Control of Mediterranean Fruit Fly (Medfly) in Backyards


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The Mediterranean fruit fly - Ceratitis capitata

The Mediterranean fruit fly (Medfly) is thought to originate from tropical Africa. It is a pest in many areas of the world including Western Australia. It was first detected at Claremont in 1895 and is now found as far south as Esperance and as far north as Derby. The main area of infestation extends from Carnarvon to Bunbury.

Medfly is known to infest over 200 fruit and vegetable species. In Western Australia, stone fruit, pome fruit, citrus, loquats and guavas are particularly susceptible.
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Life cycle
The onset of Medfly activity is temperature dependent. In the south-west of the State Medfly is active in late spring, summer and autumn. In winter, the fly may become inactive in cold areas. Medfly can overwinter as adults, as eggs and larvae (in fruit), or as pupae in the ground. Adult Medfly are active in winter when temperatures exceed 12 ║C (see Fig. 1).

As temperatures increase in spring, adults begin to emerge from the ground and overwintering flies become active. If control is not started at this time, Medfly populations will increase to cause problems later in the season.

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Fig. 1. Life cycle of the Mediterranean fruit fly

Adult
The adult fly is 3-5 mm long, slightly smaller than a housefly. The body is light brown. The wings are mottled with distinct brown bands extending to the wing tips. The abdomen is brown, encircled by two light coloured rings. The thorax (middle) has irregular patches of black and silver, giving it a mosaic appearance. The female Medfly has an ovipositor; the male does not. Adult Medfly may live for 2-3 months and are often found in foliage of fruit trees. As long as fruit is present, most Medfly do not move very far - 20-50 m.

Eggs
After mating, females search for a suitable host. Fruit such as apricots are preferred to hosts such as apples and pears. However, when Medfly populations are high, females become less choosy and will infest less preferred hosts such as olives. Female Medfly will also infest less preferred hosts if preferred hosts are not available, even when populations are low.

Larvae (maggots)
The eggs hatch within 2-4 days into larvae. The larvae are white with a flat, pointed head. It is this stage of the life cycle that you are most likely to see. When the larvae first hatch they are about l mm long, but quickly grow to 8 mm. The larvae feed on the flesh of the fruit, causing it to decompose. When fully grown, larvae stop feeding and leave the fruit, burrowing into the soil to pupate.

Pupae
Pupae resemble a small brown capsule or barrel about 4 mm long. Within the pupae the Medfly slowly develops into an adult. The adult fly cuts through the pupal case and burrows up through the soil.
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Control

It has been estimated that if control methods were not used, Medfly would infest 100 percent of susceptible fruit such as apricots, nectarines, peaches and mandarins and to a lesser extent, fruits such as apples and pears. All citrus is susceptible in warm winters. Only early maturing varieties of stone fruit or fruit fly tolerant varieties of fruit such as some lemon cultivars and avocados can be grown without insecticide applications.

Two control methods are currently recommended: foliage baiting and cover spraying. Foliage baits are used to control the adult population; cover sprays control adult Medfly and provide some control of eggs and larvae.
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Hygiene

For chemical methods to be effective, fly-infested or unwanted fruit must be destroyed. Fruit can be destroyed by soaking it in water, topped with a layer of kerosene for 4 -5 days. Medfly larvae can survive in water for a few days unless their oxygen supply is cut off. The kerosene layer prevents oxygen exchange between the air and water.

Freezing fruit for a few days, or cooking or pureeing fruit (which can then be fed to poultry or pigs) are other methods of disposal. Burial is not recommended since Medfly larvae can survive burial. Do not take fly-infested fruit to the dump without first treating it.
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Foliage baiting

Foliage baits consist of an insecticide (maldison) and a source of protein. The female Medfly requires a source of protein for the maturation of her eggs and in the 'wild', can obtain this from substances such as fruit juices, bacteria and bird droppings. By providing a protein and insecticide in one formulation, the bait is attractive as a food source to both male and female Medfly. The baits are eaten by the adult Medfly, which forage over the leaves for food.

Application
You do not need to spray the entire tree with the bait since Medfly will be attracted from a few metres away. Aim the bait into the middle (Fig. 2) rather than the extreme top or bottom of the tree, and into the centre rather than the outer foliage. Avoid hitting the fruit with the bait mixture and avoid baiting trees with ripe fruit.

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Fig. 2. How to apply foliage bait

Apply bait in the morning if possible. If you apply bait at midday or in the evening, there is a risk of burning or scarring leaves and fruit.

In urban and peri-urban areas, all fruit trees should be baited. If the Medfly population is particularly high, the number of trees baited can be increased to include non-fruiting trees and non-fruit trees (i.e. decoy trees), or the frequency of baiting can be increased to once a week. In cooler months or on isolated properties, the frequency of baiting may be decreased to once every fortnight. Rain will wash off foliage baits, so after heavy rainfall you should reapply the bait.

