I just put together a blog post explaining this, in case anyone's interested: https://bugtracks.wordpress.com/2022/11/13/can-gall-midges-be-leafminers/

Here's a mystery I've been trying to solve for a decade now: a long, linear leaf mine of an agromyzid fly on Adenocaulon bicolor in the Pacific Northwest. It should be a relatively easy one to rear, since the puparium is formed in the leaf (hidden on the lower surface) and there are apparently at least two generations per year, with mines present from June to October.

@jmole, WA, 6/9/2021

@lumenal, OR, 7/6/2021

@lumenal, OR, 7/12/2022

@lumenal, OR, 7/18/2022

@flammulated, OR, 7/22/2021

@flammulated, OR, 7/30/2021

@brnhn, WA, 8/18/2022

@kurtsteinbach, WA, 8/30/2021

@brnhn, OR, 9/5/2021

@johndreynolds, BC, 9/18/2020

Here's another one I'm really hoping someone can collect and rear. The South African moth Digitivalva delaireae is being considered as a potential biological control agent for Cape-ivy in California and Oregon, but meanwhile people have been regularly observing some native(?) leafminer on this plant, and no one knows what it is. There is typically a roughly circular brown spot at the beginning, where the mine is apparently contorted or forms a tight spiral, and this suggests to me that the fly is something other than just one of the polyphagous Liriomyza species that are common in southern California. Although mines have been observed in just about every month of the year, the only one with a larva inside was found on April 11 in Marin County.

@thetorterra, Santa Cruz Co., 1/16/2022

@manidae, Los Angeles Co., 3/28/2020

@marionanoiram, Marin Co., 4/11/2016 [larva present]

@nealkelso, San Francisco Co., 4/24/2021

@garth_harwood, San Mateo Co., 6/4/2020

@sea-kangaroo & @leslie_flint, San Mateo Co., 6/16/2019

@silversea_starsong, Orange Co., 7/4/2021

@ctrubo, Los Angeles Co., 7/18/2022

@cynestor, Santa Barbara Co., 7/23/2022

@dlbowls, San Luis Obispo Co., 8/9/2021

@cynestor, Ventura Co., 8/27/2022

@esppim, San Francisco Co., 8/31/2021

@sea-kangaroo, Monterey Co., 9/18/2021

@danieldas, San Francisco Co., 9/19/2021

@gyrrlfalcon, San Mateo Co., 10/16/2019

@conormcmahon, Santa Barbara Co., 10/18/2021

@bugornot, Orange Co., 11/2/2020

@nealkelso, San Francisco Co., 11/8/2020

@nealkelso, San Francisco Co., 11/16/2020

@nealkelso, San Francisco Co., 11/17/2021

@wxynez, Los Angeles Co., 12/1/2021

@thetorterra, Santa Cruz Co., 12/6/2021

@jon_sullivan, Monterey Co., 12/30/2018

Another commonly observed mystery leafminer that I'm hoping someone can collect and rear: An Ophiomyia species (Agromyzidae) that forms winding linear mines on Lantana camara, L. x hybrida, and maybe other Lantana spp., in California, Texas, Mississippi, Alabama, and Florida. The well-known species O. camarae makes a mine based on the midrib, with short extensions into the blade along either side:
@silversea_starsong, Mission, TX, 11/5/2021
The mystery mines are not based on the midrib, although they sometimes have similar short branches where they encounter lateral veins. It's conceivable that they are made by the same species, but adults need to be reared to confirm this.
@susanhewitt, Carlsbad, CA, 10/1/2019
@dan_johnson, Houston, TX, 10/6/2019
@kimberlietx, Southlake, TX, 6/16/2020 (note long lower-surface portion in this example)
@victorengel, Austin, TX, 7/2/2020
@silversea_starsong, Newport Beach, CA, 7/15/2020 (another example with a long lower-surface portion)
@silversea_starsong, Garden Grove, CA, 10/26/2020
@wsweet321, Long Beach, CA, 11/1/2020
@terit, Natchez, MS, 11/15/2020
@wsweet321, Long Beach, CA, 1/24/2021
@sessilefielder, Los Angeles Co., CA, 1/2021
@chalon9, El Cajon, CA, 7/23/2021
@joemdo, Medley, FL, 7/26/2021 (this one has a distinct frass line and may have been made by a different species)
@silversea_starsong, Orange, CA, 8/23/2021 (the first example follows the lateral veins a lot)
@biocowboy, Long Beach, CA, 8/24/2021
@wsweet321, Long Beach, CA, 9/16/2021
@milliebasden, San Diego, CA, 9/28/2021
@vcharny, Dauphin Island, AL, 10/11/2021
@silversea_starsong, Mission, TX, 11/5/2021
@sessilefielder, Los Angeles, CA, 3/13/2022

This is the first in what I expect to be a series of posts highlighting commonly observed mystery leaf mines. My hope is that people will keep an eye out for them and collect any occupied ones so that adult insects can be reared and we can put names to them. You can click on any of the images below to get to the original observations. These are all mines of some unknown agromyzid fly on Pacific hound's tongue (Adelinia grande); they have been found in several California counties. Empty mines have been found as early as March 9; no one has yet found ones that clearly have larvae inside, although some photos taken in late May show small and fresh-looking mines, so there may be two generations per year.

