It is leaf miners. They are not trails ON but instead INSIDE the leaves. A very small moth like bug lays eggs on the leaf and the resulting maggot burrows inside feeding on the leaf and leaving the trails. Because they are inside the leaf external pesticide does no good once it is inside. If it is a non bearing tree you can use bayer tree and shrub to kill them...or you can ignore them as the leaf is still producing energy or you can spray something like spinosad weekly to leave a residule film on the leaf that will kill the maggot when it hatches from the egg.

The miners just go after new growth and the first spring flush is normally free of miners. They are a Pain.....

Leafminer, most citrus have these critters, especially in the Deep South. Find something that has spinosad in it and spray whenever new leaves flush.

Thanks! I'm going try out this spinosad. My trees are not blooming, I'm hoping this is the problem.

Oh I guarantee the picture you showed is miners, they are very common. If you look on the very new leaves that just have a short trail you will be able to see the lil maggot and just squish them. I have 18 citrus trees and some seem to be more attractive to the miners than others but except on the very young trees I just ignore them.