Those twisty trails you described are called leafminers. They are the larva or maggots of a certain type of moth, fly or beetle. They tunnel between the top and bottom leaf egdes, and the destruction they caused can cause young plants to be severely stunted or create lower yeilds in older plants. They are PAINS IN THE ASSES!! The neem oil will discourage the adults from biting into leaf or laying eggs under leaves, but not guarenteed to prevent. Best method I have found is physically removing larva from leaf with tweezers (look for a slightly orange bump in the trail) and spraying with neem oil and then using row covers or netting to prevent them from returning. They are notoriously hard to get rid of, and another method you may use is distracting them with other plants they like, say like eggplant, lambshank, or columbine. Even basil or celery plants, which they supposedly love will do the trick. So will sticky fly tape near plants, perferably the color yellow, to which these suckers are drawn. Good luck.