@sea-kangaroo, San Mateo Co., CA, 3/9/2018, 5/29/2019, 6/10/2020


@temminicki, San Mateo Co., CA, 3/11/2018


@merav, Santa Clara Co., CA, 3/14/2021


@debkccb, San Mateo Co., CA, 3/15/2020


@u_phantasticus, San Mateo Co., CA, 3/20/2020


@chloe_and_trevor, Marin Co., CA, 3/31/2021, 4/22/2021


@cmaci, San Mateo Co., CA, 4/4/2020


@zufi, San Mateo Co., CA, 4/9/2021


@selwynq, San Mateo Co., CA, 4/11/2021


@elonicera, Santa Clara Co., CA, 4/14/2021


@melanopygus, Marin Co., CA, 4/29/2018


@leslie_flint, San Mateo Co., CA, 4/30/2021, 5/4/2020


@gyrrlfalcon, San Mateo Co., CA, 4/16/2021, 5/4/2020, 6/5/2020


@leptonia, Santa Cruz Co., CA, 5/10/2017


@owicki, Santa Clara Co., CA, 5/11/2020


@kzias, San Mateo Co., CA, 5/24/2020


@hoechsle, Santa Cruz Co., CA, 5/30/2019


@calloohcallay, San Mateo Co., CA, 5/30/2020


Update, 3/11/2022: People have found some occupied mines in 2022!


@gina-barton, Santa Clara Co., CA, 3/5/2022


Having seen this puparium that @nancyasquith got from one of these mines (Santa Clara Co., CA, 3/10/2022), I'm now reasonably sure this is an Agromyza species.

Hi everyone,

In the interest of making leafminer identification more accessible, you can now get the first edition of the Leafminers of North America e-book for as little as $5 US. For details, see today's BugTracks post.

Charley

On Thursday evenings from April 29 to May 27 I'll be offering a "Leaf & Stem Mining Insects of the Southern USA" online seminar. "Southern" is anywhere that spring is far enough along for there to be plenty of leaf mines to observe! Details here.

Hello again,

I'm offering a 5-part interactive online seminar on identifying North American leafminers, on Saturday evenings starting July 25. For details see https://www.eaglehill.us/programs/sems-online/calendar-online.shtml

Hope some of you can make it!

Charley

Until further notice, I am offering a free subscription to the 2nd edition of Leafminers of North America to anyone who sends me material of western grape Phyllocnistis suitable for DNA barcoding (i.e., larvae, pupae, or reared adults; not just empty mines--but a mine with a dead, dried larva inside may work). I'm after the mines with the distinct narrow central frass line, like this one:
https://www.inaturalist.org/observations/3900879
So far they have been found in California, Utah, Colorado, and Arizona (in one case on Parthenocissus, which I'd happily accept too). Although this mine type is my primary target, I'll accept western examples of Phyllocnistis vitegenella (the "snail trail" one) for now too. By western I mean west of the Great Plains.

And so people east of the Rockies don't feel left out, I'll also extend this offer to anyone who can collect mines containing larvae (dead or alive) of the mysterious nepticulid moth on dogwood (Cornus spp.). The mines are entirely linear and look much like those of Phytomyza agromyzina at first glance, but the frass is in a central line rather than alternating along the sides, the larva will have a distinct head capsule, and there will be a tiny, shining eggshell at the beginning of the mine (possibly on the lower leaf surface). I don't think I've seen any examples on iNat yet, but empty mines have been found in Ontario, Iowa, Ohio, and Vermont. Here is one I found in southern Ohio on August 6 a few years ago. That's my only datapoint as far as when an occupied mine can be found; the few other examples have been found later in the season, already empty.

If you think you've got what I'm looking for, post the observation and message me!

Hi everyone,

Here's a link to register for a leafminer webinar I'm presenting on Wednesday evening: https://us02web.zoom.us/webinar/register/WN_tOA3peW6TB6JUzQBJ_fImQ
Hope to see you there!

Charley