Melon fly

Adults

• About the same length (approximately 7mm) as a common housefly but more slender like a small wasp.
• Yellowish in colour.
• 3 yellowish-white stripes on the 'back' between the wings; one either side and one down the middle.
• 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 to yellowish-white, long elliptical – like a sickle, and approximately 1–2mm long.

Larvae

• Maggots are creamy-white and up to 10mm long at full size (younger stages are smaller).

Pupae

• Varies in colour from white to yellow-brown.
• Roughly cylindrical.
• Approximately 5mm long.
• Typically found in the soil.

Plant stage and plant parts affected

• Flowers and fruit.

Plant damage

As with other fruit fly species, females 'sting' the plant when they lay their eggs. 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
• fruit rot and premature fruit fall.

Compared to melon fly, the Queensland fruit fly is a similar size but is an overall reddish-brown colour without the patterns on the wing or triple stripes 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.

Widespread in Asia, sub-Saharan Africa and in the Pacific (Hawaii, Guam, Kiribati, Nauru, Northern Mariana Islands, and the Solomon Islands).

It is closest to Australia in Indonesia, Timor Leste and Papua New Guinea.

Melon fly has been recorded on 44 host species from 12 plant families.

It is mainly a pest of cucurbits such as melon, pumpkin, squash, zucchini, and cucumber; host species also include beans, tomato, papaw, and guava in South-East Asia.

• Melon flies are active throughout the year.
• Eggs are laid in flowers, fruit and vegetables.
• Within 1–2 days, eggs hatch into larvae (maggots) that feed within the fruit and vegetables, and can cause premature fruit fall.
• Depending on a range of factors, including temperature, after 6–35 days the larvae drop from the fruit to ground level, bury in the soil, and pupate.
• Flies emerge after another 10–12 days (depending on conditions).
• Flies live for several months; females are capable of laying eggs throughout their life span once mated.

In 2020–2021, the gross value of production of Queensland horticulture crops (excluding cut flowers, nursery and turf) was $2.9 billion (Queensland AgTrends).

Cucurbit crops such as cucumber, melon and pumpkin, and other vegetables such as beans and tomatoes are grown for both domestic consumption as well as international export markets.

Melon fly would have serious consequences for our horticultural industries if it established in Queensland. 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 would also be affected with loss of produce to fruit fly infestation.

Melon fly could easily be brought into Australia by illegal importation of infested fruit.

Melon fly occasionally moves into the Torres Strait with monsoonal winds in the wet season and is eradicated as part of a highly successful, proactive eradication strategy.

Like most tropical fruit fly species, melon fly multiplies rapidly and can spread over large distances.

Check your fruit and vegetables, particularly cucumber, melon, pumpkin, squash and zucchini. If you have fruit and vegetables 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.

If you have Queensland fruit fly traps, look at the dead flies to see if any have dark patches on their wings. Adult fruit flies may also be found near your infested fruit resting on plants. Examine them. If you find that the infesting fruit flies have dark patches on their wings, report them. If you find fruit flies infesting flowers of cucurbit plants in particular, then it is possible that you have an exotic fruit fly species on your property.

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

• Protect your farm from emergency plant pests
• Understand good farm biosecurity
• Visit the farm biosecurity website

The nationally cost-shared Exotic Fruit Flies in Torres Strait Eradication Program undertakes surveillance 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. Any incursions are immediately eradicated as part of this program.

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.

Melon fly is prohibited matter 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 in Schedule 8 of the Biosecurity Regulation 2016. 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 or email qld.plantquarantine@daf.qld.gov.au.

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