Melon fly

Alert

Have you seen Melon fly?

Be on the lookout and report it.

Under Queensland legislation if you suspect the presence of Melon fly, you must report it to Biosecurity Queensland on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.

Early detection and reporting are key elements in controlling Melon fly.

Melon fly (Zeugodacus cucurbitae) is a serious pest of vegetable crops, especially cucurbits such as melon, pumpkin, squash, zucchini and cucumber.

Contact us immediately if you suspect melon fly so that it can be eradicated before it becomes too widespread.

Melon fly can be seasonally dispersed during the monsoon season into the Torres Strait region where is it promptly eradicated. Melon fly has been declared a far northern pest. The far northern biosecurity zones 1 and 2 (PDF, 333KB), and their associated movement restrictions, are in place to prevent this pest and other far northern pests from spreading.

Other names

  • Bactrocera cucurbitae (Coquillett)

Description

Adults

  • About the same length as a common housefly but more slender like a small wasp.
  • Approximately 7mm in length.
  • Yellowish colour.
  • 3 yellow to white stripes in the middle of the thorax between the wings.
  • A black, often incomplete T-shaped marking on the abdomen (the rear body section).
  • 2 dark brown patches towards the outer edge of the wings (see images above).

Eggs

  • White, elliptical and about 2mm long.

Larvae

  • Maggots are typically white, similar to other fruit flies.
  • About 7.5–9.5mm long.

Pupae

  • Varies in colour from dull red to brownish-yellow to dull white.
  • About 5–6mm long.
  • The larvae change into adult flies within the pupa.

Plant stage and plant parts affected

  • Flowers and fruit, or sometimes succulent plant stems and roots of host plants.

Plant damage

As with other fruit fly species, females 'sting' the plant when they lay their eggs inside. Larvae hatch from eggs and tunnel into the fruit or other plant parts and considerable damage can occur inside the flesh before obvious signs can be seen on the outside.

Fruit decaying bacteria are deposited within the fruit during the egg laying process. These bacteria also contribute to fruit damage.

The most obvious signs of infestation are:

  • small discoloured or water-soaked patches on the fruit skin, which develop from the stings
  • affected fruit rotting and often falling from the plant prematurely.

May be confused with

The Queensland fruit fly is a similar size but is an overall reddish-brown colour without the patterns on the wing or middle yellow stripe on the back of the thorax. Traps used to catch Queensland fruit fly can also catch exotic fruit flies, so it is important to check traps for melon fly.

Melon flies have dark patches on the wings (see images above). Native fruit flies that affect similar host plants such as Queensland fruit fly or cucumber fruit fly do not have dark patches on the wings.

An expert is needed to identify melon fly under a microscope so please report any suspect exotic fruit fly species.

Hosts

Melon fly is mainly a pest of cucurbits such as melon, pumpkin, squash, zucchini and cucumber.

In South-East Asia, host species also include beans, tomato, papaw and guava.

Life cycle

  • Melon flies are active throughout the year.
  • Eggs are laid in flowers and fruit, or succulent plant stems or roots
  • In fruit, the punctures or stings in the skin can also deposit fruit decaying bacteria in the wound.
  • Eggs hatch into larvae (maggots).
  • When larvae have finished feeding, they drop from the fruit to ground level and burrow into the soil to pupate.
  • Adult fruit flies emerge from the pupa.
  • After mating, adult female flies are capable of reproducing throughout much of their life span. They can lay about 1,000 eggs.
  • The time from egg to adult emergence varies, and is generally about 2–3 weeks, and longer over winter.
  • The lifespan of an adult fly varies depending on many factors, and can be as long as 5–15 months.

Impacts

Cucurbit crops such as cucumber, melon, pumpkin, squash and zucchini are significant crops in Queensland. They are grown for both domestic consumption as well as international export markets.

In 2016–17 the farm gate value of Australia's cucurbit crop was over $500 million, comprising cucumbers $182 million, melons $172 million,  pumpkins $76 million and zucchinis $70 million. Queensland grows over a third of Australia's cucumbers, melons and pumpkins and nearly half of Australia's zucchini crop (source: Australian Horticulture Statistics Handbook, 2016-2017 Hort Innovation).

If melon fly established in Queensland, it would have serious consequences for our horticultural industries. Many countries have trade restrictions on produce that comes from regions known to have melon fly. Growers would likely face difficulties exporting their produce due to the quarantine restrictions imposed by importing states and countries.

Home growers of cucurbits such as cucumber, melons, pumpkin, squash and zucchini would also be affected with loss of fruit to fruit fly infestation.

Control

The nationally cost-shared Exotic Fruit Flies in Torres Strait Eradication Program undertakes surveillance for eradication of melon flies and other exotic fruit fly species that may be seasonally dispersed from Papua New Guinea to the Torres Strait Islands with the summer monsoon season.

The program includes:

  • trapping and identifying fruit flies for early detection
  • using pheromone-based insecticide baits (blocks) to attract and kill male fruit flies
  • using protein-based insecticide bait (spray) to kill adult female flies
  • movement restrictions to prevent pest introduction and spread by movement of infested fruit and vegetables.

Legal requirements

Melon fly is a prohibited plant pest under the Biosecurity Act 2014.

Report suspected melon fly to Biosecurity Queensland immediately on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.

If you think you have found melon fly, you must take all reasonable and practical steps under your control to minimise any associated risks. This is called a general biosecurity obligation (GBO).

Melon fly is also a declared far northern pest. The far northern biosecurity zones (PDF, 333KB) have been established to prevent the spread of far northern pests.

Regulations are in place to restrict the movement of fruit and vegetables, plants and other plant material, soil and equipment (collectively called far northern pest carriers) which may harbour pests and diseases. You must apply for a biosecurity instrument permit to move any of these items out of the far northern biosecurity zones.

It is illegal to move a far northern pest such as melon fly, or far northern pest carriers without a biosecurity instrument permit:

  • from far northern biosecurity zone 1 to a place outside of that zone
  • from far northern biosecurity zone 2 to a place outside that zone, unless it is into far northern biosecurity zone 1.

You must observe movement restrictions if you are travelling to or around the Cape York Peninsula, or if you live there.

For more information about biosecurity instrument permits, contact the Customer Service Centre on 13 25 23 (from interstate use (07) 3404 6999) or email qld.plantquarantine@daf.qld.gov.au.

Biosecurity Queensland inspectors at the Cape York Biosecurity Centre at Coen check vehicles moving south from Cape York Peninsula to ensure that pests or pest carriers are not moved from the zone.

Your cooperation in complying with these restrictions will help protect Queensland from exotic fruit fly outbreaks.

Further information