Queensland fruit fly

Scientific name

Bactrocera tryoni

Description of adult

The adult is wasp-like, red-brown with yellow marks, and about 8mm long. Unlike cucumber fruit fly there is no central yellow mark down the length of the dorsal surface of the thorax between the wings. Fruit flies hold their wings outstretched in a horizontal position when walking. They flick them in a characteristic manner.

Immature stages

The female pierces (stings) the maturing fruit and lays a clutch of white, banana-shaped eggs just below the surface. Hatching takes place after 2 to 3 days and the resulting larvae are white carrot-shaped maggots (about 7mm long when mature) that tunnel in the flesh. They carry bacteria that aid in fruit breakdown. The mature larvae can 'jump' by curling into a 'U'-shape and then rapidly straightening.

Life history

Larvae mature in 7–10 days in summer and emerge from the fruit to pupate in the soil. The pupal stage lasts about 10 days. The life cycle takes about 2.5 weeks during summer. The adult flies congregate on foliage and fruit to feed on bacterial colonies and later to mate. These bacterial colonies are more plentiful under humid conditions.

Distribution

Queensland fruit fly is a native pest occurring throughout eastern Australia.

Host range

Queensland fruit fly infests both indigenous and introduced fruits. Commercial varieties affected include abiu, apple, avocado, babaco, capsicum, carambola, casimiroa, cherry, citrus, custard apple, granadilla, grape, guava, kiwifruit, mango, nectarine, papaya, passionfruit, peach, pear, persimmon, plum, pomegranate, prune, quince, loquat, santol, sapodilla, tamarillo, tomato and wax jambu.

Damage

Major and frequent pest. Activity is greatest in warm humid conditions and is particularly important where tree-ripened fruit are concerned.

Adults lay eggs ('sting') in the fruit and the larvae feed in the flesh. Affected fruit are readily recognised since rots develop rapidly and the skin around the sting marks becomes discoloured. Queensland fruit fly damage is more severe during mid and late summer than at other times. Large numbers of flies can be expected after good falls of summer rain; fruit flies become active after periods of rain or high humidity.

To monitor fruit fly activity hang male lure traps under the shady canopy, where flies tend to rest. Check the number of flies trapped each week. The recommended trap contains a synthetic attractant combined with a fumigant insecticide. Growers need to seriously consider whether fruit flies are causing sufficient damage to warrant spraying. A number of traps (1 per hectare) should be hung in the middle of each large orchard block of 5.0ha or more according to manufacturer's instructions. Inspect traps at weekly intervals from the end of flowering and until the completion of harvesting. Control maybe necessary as soon as 2 flies per trap per day are caught.

Control

Cultural

Fruit flies become active after periods of rain or high humidity. Sprays for fruit fly control may not be necessary in dry seasons. Do not allow fallen fruit to accumulate under trees.

Biological

While there are a number of parasitoids that can help control fruit fly populations, these kill the insect in the pupal stage and are therefore of little use in preventing damage if populations are already high. However, they do help to reduce the next generation of flies, particularly in isolated or marginal fly areas.

Chemical

Apply cover sprays as needed if approved on the affected crop. A protein bait for the control of female fruit flies is approved for use on various tree, fruit, vine and vegetable crops, and can be applied in spots or bands on foliage. Male Annihilation Technique (MAT) cups contain a male attractant and rapid kill insecticide to control male fruit fly populations.

Chemical registrations and permits

Products containing Fenthion (Lebaycid) for pre-harvest and post-harvest control of fruit flies must not be used as they are no longer registered and may pose undue risks to human health and the environment. Dispose of unused chemical products according to the legislative requirements of the Department of Environment, Science and Innovation.

Registered and permitted products are available to control fruit flies, which include cover sprays, fruit dips and bait sprays. The use of multiple techniques (trapping, baiting, chemical and cultural) can be effective in controlling fruit flies.

Check the Australian Pesticides and Veterinary Medicines Authority database for chemicals registered or approved under permit to treat this pest on the target crop in your location. Always read the label and observe withholding periods.