[bob22]

First thought: move the bananas to the kitchen.
Second thought: you sure they are fruit flies? They really are attracted to fruit mostly (gases they give off). Have you tried pesticides for where you think they are coming from? Tacky fly strips for a week might break the reproductive cycle.

 

[AGWhitehouse]

a bowl of vinegar on the counter next to the fruit has worked for me...they are attracted to it and then get stuck in and drowned in it.