Sure enough, there they were, sawfly larvae munching the pine needles (European critters feasting on a European tree--if only it always worked out this way). Last year was a bumper year for this critter on this particular tree. I got rid of a lot of them with soapy water, and pruned away about half of the tree to reduce the number of denuded branches, but enough survived, or perhaps came from away, to produce a new crop.
There aren't too many this year, and they came later than they did for my many sawfly-mugo pine visitors (though about the same time as last year, judging by their size), but they must go. The tree looks weird enough now from the pruning it got last year--I don't want to put it through that again.