If you spray with provado bugclear this will kill of these pests and your acer will be ok and in future spray aprox four times a year, once sprayed it is taken in by the plant and prevents further attacks, think it protects for up to twelve weeks but it is very good, your leaves are going to look a little rough but autumns nearly here so dont worry and next year it should leaf up fine just follow the above procedure, most d.i.y outlets sell bugclear in the garden section.