Different species of leafminers feed upon different plants. Leafminers may be either a wasp, fly, moth or beetle species.
Adult leafminers puncture holes in the leaves as they lay eggs. Look for white specks from these egg laying punctures in the photo. As the larvae feed, winding (serpentine) mines develop as seen in the photo. Leafminer larvae are protected as they feed between the upper and lower leaves making control difficult. If only a few plants are affected, remove infested plants. Once larvae are inside the mines, insecticides with systemic or slightly systemic (translaminar) activity work best.
For more information on management see: New England Greenhouse Pest Management Guide