I have attempted to grow ribes rubrum (Red Currant) for many years in Mt. Shasta, California (elevation 3,500 feet, winter temps occasionally into the low teens) with highly variable results. More recently the yields have dwindled due to some type of insect larva. The initial damage to the fruit is noted as a blemish (dark red) and a slight indentation on the skin of the berry. If left to "mature" the berry dries out some and ultimately falls off. I dissected a berry and found a small, soft sphere containing an off-white larva approximately 3 mm long and
Red Currant: Insect damage to the fruit
Maybe a currant fruit fly?
Another good link