I looked , and couldn't find the answer
Here are more things to look out for .
They may just form insect galls , on the leaves, and not cause much damage.
If it was bad it Might of been listed here
Looks like maybe it could be aphids
On a side note I eat apples all the time with sooty blotch
at first I thought it was pollution , but now I know
(ugly apples actually have more antioxidants the tree fights off the bugs , and the apples are healthier (I have a link)
I would destroy the leaves though after they fall or dump them some place
https://plantvillage.psu.edu/topics/apple/infos