Hi,
The aroma of sweet smelling juices or food can sometimes be such a significant draw factor that it is almost impossible for "Electric Fly Killers" to work effectively enough to bring the numbers down.
In a particular factory, a proposal to built a top-down light mild steel gate with boogies on a single rail track was built to surround the main open area of the factory. It also had "removable" of 4" x 4" panels that were made of aluminium strengthened with micron-mesh size to block off any entry of flies.
After the gate was put up, analytical evidence from electric fly killer indicated substantial reduction of fly population.
The surrounding compound of the factory had a good clean up with zero presence of food, stains and /or if any present, were immediately removed by the end of the day or perhaps in some cases, on a continual survellance basis.
Not only do you need the support of a good Pest Contractor, internal Good Sanitation Policies and Practices obviously play a major role in determining the level of success in a Pest Control Program.
Each and every pest situation can be very demanding in it's own ways and may call for a dynamic solution to gain effective control over these pests.
There is simply no fix-it-all solution and the above is again just another example of a situation that had to be handled in the manner that was thought ideal.
All the best.