By the way, I think I forgot to say, I started off manually removing the pests but they were breeding faster than I could keep up with them. Then my wife found a spinosad-containing insecticide she used for some box trees (I think they are called) and it was also recommended for potato bugs. It is supposed to be organic. After I applied this, the bugs completely disappeared (about two days later). The product is absorbed by the leaves.
My fellow gardener (who I hardly ever see because she goes there during the daytime and I like to go there later in the day when it's cooler) used some white powder as soon as her potatoes emerged (I think that is where the plague must have started - she could have left a note to tell me!) and once again when the main crop appeared but I can still see one or two bugs on her main crop potato leaves even now.
The insecticide solved the problem in my case. I have quite a decent harvest (potatoes a bit smaller, perhaps owing to cold start to the season then a drought and then the bugs).
I am a bit fearful for next year as apparently the pest tend to build up resistance!
Anton
