Help !! Chafer grubs are killing my young trees !!

Hello permies !

I've complained elsewhere on this forum about the serious damage that voles have been inflicting on my trees.

This year, a new pest is causing us additional trouble: the chafer grub https://en.wikipedia.org/wiki/Cockchafer

For the last couple of years I have been planting my trees in wire nets in order to protect their roots from voles. And indeed, the wire mesh is doing a decent job in keeping the roots safe from the rodents.  

Sadly, the mesh provides no protection from chafer grubs, which come up towards the surface from deep below and reach the tree's roots through the opening at the bottom of the mesh.  They eat all the fibrous roots, and the cambium on the taproots.  Unlike in cases of vole attacks, the stricken tree remains well anchored in the soil, as there is still a lot of woody root to keep it anchored, but it's showing evident signs of stress (yellowing / loss of foliage, stunted growth).

Any ideas / suggestions on how to deal with this pest would be greatly appreciated !