Typically those insects pass through at a particular point and do not continue to cause issues as the season progresses.  One option to limit further damage is to use a systemic fungicide.  There are several companies that make a systemic tree and shrub insecticide.  You can also use product like neem oil or products that have spinosad as the active ingredient. Just keep an eye on the new growth.  It may have just been a 1 time infestation. 

MP