Don't let those darn Fruit Flies take over you bar!  Give them an inch and they will take a mile!  There is a lot you can do to prevent them from flourishing.  Here's some things you can do:
No standing water, anywhere!
All drains including floor - sanitizer
Plug beer taps
Clean and plug beer drip tray
Rinse and store empty beer bottles
Cover liquor bottles
Wipe down bottles
Clean soda gun
Bar mats must be clean
Keep garnishes covered and cold.  Wash fruit before cutting.
Don’t be surprised if fruit flies feed on the residue remaining on damp mops, moist cleaning rags and sponges, or near buckets of wastewater.
Bottom of trash cans?
Last resort - traps