You learn something every day...
Flies are reared in large numbers in Japan to serve as pollinators of sunflowers in greenhouses, especially the maggots. (from Wikipedia).
And I'd just like to add a couple more instances where, whether we like them or not flies have proved useful to our species.
Maggot therapy - Wikipedia, the free encyclopedia
Casu marzu - Wikipedia, the free encyclopedia - for you, Dianne - amazing what they come up with in Italy!