One of the sellers I bought from last season gifted me with leaf miners, and I ended up with a pretty bad infestation. When I posted here about it I was told that they would overwinter. (I truly didn't think that would happen this far north!)
This psychotic weather, polar vortex and all, has presented us with an extended period of sub-zero temperatures, at times dipping to -18 F. We've had brief periods of snow cover until recently, and cover for the past week or so.

Would this possibly be enough to kill off the leaf miner larva currently hiding in my daylilies?

The daylily leafminer was first recorded in Maine, so I would not be too hopeful about winter killing it in Ohio.

Where does it overwinter on dormant daylilies whose leaves have all dried up? In the soil? I used to get the occasional leaf miner here, but these last few years they seem to have doubled. I read there is a newer species/import of daylily leaf miner that is worse then the old one, but don't know if that's true or what is happening...........Maryl

It spends the winter as a pupa in the base of the old leaves. Ophiomyia kwansonis is a new species to North America, it is of Asian origin and specific to daylilies. It's only been known in North America since the mid-2000s.

Thanks Sooby. Does it infect other plants? I ask as I grow 95% of my daylilies in pots which every spring I freshen with root pruning and new potting mix. Depending on where the larvae reside on the root (as in right next to the crown itself) you'd think that I would have less of a problem then most. Also, plants from northern growers (from whom I buy almost exclusively) come bare root. I'm thinking this leaf miner is perhaps less specific then just daylilies?? as it's spreading nationwide? They really are becoming annoying.......Maryl

They pupate in the mines in the leaves not the root. No it doesn't infect other plants, only daylilies, but there are many other kinds of leafminers that affect other plants.