Larger flies such as carrion and dung flies visit and pollinate pawpaw (Asimina triloba). Many Rosaceous flowers in the northern hemisphere are visited and at least partly pollinated by flower flies (Syrphidae): Apple (Malus domestica) and Pear (Pyrus communis) trees, strawberries (Fragaria vesca, F. x ananassa), Prunus species (cherries, plums, apricot and peach), Sorbus species (e.g. Rowanberry) and most of the Rubus-species (Raspberry, Blackberry, Cloudberry etc.) as well as the wild rose Rosa canina.
I found this interesting as well who would think and apple tree would be pollinated by a fly? The main focus on pollinating is put onto bees which I would think would be logical because they provide another form of food production in the way of honey but to fully understand the nature of pollination I would think it would be important to consider a whole eco system of pollinators.
Anyway, some of the flies look a little like bees so that as they do their work they are less likely to be bothered by predators. One example of this is the Hover Fly.
So now besides the beetles I have to learn to see the flies in the garden under a new light and hold back on the fly swatter. http://diptera.myspecies.info/diptera/content/flies-%E2%80%93pollinators-two-wings Check out this site for more information or use the search term pollinating flies.