I’ve found these mostly on the underside of my garden leaves. I’m pretty sure that the adult insect looks a lot like a gnat (I’ve bagged leaves with the eggs on them and in the morning I’ll see them); they’re small, black, and winged. Whatever it is, it’s not picky over plants (I’ve found it on my succulents, hydrangeas, inch plants, and volunteer saplings/weeds that pop up).

The thing that’s holding me up is the egg case, which rules out a lot of common gnat-like types. It almost looks like whatever insect lays the eggs right below the surface of the leaf.

I normally wouldn’t be too bothered, but I think these critters are sap-suckers and I find so many new egg cases daily that it’s borderline an infestation. I tried letting nature do nature, then neem oil, then spinosad.

No lines like leafminer, no munching like beetle, the leaf will sometimes become "droopy" when the eggs/larvae are found on it.