From what I'm observing and reading about others observations here, I'm thinking these worm/flys are pretty localized. My White Currant and Jostaberry that have been ravaged the last three years anyway are within 10 feet of each other while another Josta  40-50' away had just a few worms this year for the first time that I have seen. I guess if you're eating good, there's not much reason to travel 

I am wondering about the life cycle, or rather generations of hatch and fly to lay eggs/come worms. I visited the mechanical destruction of severe worm population very comprehensively onetime and then again, I want to say maybe a little less than a week (maybe a little more), not as severe an infestation but substantial none the less. This last week I have seen no new worms to smush and my currant and Jostaberry still have leaves.

I'm wondering if this means the generational aspects are evolved to a limited timeframe. If the early worms get all the leaf, later successions will have nothing to eat, so maybe no later successions are normal. Here's hoping.

And worms population should decrease next season if there was as severe a curtailment of the population as I was aiming for; nobody to drop and pupate. With only a few bushes I think this can be managed by hand. While being somewhat gross in the beginning, wearing gloves helped.The learning curve was brief. Don't shake the branches too much, escapees will drop to perhaps repopulate. The followup squish fest for the later egg hatch was gloveless as happens, but abbreviated compared to the initial onslaught.  With just a few plants it seems quite do-able. I'm thinking cultivation of the topsoil a couple times during the growing season to disturb and expose to predators the pupate (if that's the word for what these worms do). The worms proper must taste really bad to birds 'cause they'd be hard to miss...

added at edit:

Gaaahhh!  I Just remembered.... My bushes are not in optimal growing conditions, largely unwatered and shaded on a pitched slope, and so remain small in comparison to a red current (4'x4')  that I moved away from some thirty years ago. So in this context- the robust currant bushes will be a lot more to contend with than my 1.5'x 1.5' currant and  9 stemmed jostaberry.   Not wishing to serve up false hopes or unrealistic expectations. Mechanical control in my case is entirely a possibility, your milage may vary.