly specialized on certain species, genera, or families of plants, so knowledge of the host plant's identity along with the visible characteristics of the mine can often support field identification of the miner.

Charley Eiseman (@ceiseman) is the author of Leafminers of North America -- the first reference guide to these species -- and curator of the Leafminers of North America project here on iNaturalist, which I encourage you all to join, but more on that in a moment.

Over the last couple of moths as I've documented leaf miners in south Texas and corresponded with Charley, I've discovered that most of the apparently common leaf miners in south Texas are unknown -- either "known unknowns" or "unknown unknowns." Furthermore, there seem to be ample opportunities to document new plant-insect interactions and significant range extensions of known insect species.

What You Can Do

If you live in or visit south Texas, I encourage you to join the Leafminers of North America project here on iNaturalist and begin documenting leaf miners in the area. Here are some tips:

  • Begin to train your eye to spot the squiggles and patterns leaf miners create on foliage -- you'll get the hang of it fast.
  • Photograph the top and bottom of the leaf, even if you can't see anything on the underside.
  • Get a backlit shot of the leaf if you can.
  • Make sure to document the plant species on which you found the miner as well.
  • Manually add your observations to the Leafminers of North America project, and fill out the host plant species field that pops up when you add your observation to the project.
  • If you have no idea what made the mine, you can enter it as Pterygota (Winged and Once-winged Insects), which is the insect subclass that contains all the mining groups.

Ultimately, a lot of these insects will need to be reared to adulthood and analyzed by specialists to identify them (and, when warranted, name new species). That could be a great project for a Texas Master Naturalist chapter, grad students, etc., particularly so that appropriate permissions and ethics could be assured.

Maybe leaf miners will never have the status of birds or butterflies in south Texas, but what a great opportunity to advance scientific knowledge!

Here are some of my early observations organized by plant family (most of the information noted below comes from discussions with Charley Eiseman).

Plant Family Boraginaceae

There's a moth larvae that lives in the leaves of Anacua (Ehretia anacua). It seems to be a gracillariid moth in the genus Dialectica but the species is unknown.

And on Cordia boissieri (Anacahuita or Mexican Olive), there's a miner that also appears to be Dialectica sp., but it's also unknown. See comments here on a moth reared from Cordia sp. in Florida: https://bugguide.net/node/view/865617/bgpage

Plant Family Malvaceae

In November, I noticed blotch mines all over the Turk's Cap (Malvaviscus arboreus) at Sabal Palm Sanctuary. It turns out no miners are known from Malvaviscus, so this insect is a big mystery. I have been checking Turk's Cap plants ever since at other locations but have not found similar mines.

I found this solitary mine on Malachra capitata at Resaca de la Palma State Park. No miners are known from Malachra, but this appears to be an agromyzid fly.

Plant Family Sapotaceae

These beautiful little mines seem to be common on Coma (Sideroxylon celastrinum) across the Rio Grande Valley, but there's apparently no scientific documentation of a leaf miner on this species. The leading candidate seems to be the moth Parcetopa bumeliella, which is known from other species in genus Sideroxylon.

Plant Family Rhamnaceae

This is one of those "unknown unknowns" -- a small blotch mine on the thin leaves of Condalia hookeri (Brasil or bluewood). @ceiseman's comment on this one was, "Something completely unknown... the only Condalia leafminer I know of is an undescribed nepticulid I found on another Condalia species in Texas."

Plant Family Rutaceae

Sierra Madre Torchwood (Amyris madrensis) can have abundant mines on its leaflets, but the insect species that makes them is unknown.

Recently I've noticed these very tiny mines on Zanthoxylum fagara leaflets (Wild Lime or Lime Pricklyash). This is also an unknown species; Charley Eiseman thinks it may be a moth that mines early in its life and then exits the leaf to continue larval development somewhere else.

This mine on Zanthoxylum hirsutum (Texas Hercules' Club, etc.) at Aransas NWR may represent the first record of the moth Fomoria pteliaeella on this plant species.

