There are apparently dark-winged fungus gnats (Sciaridae) that mine in pelt lichens (Peltigeraceae) in Europe. @nealkelso found linear mines in a Peltigera in Minnesota, but the larva that came out of them turned out to be a midge in the genus Bryophaenocladius (Chironomidae).

The larva is shown in this observation and this one too; so we know larvae are active in July, at least.
Neal has been using a "Lichen Miner" tag to keep track of Peltigera observations that show these mines, and they are all over North America:
https://www.inaturalist.org/observations?verifiable=any&place_id=any&field:Lichen%20Miner=yes
And he has noted a few other examples outside of iNaturalist:
https://www.waysofenlichenment.net/lichens/Peltigera/canina/Peltigera_canina-jason-20090813-57-32%251.jpg
https://www.waysofenlichenment.net/lichens/Peltigera%20canina
So far this midge species is known from just a single larva, and adults are needed to identify it--or describe it if it is new. So if you know where to find Peltigera, please keep an eye out for mines, and if you find them, collect the thalli to try and rear adults! Any larval or pupal remains should be preserved in alcohol along with the adult midges.
It's worth keeping an eye out for mines in other foliose lichens too; I'm told that mines of an unknown insect have been found on Sticta (also Peltigeraceae) in Panama.

Another mystery that needs to be solved by rearing is the identity of the Marmara species on eastern conifers other than white pine. It could be that they are all M. fasciella, but we can't be sure without comparing the adults (or DNA, theoretically). The mines on both fir and hemlock, like those of M. fasciella on white pine, end with an excised bark flap on the underside of which the cocoon is spun (see this blog post to get an idea of what that looks like--also this observation shows it well), so this should be a relatively easy one to rear: just look for the bark flaps in late spring, carefully peel them off without damaging the cocoon (maybe using forceps), and put in vials to wait for adults to emerge.

Here is a mine I found on balsam fir (Abies balsamea) in Vermont:

These mines have also been found on A. balsamea in Maine...
https://www.inaturalist.org/observations/85256161
https://www.inaturalist.org/observations/88855981
New Brunswick...
https://www.inaturalist.org/observations/109767802
https://www.inaturalist.org/observations/110299136
https://www.inaturalist.org/observations/112465983
https://www.inaturalist.org/observations/112465186
Nova Scotia...
https://www.inaturalist.org/observations/116740078
https://www.inaturalist.org/observations/177333514
https://www.inaturalist.org/observations/177333515
https://www.inaturalist.org/observations/181658204
...and Prince Edward Island:
https://www.inaturalist.org/observations/80468907
https://www.inaturalist.org/observations/80318087
https://www.inaturalist.org/observations/80315955
https://www.inaturalist.org/observations/80823460
https://www.inaturalist.org/observations/80872038
https://www.inaturalist.org/observations/80870913
https://www.inaturalist.org/observations/84287251
https://www.inaturalist.org/observations/109427171
https://www.inaturalist.org/observations/203194404
https://www.inaturalist.org/observations/204546152
https://www.inaturalist.org/observations/204739802
https://www.inaturalist.org/observations/210507701

Mines have also been found on nonnative Abies concolor in New York
https://www.inaturalist.org/observations/39616187
and Ontario
https://www.inaturalist.org/observations/84616887
https://www.inaturalist.org/observations/132083669

Mines on Tsuga canadensis were first reported in Massachusetts in 1917. They have also been found in New Brunswick,
https://www.inaturalist.org/observations/110052658
https://www.inaturalist.org/observations/110523210
Nova Scotia,
https://www.inaturalist.org/observations/112555245
https://www.inaturalist.org/observations/116749240
Prince Edward Island,
https://www.inaturalist.org/observations/82228706
https://www.inaturalist.org/observations/110703281
https://www.inaturalist.org/observations/208190876
https://www.inaturalist.org/observations/209745936
Maine,
https://www.inaturalist.org/observations/53518387
https://www.inaturalist.org/observations/170265679
New York,
https://www.inaturalist.org/observations/73777352
Vermont,
https://www.inaturalist.org/observations/201502914
and Pennsylvania
https://www.inaturalist.org/observations/104574273

Normally trees in the cypress family don't have smooth bark that allows you to see mines, but a few mines have been found on Atlantic white cedar (Chamaecyparis thyoides) in Massachusetts,
https://www.inaturalist.org/observations/67570436
on eastern red cedar (Juniperus virginiana) in Massachusetts,
https://www.inaturalist.org/observations/68054967
and on northern white cedar (Thuja occidentalis) in Ontario
https://www.inaturalist.org/observations/68659854
Pupation bark flaps haven't been found on these hosts, so it's conceivable that the larvae exit the mines and wander for a while before spinning cocoons, as is the case with most Marmara species... or maybe they do form bark flaps that just haven't been noticed yet.

This one's a Florida specialty: entirely linear mines on either the upper or lower surface of pond apple (Annona glabra) leaves. This is another one that should be pretty easy to rear, because pupation is within the leaf. I recommend waiting to collect until the pupal chamber has been formed; this is often at the edge of the leaf, where it causes a small fold.

Is it an undescribed species or a new host for one that already has a name, like P. liriodendronella? We won't know until someone rears adults (or, maybe, gets a DNA barcode from a larva). Here are all the observations I've seen of these mines:
https://www.inaturalist.org/observations/40606429
https://www.inaturalist.org/observations/42683330
https://www.inaturalist.org/observations/45007606
https://www.inaturalist.org/observations/45007608
https://www.inaturalist.org/observations/53064418
https://www.inaturalist.org/observations/93788136
https://www.inaturalist.org/observations/172311718
https://www.inaturalist.org/observations/175384725
https://www.inaturalist.org/observations/196317320
https://www.inaturalist.org/observations/201302859
https://www.inaturalist.org/observations/204668219
https://www.inaturalist.org/observations/204937719
https://www.inaturalist.org/observations/204939544