Please can anyone identify this beetle. It is shiny dark blue in colour almost black, approx 5 - 6mm in size. The beetles decimated a line of trees at the side of our house last year by eating all the leaves. I'd hoped the winter would have killed them off, but doing some gardening today I found them in the soil alive. I don't know whether these are last years beetles or whether eggs have been laid and they've hatched. I would like to find out what they are and try some pesticide on them - if anyone has any recommendations that would be great.
It belongs to Chrysomelidae. At a quick glance (hey, it's Friday evening!) it looks not too unlike an Alder Beetle (Agelastica alni). Compare this. It lives on alder, but can occasionally be found on other trees. Cheers!