What are these white bugs under my beech’s leaves?

Question

These appeared last year and resulted to premature discolouration and loss of leaves. It seem they have overwintered and going to cause a damage this year as well.

What are they, and most importantly, how do I get rid of them?

I tried neem oil last year, as well as pressured water, but none seems to affect them much.

Answer 1

These are wooly beech aphids and according to RHS they don’t pose any threat to the plant, although they may be a nuisance to the gardener.

RHS considers them as a healthy part of the ecosystem and doesn’t recommend countering them.