I hate to say it, but it sounds like you might be finding spotted wing drosophila maggots in your fruit. SWD is a new pest. Are they small (smaller than a grain of rice) and white?

Where do you live?

I posted a link to the thread I started about SWD a few weeks ago.

Here is a link that might be useful: SWD post

Thank you, fruitgirl, for information.
I live in Washington, near Seattle. From the reading, i see that i got SWD.
I will miss my raspberries if i will not find how to fight fly organically.
I managed to fight currant fly with covering bushes after they finished flowering with a net, but raspberries are not flowering all at the same time, covering can be a problem.

Have you read about usage of used coffee drounds?
I am going to cover soil around my raspberries with coffee ground (thanks to Starbucks) hoping that cofein will kill pupae.

Any thoughts or info on this approach?

A net probably isn't going to work, unless it's a really, really, really fine one. These are "fruit flies" like the kind you get flying around bananas and stuff that you leave sitting on your counter...so, the adults are really tiny! And you'd have to leave the net on when the fruit is ripening, not when they are flowering, as the adult female lays eggs in ripening fruit, not flowers.

I don't know if coffee grounds would be effective, because the larvae can pupate inside the fruit, so the cofein might not ever touch the pupae, especially if the pupae forms and the adult emerges before the fruit drops to the ground.

There is a product made by Dow called GF 120 that is OMRI approved. It's a bait. If you don't want to spray it on your plants, you can put it in a container in your planting. The blog that I linked to in my first post should have some instructions for use of GF 120.

I was using very tight net, actually fabric used to make bride's veils, on my current bushes.
I have read about CF 120 (thanks for link). This might be a plan for next year, but i wanted to try to kill pupae that are currently in soil near raspberry bushes because i failed to collect all fallen berries.
Will try coffee grounds.

It was said "I was using very tight net, actually fabric used to make bride's veils,"

I suspect SWD could get through that. They are half the size of the nuisance fruit flies -- aka vinegar flies -- that hang around your fruit bowls.

Two nice informative blurbs here
http://oregon.gov/ODA/PLANT/IPPM/index.shtml

Here is a link that might be useful: spotted wing Drosophila (SWD)