Answer: Lots of different insects feed on foliage and most trees can tolerate the holes left behind. There are some insect specific pesticides, but without knowing which insects you're dealing with, I can't really make a recommendation. You can go out at different times of the day to see if you can catch the culprits in action, but usually by the time you notice the holes in the leaves, the insect is already gone from the garden. I wouldn't worry too much about the holes in the leaves. All except citrus tress will drop their leaves soon; citrus are evergreens. However, broadleaf evergreens such as citrus trees will shed their oldest leaves when they have been on the tree for 2-3 years. So, the holey leaves will remain on the tree for a while but they should not affect the tree's health.
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