Naughty little bugger, which undermines the harvest of hazelnuts. This tiny little spider does a lot of damage.
Filbert mite
Mites in hazel buds
Very quickly, cut the affected branches and burn them. This is what you will see written often.
In my garden I let things happen; every year, some hazelnut trees are attacked but I still eat hazelnuts. The auxiliaries must surely do their job.
But the hazel tree knows a lot of parasites! Everything you want to know about the entomological fauna of the hazel tree, on the following link:
http://www7.inra.fr/opie-insecticides/pdf/i86coutin.pdf