brussel sprouts and the blessed cabbage white/caterpillars

Ok, so I have netted the sprouts a while ago after clearing what I could see of the caterpillars and spraying the rest somewhat. Of course some remained and have become cabbage whites in the netting which I remove on a daily basis. And so the cycle will continue I am sure.

However, although the outer and top leaves are nibbled quite a lot, many sprouts have started to "bud", even on the most nibbled sprout plants. My question is, what else can I do about these little blighters to ensure I don't have a zero crop of sprouts. If indeed anything can be done.

At least the birds cannot get anywhere near the sprouts. 

the holes are 7mm and I could not see any joins at the posts and the ground. I guess there were caterpillars I didnt squish when I put the netting over that grew into the butterflies. I can only hope that the sprouts will not be decimated.