It is an acalyptrate fly. I was considering Agromyyzidae from your description of behavior but it appears to have a separate Sc vein. Cannot see many of the details needed from the images. Would you be able to use a key to Families such as this one: http://anic.ento.csiro.au/insectfamilies/key.aspx?OrderID=26547&PageID=identify&KeyID=10 (and linked below)  That then would give us a lead as to whom this should be sent...

http://anic.ento.csiro.au/insectfamilies/key.aspx?OrderID=26547&PageID=identify&KeyID=10

Thanks Christine. And sorry, the images are not great. It does have calypters.  I had posted images on the BugGuide and it was also suggested it was in the Anthomyiidae. My rearing chamber has yielded an entirely different actor... The real culprit.

Dear William,

I am not so good taxonomist in Diptera Orders but about my experience and the poor details that I can see it seems to me to be from Agromyzidae family because species from Anthomyiidae are not live inside of stem

Thanks Manole. I'll take some better images and then perhaps the ID can be determined.

Ok, hope to be better

Traian

well if it has calypters that is a completely different story. Anthomyiidae makes more sense. Have you considered a species of Delia, cosmopolitan pests whose larvae are known to damage many plants? Delia echinata stem mine according to the link below... and there are 3 species at least in America that mine in stems according to the second link.

http://www.ukflymines.co.uk/Flies/Delia_echinata.php

http://www.sel.barc.usda.gov/diptera/people/FCT_pdf/Dahlem_FCT.pdf

Update: After a collection of infested stems and rearing of the larva, I determined that the stem borer was a different actor and NOT the insect I initially believed. See attached images. The insect is about 5-6mm long.