Melon fly

  • Photo of adult melon fly
    Photo of adult melon fly
  • Photo of adult Queensland fruit fly
    Photo of adult Queensland fruit fly

Have you seen melon fly?

In Queensland, melon fly (Bactrocera cucurbitae) is listed as prohibited matter under the Biosecurity Act 2014.

Be on the lookout for melon fly and report it to Biosecurity Queensland.

Early detection and reporting are the key elements in controlling melon fly.

Call Biosecurity Queensland 13 25 23

General information

Melon fly (Bactrocera cucurbitae) is a serious pest of horticultural crops.

It is important to let us know as soon as you suspect melon fly so that it can be eradicated before it becomes too widespread. 

Overview

Females 'sting' the fruit when they lay their eggs inside. Larvae tunnel into the fruit and considerable damage can occur inside the flesh before obvious signs can be seen on the fruit. The most obvious signs of infestation are:

small, discoloured patches on the skin, which develop from the stings

affected fruit will rot and often fall from the plant prematurely

larvae feeding on cucurbit flowers and stemsgreen fruit may be affected.

Species name

Bactrocera cucurbitae (Coquillett)

Description

Appearance

  • About the same length as a common housefly but more slender.
  • Similar to a small wasp.
  • Grows to 7 mm in length. 
  • Yellowish colour. 
  • Yellow/white stripe in the middle of the thorax between the wings.
  • A black (often incomplete) T-shaped marking on the abdomen (the rear body section).
  • Additional dark patches towards the outer edge of the wings (see photo 1).

Similar species

The Queensland fruit fly (Bactrocera tryoni) is a similar size but is an overall reddish-brown colour, without the patterns on the wing or middle yellow stripe on the chest. An expert eye is needed to identify melon fly under a microscope (see photo 2). Traps used to catch Queensland fruit fly can also catch exotic fruit flies, so it is important to check traps for melon fly.

Cucumber fly (Bactrocera cucumis) is a native species which infests similar hosts to melon fly. Like melon fly, it is yellow with a yellow to white stripe in the middle of the thorax; however, its wings do not have the additional dark patches. Cucumber flies are not attracted to the traps used to catch Queensland fruit fly.

Distribution

Melon fly is widespread throughout the world including southeast Asia, India, China, Japan and Nepal. It is also established in the Middle East (Saudi Arabia and UAE), Africa and several Pacific islands (Hawaii, Guam Kiribati, Nauru, Northern Mariana Islands Solomon island).

It is well established in Papua New Guinea and has been detected several times in the islands of Torres Strait. It has not established a presence as any detection is immediately eradicated under the Torres Strait Exotic Fruit Fly Containment Program.

Life cycle

Melon flies are active throughout the year. The adult female fly lays eggs in fruit leaving punctures or stings in the skin, and the eggs hatch into larvae (maggots). When larvae have finished feeding on the fruit, they burrow into the soil, pupate then emerge as adult fruit flies. This life cycle will typically take 3-5 weeks for completion in summer, and longer over winter.

Hosts

Melon fly prefers beans and cucurbits such as melon, pumpkin, squash, zucchini and cucumber. In southeast Asia, host species have included beans, tomato, papaw and guava. Native fruit flies will also attack cucurbits, particularly the softer types, but the damage is generally less severe.

Symptoms

Females 'sting' the fruit when they lay their eggs inside. Larvae tunnel into the fruit and considerable damage can occur inside the flesh before obvious signs can be seen on the fruit. The most obvious signs of infestation are:

  • small, discoloured patches on the skin, which develop from the stings
  • affected fruit will rot and often fall from the plant prematurely
  • larvae feeding on cucurbit flowers and stems
  • green fruit may be affected.
Impacts Melon fly could easily be brought into Australia by illegal imports of fruit. If it occurs, costly quarantine restrictions and eradication measures will be required.

If melon fly established in Queensland, it would have serious consequences for our horticultural industries. Many countries have trade restrictions on fruit that come from regions known to have melon fly. Growers would likely face difficulties exporting their produce.
Spread Like most tropical fruit fly species, melon fly multiplies rapidly and can spread over large distances. It is capable of establishing in most of Australia.
Risk period Melon fly occasionally moves into the Torres Strait with the monsoonal winds each wet season and is eradicated annually as part of a proactive containment strategy by the Queensland and Australian Governments.The greatest risk period for incursion from this pathway is over summer, although it could also be introduced through illegal imports of fruit. 
Monitoring and action

If you have fruit and vegetables, particularly beans or cucurbits that have had no problems with fruit fly in the past but are now infested with maggots, then it is possible that you have an exotic fruit fly species on your property.

Keep a look out and let us know if you notice unusual fruit flies or there are changes in the pattern of damage to crops.

Government monitoring

Queensland Government monitors a network of traps for melon fly in high-risk urban and remote centres in Queensland. Australian Government conducts surveillance for melon fly on each inhabited island in Torres Strait. If it is detected in Queensland, we have well-planned eradication strategies in place.

Control

Treatment

More intensive or regular treatments may be required in some crops, because of the high levels of damage melon fly can inflict.

Quarantine restrictions

Should an incursion of this pest occur, the Australian and Queensland Government would likely:

  • impose quarantine restrictions on affected areas
  • increase trapping to determine the extent of the affected area
  • implement eradication methods to kill any melon flies detected.

Further reading

  • M.K. Dhillon, Ram Singh, J.S. Naresh, and H.C. Sharma. (2005). The melon fruit fly, Bactrocera cucurbitae: A review of its biology and management. Journal of Insect Science: 5: 40.

Last updated 19 February 2015