4 Answers

The fruit flies are coming in to your home on the fruits and vegetables that you are bringing in from the garden, grocery store or farmer's market. It's very common for this to occur during the warm summer weather.
Wash your fruits and vegetables when you bring them into the house. You can use a product like Veggie Wash if you are worried about removing waterproof pesticides. Or, refrigerate them. Either way, you want to remove the breeding source for the flies.
Ripe, soft fruits like bananas, peaches, pineapple and strawberries are some of the most frequent breeding sources for fruit flies. Once you remove the

Fruit fly on bowl
breeding source the fruit flies will be gone within hours. They have a very short life span so you won't see lots of breeding adult flies if they have nothing to eat or nothing to lay their eggs in. http://www.asktheexterminator.com/flies/Where_Do_Fruit_Flies_Come_From.shtml

Read this:  http://www.mnn.com/health/healthy-spaces/questions/where-do-fruit-flies-come-from

'Time fles like an arrow, fruit flies like a banana'.