Serpentine leafminer damage
Photo: University of Wisconsin Extension, Wisconsin Horticulture, retrieved November, 2011. http://hort.uwex.edu/articles/leafminers-vegetables
Citrus Leafminer damage
Photo: Dr. Scot C. Nelson, CTAHR
The leaves of plants have many wandering pale lines.
Leafminer larvae feed in the middle tissue layer of leaves of many different crops, leaving a white or greenish colored trail. The trail meanders all over the leaf. Occasionally you may see black frass.
Generally, we tell people not to worry too much about leafminers. You can remove affected leaves to prevent spread of the pest, but an infestation is never generally enough to kill a plant.
Chemical control: Though there are chemicals available that are effective against leafminers, they do more harm than good by killing parasites of the leafminer.
Kendal Lyon, Hawaii Island Master Gardeners