There are two types of agromyzid mines that are very commonly observed, and it would be fantastic if people could rear as many adults as possible to clarify taxonomy.

On Cornus spp. (dogwoods and bunchberries), there are the linear mines identified as Phytomyza agromyzina . The problem is that I have reared another species, P. notopleuralis , from identical mines. Its host was previously unknown, and the few known adults are very similar to P. agromyzina . I suspect that if more specimens can be reared, there will be intermediate individuals--or maybe even mixed batches of both "species" from the same collections of mines--which will allow us to synonymize P. notopleuralis with P. agromyzina . Alternatively, additional specimens could solidify the status of P. notopleuralis as a distinct species, in which case we'd have to identify these mines only to species group/complex level, at least in areas where both species are known to occur.

There is a similar situation with the linear mines on Symphyotrichum asters with frass in large, widely spaced lumps, which we have been identifying as Ophiomyia parda . Another species that was described from a single specimen with unknown larval biology, O. quinta , turns out to make identical mines. As with the dogwood miners, these two species are very similar and my hope is that additional specimens will show they are really two points in a continuum of forms, which will allow us to synonymize O. parda with O. quinta (a little bit sad since the type specimen of O. parda came from my front yard!).
If you click on the link above, you'll see that " O. parda " is strictly eastern, with the exception of one outlier in eastern British Columbia. A few somewhat similar mines have also been found in California, which very likely represent a related but distinct, undescribed species: one that @silversea_starsong found on S. bracteolatum , and one that @chilipossum found on "aster" .
In Florida, similar mines have also been found on Ampelaster carolinianus . These could be another new species, or maybe they are the same as O. parda/quinta ; we won't know until some adults are reared.

Some notes about rearing these: the dogwood-mining Phytomyza species typically exit their mines to pupate, but sometimes the puparium is formed at the end of the mine. The Ophiomyia species on Asteraceae all pupate within the leaf, but the puparium is hidden on the underside (typically right at the edge), so the completed mine appears empty when viewed from above. less ↑