Was it me or an infest that's causing damage to the tree?

I've uploaded a few photos to show my concern.

This tree (Elderflower?) seems to have been totally infested with something (insect larvae?) and can now see the tree is wilting. The tree also seems to be keeping the lawn below moist thus encouraging moss and depositing a waxy coating on the slate chips below. You should be able to see the difference between two areas of slate chips. I don't know if this is simply normal and expected.

However, when I took the photos of the infestation which was about 12 days ago, I also used weed killer to kill the grass along the wall and next to the tree. I'm now worried that it was my total ignorance that has caused the wilting.

Can you tell what's going on and what action I need to take if any?

Thanks very much and hope you can help.

 

Great!
Thanks very much.