You are right, David. When I looked more closely, I did find leaves indicating that the damage is caused by larvae of chafers, and between two leaves stuck together with a fine web, I detected this larvae (top photo). It was about 7-8 mm long, pale, small head, very short legs. It didn’t like to be disturbed and was moving very rapidly, so it was difficult to get a proper photo of it. The next shows the leave where I found it, and the last one of a leaf in an advanced stage. At the end only the nerves are left.
I don’t see the adult chafers on the roses now, but there are plenty of large, green metallic looking chafers having a feast in our pear tree.
_7031845_Offending larva.jpg by
JorunT, on Flickr
_7031859_Early leaf damage.jpg by
JorunT, on Flickr
_7031860_Advanced leaf damage.jpg by
JorunT, on Flickr