I am going though all the posts of Pegomya solennis.
I believe it unwise to agree to pictures of mines in plant tissue without fairly strong supporting evidence. Whilst I think there is a very good chance that you are right here, it is still only a chance. I note that Joe feels comfortable and I respect that.
I usually go through other posts of these (obscure) observations - there are never many in Other Observations. I feel compelled to offer comment and be generally supportive and encouraging whenever possible.
For my post of today I looked at every other one in iSpot - a useful exercise.
Now see http://www.ispotnature.org/node/817566
Lat/Lng: 52.0, -0.7
OS grid ref: SP8936