Plant Family Asteraceae

This mine, apparently from a Liriomyza fly, was on a dwarfed Texas Palafoxia (Palafoxia texana) plant in a mowed strip adjacent to a parking lot at the South Padre Island Convention Center. And it turns out to be not only the first record of a leaf miner from the genus Palafoxia but one of only two for the tribe Bahieae.

This blotch mine on Blue Boneset (Tamaulipa azurea) is the presumptive first record of a leaf-mining fly (family Agromyzidae) from Tamaulipa.

They fly that makes these linear mines on Mexican Trixis (Trixis inula) is an unknown species.

Plant Family Cactaceae

The moth Marmara opuntiella makes mines (technically stem mines, in this case) on prickly pear pads. I've recorded the species on Opuntia alta and O. gomei in Cameron County, both of which are presumptive new host records for this species.

Plant Family Rubiaceae

I have found two miners on West Indian Milkberry (Chiococca alba). The first is an unknown species of Marmara moth.

The second is apparently an ermine moth called Podiasa chiococcella that has previously been recorded only from Florida.

Plant Family Sapindaceae

This little miner was working on a leaflet of Urvillea ulmacea (Apaac) at Resaca de la Palma State Park. No leaf miners are known from the genus Urvillea, so its identity is a complete mystery.

Plant Family Apocynaceae

While some Liriomyza flies are known to mine milkweed leaves, there are no known species that specifically mine Pearl Milkweed (Matelea reticulata), like this one on the bird blind at Resaca de la Palma State Park.

Plant Family Cannabaceae

This is one of the "known unknowns" -- an unknown species of Stigmella moth that occurs on Celtis pallida (Spiny Hackberry or Granjeño).

Unknown Plant Family

I think I said, "Oh, cool!" out loud when I saw this herringbone-pattern mine, but I haven't been able to figure out the plant species it's on. The plant observation is here: https://www.inaturalist.org/observations/67272345 -- can anyone shed a little light?

I hope this will serve as an inspiration to some and a step toward greater knowledge about these interesting organisms. Thanks to those of you who have been helping with my plant IDs, by the way, which is an important part of this process!

Tagging a few of you who may be interested: @jciv @matushkaelizabethperdomo @bcfl14 @dingooctavious @javigonz @vanwest @gcwarbler @johnyochum @ernest5h @oleanderseth @sambiology @greglasley @maraleemoats @jcochran706 @sa88lebags @joshua_tx @beschwar

Posted by djringer djringer, December 30, 2020 19:55

Comments

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Fascinating stuff! Thanks for tagging me. I'll see if I can make some records.

Posted by jcochran706 about 2 months ago (Flag)
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Thanks for the tag! I'll start taking photos now that I know someone is interested. I see these all over the place, but had no idea if anyone was interested in them, or even what groups make them. You have helped to clear up a bit of that last part! :-)

Posted by beschwar about 2 months ago (Flag)
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Great stuff! I've always been fascinated with leafminers but have been routinely frustrated when trying to either find/document the larva, find a pupa, or rear an adult. 0% success rate so far! This seems like a very specialized skill set to my untrained eye....but I'll give it a try.

p.s. Your unknown plant in the last example above appears to be good (?) old Stinging Nettle.

p.p.s. There is an abundant leafminer on Frostweed that I see every year in my yard but have never pinned down; I've never actually observed the culprit:
https://www.inaturalist.org/observations/19370007
Any clues? @ceiseman ?

Posted by gcwarbler about 2 months ago (Flag)
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Great summary! @gcwarbler the form of the leaf mine strongly suggests the plant is something in Verbenaceae; there's nothing like that known on Urticaceae (but of course, as the rest of @djringer's post illustrates, that doesn't mean it doesn't exist in south Texas!). I left a comment on your frostweed observation. Determining which species of Liriomyza with certainty would require rearing adults, but I'm sure that L. arctii is the one that's abundant in my yard in Massachusetts, on Verbesina as well as Arctium, Heliopsis, and some other Asteraceae.

Posted by ceiseman about 2 months ago (Flag)
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Thank you for tagging me to this post, @djringer ! I will definitely join the project and be on the lookout!

Posted by maraleemoats about 2 months ago (Flag)

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