Fruit Flies

A small swarm of tiny flies goes airborne when you grab a banana and it seems like you can never quite get rid of them. What are these tiny pests and how can they impact your garden?

Let me start by saying that there is far more to these fruit flies than meets the eye. What started out as a simple post about a common garden/household pest has led me down rabbit holes I never knew existed.

First, fruit flies do not actually eat fruit. Instead, they are attracted to overripe, fermenting fruit, where they can find the yeast bacteria that they do eat. Like other fly species, they lay eggs near favorite foods, which then hatch into larva, or maggots. While fruit flies will not hurt you, they are not something you want in your food, or your garden. Let’s find out why.

Fruit fly life cycle

These tiny pests often take a ride into your home on store bought produce, usually as eggs or pupae. Fruit flies thrive when there is humidity and temperatures of 80° to 89°F, much like the inside of your kitchen. Anything above 105°F will kill fruit flies in a matter minutes and cold temperatures have a similar effect. In spring or fall, however, a single female fruit fly may lay up to 700 eggs in her 25- to 30-day life. What’s worse, when she lays an egg, she coats it with her feces (poop)! This transfers a beneficial bacteria to future generations. These poop-covered offspring hatch 12 to 15 hours later and feed for a few days on your kitchen or garden produce, molting twice in the process. Once these maggots have eaten their fill, they enter a pupal stage that lasts only a few days. This means that each egg becomes a sexually mature fruit fly in about a week!

Drosophila fruit fly feeding off a banana (Sanjay Acharya) CC BY-SA 4.0

Fruit fly description

There are actually thousands of different fruit fly species around the world. Most of them are less than 0.12 inches long, brown or yellow, with red eyes. The legless maggots are yellowish-white, only 0.2 inches long, and some species have pointed ends. Pupae are oblong with a forked breathing tube at one end. Some insects, such as Malaysian fruit flies (Bactrocera latifrons) are actually blowflies, and not true fruit flies. There are two major families of fruit fly: Drosophila and Tephritidae. 

​Drosophila flies

Because of their short lifecycle and profound reproduction rates, Drosophila, also known as vinegar flies or common fruit flies, are very popular in genetic research laboratories. The common fruit fly genome is well documented, with only four pairs of chromosomes. Two common species are D. melanogaster and D. simulans. Only one of the common fruit fly’s claims to fame includes the fact that their sperm cells are 2.4 inches long, which is 20 time longer than the fly, and 1,000 times longer than human sperm cells. I don’t know how they do it.

Tephritidae fruit fly (Bruce Marlin) CC BY-SA 2.5

Tephritidae flies
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Tephritidae flies are sometimes referred to as peacock flies, due to their colorful markings. These markings often mimic other, actually dangerous insects. This copy-cat behavior is called Batesian mimicry, in case you were curious. There are over 5,000 species within this family, including apple maggots, western cherry fruit flies, walnut husk flies, and the dreaded Mediterranean fruit fly (Ceratitis capitata), or medfly. Unlike common fruit flies, members of this group lay eggs in leaves, stems, flowers, seeds, and roots, as well as in fruit. One member of this family, Euphranta toxoneura, deposits eggs in galls created by sawflies.

​Fruit fly damage

As fruit fly larva feed on ripe fruit, they leave a trail of frass (bug poop). They also create points of entry for yeasts that cause souring, along with other pests and diseases. Fruit flies on grapes (Drosophila spp.) can lead the way to bunch rot spreading throughout your vines. The olive fruit fly (T. Bactrocera oleae), considered the world’s worst olive pest, has been known to destroy entire crops. 

​One species of fruit fly, D. suzuki, also called spotted wing drosophila, has a taste for soft fruits, such as raspberry, strawberry, blackberry, cherry, and blueberry. There is not enough information available at this time to determine what sort of an impact these pests will have on those crops, but it doesn’t look good.

Fruit fly controls

Outside of your kitchen, fruit flies are prey to robber flies, yellowjackets, ants, and certain beetles. Since ripe fruit is what attracts fruit flies in the first place, regularly harvesting fruit crops, such as tomatoes, melons, squash, grapes, and olives before they become overripe, can reduce fruit fly populations. Be sure to throw out the mummies, while you’re at it. Overripe potatoes and onions can also attract fruit flies. So can sink drains, mops, garbage disposals, trash cans, cleaning rags, recycling bins, and empty bottles. All fruit flies need is warmth, moisture, and something fermentable to eat. Eliminating any one of those three conditions can break the fruit fly triangle. Insecticides are not effective as long term controls, but pheromone traps can be used to interrupt fruit fly mating.

You can make your own fruit fly trap with a glass and a funnel. Simply place a piece of overripe fruit, some yeast and water, or cider vinegar, beer, or wine in the bottom of the jar and place the funnel on top, similar to a green fruit beetle trap. [Do not use apple cider flavored distilled vinegar - we may be fooled but fruit flies are not.] Fruit flies will be attracted to the bait and find their way in, but will be unable, for the most part, to find their way out. [If your funnel has spacers on the outside edges for air flow, cover the space with tape.] Every few days, take your trap apart and wash it with soap and water, before adding new bait. Within a couple of weeks, your fruit fly problem should be gone. Just be sure that you do not throw the contents of your trap in the trash, as it will contain hundreds of fruit fly eggs just waiting to hatch! Use soap and hot water to wash the glass and funnel. Let the hot, soapy water flow into the drain for at least one minute to wash any fruit fly breeding grounds out of your pipes.

As for those bananas you bought at the grocery store - rinse them off as soon as you get home. This will help to dislodge any fruit fly eggs before they can hatch. And refrigerating produce will halt the development of any fruit flies that remain.