Raspberries being decimated by green bottle flies

Is anyone else experiencing a plague of 'green bottle' flies feasting on autumn fruiting raspberries this year?  We've had bumper crops for the last three years in a patch approximately 4m x 4m, and this year's is no exception - the tragedy is that so many of the fruit are being eaten and molested by big green flies (and the occasional wasp). Lots literally half eaten or holed, with others blighted by strange 'hard' grey areas around the stalk.  Any good ideas?  Fine mesh netting seems like a possible solution, but it's a biggish area.