It is a specific fruit wasp that is killing my gooseberry and I posted on the fruit forum and they suggested Sevin - so BT was the kinder alternative. I have lost almost all my fruit and parts of the bush. :(
If you're going after "worms" you'll want to get Bt "kurstaki" variety. The liquid form, as catmad said, is known as Thuricide. The powdered form is sold as Dipel. Both products are usually available and the box stores, garden centers, etc.
I doubt the wasps are giving you troubles, usually any wasp around gooseberries are predator wasps, eating "bad" bugs. I think you're being plagued with gooseberry fruitworm, or perhaps current worms, both of which can be controlled with Bt (or Sevin, if you choose). Anything you see flying around that resembles a fly is the adult form, a moth, not a wasp.
Even though you may have lost most of your fruit I'd recommend going ahead and dust or spray to zap any stragglers that will grow into adults, starting the life cycle all over again.
The person helping me did say worm - I'm easily confused. Thank you so much, Shoe. I will go to the Big Box on my lunch hour with your list. How long do I have to wait to pick the gooseberries after I dust them - I want to make jam.
There won't be a waiting period with Bt, it doesn't harm warm-blooded animals (us!) nor does it have an secondary or tertiary effects (for example if an infected worm is eaten by a bird the bird is not affected).
If you have any ripe fruit I'd pick it then spray or dust the plants. You can store whatever you pick in the freezer until you can pick more and get enough for jam and such and it won't affect the texture or flavor of the jam.
Whew...my tomato sammich is gone so back out to work I go!