-
From its head shape hat looks like some kind of weevil. But from my (limited) knowledge, there are several types of the blighters that look similar - green immigrant leaf weevil? (waits for Daily Mail comments section...)
No idea about killing them off, sorry.
Try here for ID, if you're inclined: http://www.eakringbirds.com/eakringbirds6/insectsphyllobiusweevils.htm - no treatment info either though
What's this? How do I stop it eating the leaves on a small tree which I would like to encourage?
I don't know what sort of tree but it's more interesting than the other stuff that pops up here.