One of my runner beans was wilting badly so I pulled it up and saw lots of small white grubs around the stem. There were no roots left on the plant. I have never had problems with runner bean roots being eaten before.
The grubs were about 3 or 4 mm long (or less than 1/5" for those of us who use proper rulers).
I drowned them in a water butt.
Has anyone else come across this problem? Does anyone know what they are? And, more threateningly, do they have more than one generation in a season?