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Table 1. Insecticides recommended for foliage baiting

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Table 2. Proteins to be added to insecticides listed in Table 1


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Cover spraying

Cover spraying differs from bait spraying in that all stages of the lifecycle (egg to adult) are killed. However, in addition to Medfly, any other insects present at the time of spraying will be killed.

Cover sprays kill Medfly adults on contact and destroy eggs and larvae through penetrative action. Cover sprays will not stop the female Medfly from stinging fruit. If the Medfly population in the surrounding area is particularly high, foliage baits provide additional control.

Three insecticides are currently registered for use in Western Australia (Table 3).

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Table 3. Insecticides recommended for cover spraying

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Application

Start spraying when the fruit is one half to two-thirds of its full size, or if sustained numbers of Medfly are caught in traps. The aim is to cover the fruit with insecticide (5-10 L/tree; Fig. 3). The amount of insecticide used depends on the size of the tree: larger trees require more insecticide, smaller trees require less. The withholding period is 2-7 days depending on which insecticide is used (Table 3).

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Fig. 3. How to apply cover sprays
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Trapping

Trapping is not recommended as a control method because it does not control the adult population. However, it is a useful tool for detecting Medfly populations and will help reduce the number of Medfly in your backyard.

Trap types
Three types of traps are used to catch Medfly: male lure, female lure or wet traps. The male lure trap consists of a pheromone and an insecticide (Fig. 4). A pheromone is a chemical that attracts a male or female of a species. Male Medfly are attracted to the pheromones trimedlure and capilure. The male Medfly is lured into the trap where it is killed by insecticide. Female traps consist of a McPhail trap (Fig. 5) and a lure such as "Biolure".

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Figure 4. Lynfield trap - used for monitoring
populations of male Medfly

Figure 5. McPhail trap - used for monitoring
populations of female Medfly

Wet or food traps consist of a food source such as protein or sugar, and should contain insecticide. The flies are attracted to the food source, enter the trap and are then killed by the insecticide. In insecticide-free traps, flies enter the trap but are unable to leave, eventually drowning in the lure at the bottom of the trap. Wet traps are attractive to both sexes but other insects such as bush flies, ferment flies, wasps, crickets and beetles may also be caught.

Traps are commercially available in Western Australia from nursery and garden suppliers (Fig. 5). A home-made trap can be made from a plastic 1 or 2-litre cool drink container by punching small holes (8 mm diameter) into the middle of the bottle (Fig. 6). Another alternative is to modify a 2-litre plastic milk bottle, by cutting four flaps in each of the sides (Fig. 6).

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Fig. 6. Making a fruit fly trap

Make up fresh trap solutions each time that they are required. Traps should be rinsed or replaced every few weeks. Replace the solution fortnightly, weekly if blowflies are being attracted to the trap. You will need more lure during warmer weather as the solution will evaporate. For best results, place at least two traps per fruiting tree (max. 6 traps per tree). For every three traps used in fruit trees, place one trap in a non-fruiting tree or shrub as a decoy. This will help reduce the number of Medfly going to your fruiting trees. If the number of flies caught in the traps show a sustained increase, then start baiting or cover spraying.

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Table 4. Wet trap solutions


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Other insects that could be confused with Medfly

Ferment/vinegar fly
Medfly may be confused with Drosophila melanogaster, the ferment or vinegar fly (Figs. 7). Ferment flies are often used in school experiments and are sometimes referred to as a fruit fly. Ferment fly however, are not true fruit flies. They are usually found around rotting fruit (Medfly is not). Ferment flies are also much smaller, l mm compared to 4 mm for Medfly (Fig. 8).

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Fig. 7. Adult Drosophila melanogaster
Image ęPaul Zbrowski

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Fig. 8. Difference in size between ferment fly (left) and Medfly (right)

Metallic-green tomato fly
The metallic-green tomato fly (Lamprolonchaea brouniana) is about 6 mm long. The adult has a metallic sheen, whereas the Medfly does not have a sheen. The larvae of the metallic-green tomato fly can only be distinguished from Medfly under a microscope.

Queensland fruit fly
The Queensland fruit fly (Qfly), Bactrocera tryoni, was accidentally introduced into Western Australia from the Eastern States. The Qfly was eradicated from the Perth metropolitan area in 1990. Qfly traps have been installed throughout the state to monitor for any further incursions. A separate farmnote is available on identification of Queensland fruit fly and other exotic fruit flies (Farmnote No. 63/99).


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Plant Diseases Act

The Plant Diseases Act has regulations that govern the control of fruit fly. For further information about regulations, contact Agriculture Western Australia on telephone (08) 9368 3333.

Note: Mention of trade names does not imply endorsement or preference of any company's product by Agriculture Western Australia and any omission of a trade name is unintentional. Recommendations are current at the time of printing.

Require more information? Contact the AGWEST Garden Advisory Centre on

9368 3666


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Authors: Sonya Broughton and Francis De Lima.