runner bean-pest or disease?

  I noticed the other day that one runner bean leaf had whitish edging ,but put it down to a bit of heat damage from being on the windowsill.The beans are outside now and this same leaf looks like it has been eaten in patches on the surface just about halfway through.Does anyone know what this might be?

 yes,I have been told off! I had them outside in a little plastic greenhouse but they were getting too hot.These marks look like tracks.

 I have this image of a little insect with a pick over it's shoulder! no,just googled leaf miner and it's not like that...now I wish I hadn't chucked the leaf! the tracks are wider and green,like just the top layer has been taken off.I looked on the RHS site and it said -superficial damage....wait for it...probably caused by insects  hhmmm,helpful.

I will try and rescue the leaf from the recycling bin!

This is the best I can do!