Black mite (?) on pear bark.

Hello. I've just moved house, and live on the Yorkshire coast. I have a young pear tree in my garden, which has been rather roughly pruned, and is suffering. I've found a host of tiny culprits, perhaps mites, but can't identify them - can you help? The creatures are tiny - less than half a millimetre (as shown on the attached photograph, which is the best I could get). They seem to be a glossy black colour, with eight legs not obviously of a different colour. They congregate at the base of branches and the remains of branches; and there must be hundreds, overall. I assume they are sucking sap - which is producing weak, yellow and patched leaves. I've ordered some Neem oil, which apparently may help. I really don't want to use any chemical insecticides. I'd like to be sure what I'm dealing with, so any help in identifying these tiny monsters would be appreciated.