Those are likely spotted wing drosophila (SWD; Drosophila suzukii) larvae, an invasive vinegar (fruit) fly which infests ripe and ripening fruit. If your fruit are overripe they could be any species of Drosophila or Tephritid. SWD are the subject of a lot of management research at the moment. I realize my response is several months late but for future seasons, planning is key. Management requires regular insecticide applications (I will have a paper out soon on swd management in blackberry in the SE US), frequent harvest, and often good post-harvest management. We've found that cold storage is quite effective for halting development and/or killing young larvae in berries. There is also research being done of incorporating cultural controls for management in caneberry and blueberries (preliminary info can be found here: http://eorganic.info/spottedwingorganic).