Is the fly problem only recent ? I visted an old finca in september and noticed a lot but I was half expecting it as the olives hadn't been picked for a couple of years, as you say ''left to rot'' , wonder if this is the reason ie, lots of olives still growing but not commercially harvested or maybe its been one of those periods when you get plagues of insects , due to climate/temperature or what ever ? , does the winter get a lot colder in Teruel ?