Every year I have this problem and I am sick to death of it.

I love to grow runner, French and broad beans and I am determined that this year I need to do something about the 'bugs' that are getting to my beans. All goes well up until the flowers bloom. I wait patiently for the beans to form and then........disappointment Very few beans to pick. Something is chopping them off before they form so what I have is the stalk which looks like somebody has come up with a pair of scissors and cut the beans off. Last year I sprayed with a bug killer but it didn't work. I will be planting extra plants this year but can somebody tell me what is it that's doing this and also how to stop it PLEASE!!!!