The Purdue Plant and Pest Diagnostic Laboratory

What's Hot at the P&PDL
September 21, 2012

Time flies like the wind; Fruit flies like bananas

Timothy J. Gibb, Extension Entomology, Purdue University

Is it that time of year already?  Summer is gone and Fall is here.  Where does the time go?  An old addage goes something like … ‘time flies like the wind’.  How true it is.  A similar and equally true saying, no doubt coined by some frustrated gardener, goes something like …  ‘fruit flies like bananas.’

Both statements warrant deep reflection but what is their relationship? Gardeners are now proudly bringing their bounties of fruits and vegetables into the home for eating or processing, but in so doing, they often also accidentally introduce a nuisance pest called a fruit or a vinegar fly. These are tiny, brown or black colored flies, about 1/8 inch long that usually have red eyes (if you look really closely).

Fruit flies can be a pest year round, but are especially common during the late summer or Fall because they hang around ripened or fermenting fruits and vegetables, including tomatoes, melons, squash, grapes, apples, peaches or just about any other perishable items brought in from the garden.  They are also equally attracted to rotting bananas, potatoes, onions, and other produce purchased at the grocery store.  Regardless of where they originate, once inside a home, their reproductive potential is enormous.  Given the opportunity, a female can lay about 500 eggs.  An entire life cycle (egg to adult) can be completed in about a week.  This means that 500 flies can mature, mate and reproduce within one week and each female can then lay 500 eggs of her own.  Over just the course of August and September, zillions (got a calculator) of flies can result. 

Fruit flies are primarily nuisance pests.  However, they also have the potential to contaminate food with bacteria and other disease-producing organisms.  They usually infest any over–ripe fruit or vegetable but they also can reproduce in small amounts of fermenting juices that may have spilled behind sinks, cupboards, clogged drains or garbage disposals or in dirty trashcans.  In fact, they can even breed in empty bottles and cans, or even mops and cleaning rags.  All that is needed for development is a moist film of fermenting material.

The best way to avoid problems with fruit flies is to eliminate sources of attraction.  Produce that has ripened should be eaten, discarded, refrigerated or processed.   Do not leave it sitting out on the cupboard for an extended length of time.

Once a home is infested with fruit flies, all potential breeding areas must be located and eliminated.  Unless the breeding sites are removed or cleaned, the problem will continue no matter how often insecticides are applied to control the adults.  Finding the source(s) of attraction and breeding can be very challenging, and will require persistence on the part of the home-owner.

After the source of attraction/breeding is eliminated, homeowners may want a solution for the pesky swarm of flies that continue to hover in the kitchen.  Several options may help. 

  1. A vacuum cleaner can suck them up quite readily.  Even a dust buster in the hands of a determined homeowner is bad news for fruit flies. 

  2. Home made fruit fly traps consisting of a cup of apple cider vinegar and a teaspoon of dish soap in an open dish can be effective when placed near where the swarms persist.  Fruit flies become attracted to the smell of the vinegar, (why they are often called vinegar flies) and will attempt to land in the bowl but because of the soap, the surface tension of the vinegar is reduced and the unsuspecting fruit flies drown in the mixture.

Always remember that ripe fruits and vegetables plus even a short period of time equals fruit flies.  It is basic entomological mathematics.  It can also be stated as, ‘time flies like the wind and fruit flies like bananas.’

Click image to enlarge

Fruit flies congregating on open watermelon

Fruit fly maggots in rotting produce
(note the tiny size of the young maggots next to the pencil)

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service