Diptera: Tephritidae

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Image above: Mediterranean Fruit Fly

Fruit Flies are Australia’s most serious fruit pests. The most widespread species of Fruit Fly is the Queensland Fruit Fly (Bactrocera tryoni), a native insect, which is found in all states of mainland Australia except Western Australia.

Western Australian gardeners must contend with the introduced Mediterranean Fruit Fly (Ceratitis capitata), also known as ‘medfly’, which has not established in eastern Australia, but does occur seasonally in South Australia.

Both species attack a wide variety of fruits, including citrus, stone, pome, tropical fruits and some fruiting vegetables. Restrictions apply to the movement of fruit between various states and territories, to control the spread of both these species of Fruit Fly. Check guidelines supplied by the states before crossing borders if carrying fresh fruit.

Best Treatment for Fruit Fly

The secret to pest control is to keep an eye on your fruiting plants, so that you can spot pest incursions early. This is especially critical with Fruit Flies. If you miss the first Fruit Fly incursion of the season, you might have an even bigger problem later in the season.

Monitoring your trees with traps is an excellent option. Fruit Flies are quite small and not easily spotted, but the traps will do that for you (see Monitor). Some traps may catch other insects as well as Fruit Flies, so you need to know what Fruit Flies look like (see Description).

Prevention is always better than cure. There are several measures that you can do to prevent or minimise damage by Fruit Flies (see How to Prevent Fruit Flies Appearing). Apart from exclusion bags and nets, there is no easy way to prevent fruit fly infestations.

Fruit Fly control is mandatory in some states, for example some regions of Western Australia. Contact your local Department of Primary Industries or your Municipal Council for information if you are in a Fruit Fly area.

To control Fruit Fly, try Yates Nature's Way Fruit Fly Control, which attracts males and females of both Queensland Fruit Fly and Mediterranean Fruit Fly with a protein and sugar-based bait. The flies feed on the bait that also contains Spinosad, an insecticide derived from a naturally occurring bacteria, that kills them. Follow label instructions. Baits such as this are based on knowledge about Fruit Flies. The flies need sugar for energy and protein for reproduction, which makes the bait doubly attractive to them.

The Fruit Fly control methods mentioned here aren’t mutually exclusive, you may need a combination. For example, you can use fruit fly traps to alert you to the presence of flies. You could then apply Yates Nature's Way Fruit Fly Control. You could also manage fallen fruit to prevent more flies emerging.

If your prevention methods fail, and an infestation occurs, destroy all infested fruit to prevent a new generation emerging in your backyard. Encourage your neighbours to be as diligent as you. Fruit Fly control is more effective with a neighbourhood approach, because these insects can fly.

What are Fruit Flies &
How to Get Rid of Them

Fruit Flies are flies whose larvae feed in the fruits of various fruit trees, as well as in the fruits from several fruiting vegetables. They should not be confused with the fly that breeds in compost bins (Drosophila melanogaster) and is known in Australia as the ‘Vinegar Fly’, but in the US as ‘Common Fruit Fly’. Vinegar Fly is from a different family – Drosophilidae – and not from the family of true Fruit Flies – Tephritidae.

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Image above: Queensland Fruit Fly (Bactrocera tryoni)

Description

Adult

Queensland Fruit Fly (Bactrocera tryoni) is about 7 mm long, and reddish-brown with yellow markings.

Mediterranean Fruit Fly (Ceratitis capitata) is about 3-5 mm long, with a yellow abdomen, black patterned thorax, and banded wings.

A significant difference between the two flies is that Mediterranean Fruit Fly do not move very far – about 50 m – while Queensland Fruit Fly may travel 10 times that distance.

Egg

Eggs are translucent white, about 1 mm long and slightly curved like a banana.

Larva

Larvae are creamy-white maggots with pointed heads that grow to about 7 - 9 mm long.

Pupa

Pupae are brown cylindrical capsules about 4 mm long.

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Image above: Fruit fly larvae
(image courtesy of Elise Dando)

Life Cycle

Queensland Fruit Fly females lay 500 − 800 eggs in fruit over about four months. Mediterranean Fruit Fly females lay about 300 − 800 eggs during a 2 to 3-month life span. Queensland Fruit Fly lay about 12 eggs into each ‘sting’ hole, while Mediterranean Fruit Fly may lay up to 30 at a time. Several females may lay eggs in the same fruit at the same time, resulting in many larvae within one fruit.

Female flies punch a hole in the skin and lay eggs in (‘sting’) fruit that is just beginning to ripen. Fruit Fly larvae hatch from the eggs and burrow inside the fruit to feed on the pulp. When the larvae are mature, they chew a hole in the fruit skin and drop or ‘jump’ to the ground where they pupate in the soil. Adult flies cut through the pupal case and burrow up through the soil to begin a new generation.

The life cycle can be completed in about four weeks in warm, moist conditions and there may be as many as six generations per year. In cooler weather, life cycles may take up to 4 months to complete.  Fruit Fly activity peaks in late summer but can occur from spring to autumn in warmer regions.

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Image above: Guava fruit infested with Fruit Fly larvae
(Image courtesy of Elise Dando)

What Plants are Impacted by Fruit Flies

  • Citrus, including cumquats, lemons, limes and oranges
  • Pome fruit - apples, nashi, pears and quinces
  • Stone fruit – apricots, nectarines, peaches and plums
  • Avocadoes, banana, figs, guava, loquats, mangoes, passionfruit, persimmons, pomegranates and strawberries
  • Fruiting vegetables such as capsicum, eggplant and tomatoes
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Image above: Pinkprick holes ('stings') in the skin of an orange
(image courtesy of Elise Dando)

Symptoms of Fruit Fly Damage

  • Pinprick holes (‘stings’) in fruit.
  • Larvae in fruit.
  • Dropped fruit
  • Rotting fruit – caused by secondary infections following Fruit Fly larvae feeding.
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Image above: orange infested with Fruit Fly larvae
(image courtesy of Elise Dando)

How to Prevent Fruit Flies Appearing

Monitor

  • Watch for small flies around your fruit trees.
  • Use commercially available Fruit Fly lure traps to catch flies. Some traps only catch males, which alert you to the first active flies of the season, helping with timing of control methods. A trap which catches males and females is best. Even then you will need to employ other treatments to fully control this pest.
  • Make your own lure trap. Make up a bait fluid in a jar and suspend it in one of your trees. There are several bait recipes online such as a mixture of 80 g white sugar, 1.5 g dry brewer’s yeast and 920 mL water.

Prevent

  • Use paper or fine mesh cloth exclusion bags to prevent maturing fruit being stung.
  • Use exclusion netting on the whole tree. The net must have a weave of about 2 mm x 1 mm to prevent entry by Fruit Flies. Make sure the net is not touching any fruit or Fruit Flies may lay eggs through the net.
  • Pick up any fallen and infested fruit and dispose of in a plastic bag, helping to reduce fly numbers.
  • Pick ripe fruit immediately to reduce breeding sites.
  • Prune fruit trees to make harvesting fruit manageable.

Natural enemies

  • Assassin bugs, mantids and spiders eat adult flies.
  • Parasitic wasps sting fruit fly larvae in fruit (see beneficial wasps).

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