We see a little insect feeding and some possible fungal spotting, but not enough to kill a tree, or even explain a great deal of leaf loss.
We suspect that the leaf drop is not insect or disease related. It is now late in the growing season and many plants are looking beat up. We have had severe drought in some areas and high temperatures. If you have had little rain (even if you've had 1-2" lately if does not make up for a month without rain in high heat), consider watering the tree. Place a hose on a low stream under the tree and move it about periodically after it has soaked deeply in one spot. Water the area from the drip line (edge of leaf canopy) inwards to the trunk.
Be alert for a fall drought--they can be killers.