Minix, If possible..........return to this site or customer's home during the early evening or in the early morning and look at the insect that is feeding on these leaves. Cooler times or when the outside heated temperatures are low is the best time to investigate for the vector. Could be Leaf Skeletonizers, Tent Caterpillars,etc. Beetles and Inchworms do the most damage to ornamental trees in the urban setting. The beetles will feed at night while the caterpillar will feed early when the temps are lower.