IPDM in focus: Queensland fruit fly

Prepared by Ruby Rhodes and Greg Lefoe, Agriculture Victoria, using information from the Integrated Pest, Disease and Weed Management Manual for Australian Apples and Pears (IPDM Manual, Edition 2, 2021). 

Queensland fruit fly is one of two species of pest fruit flies that have a major impact on pome fruit production in Australia. 

Queensland fruit fly quick facts 

• A native tephritid whose natural range has expanded southwards in the eastern states. It is now officially considered endemic to the Northern Territory, Queensland, New South Wales and Victoria. 
• Trapping to detect presence of adults and prediction of key life cycle periods will improve the timing and efficacy of control measures. 
• Monitoring traps use Cue-Lure (a synthetic parapheromone) as the attractant for male flies. 
• Methyl-eugenol is used in surveillance traps to detect presence of other exotic fruit fly species. 
• On-farm quarantine, orchard hygiene, monitoring and surveillance traps, and area-wide co-operation to manage host plants are critical to good control. 
• Protein is important for freshly emerged fruit flies to mature sexually and for females to develop eggs. Protein baits attract both sexes of immature fruit flies. They are not an attractant to sexually mature flies except for older females that have laid eggs and need protein to develop another batch of eggs. 
• Protein bait effectiveness depends on the type of protein, the toxicant added to the protein, the formulation (liquid or gel), placement and baiting timing. They are short-range attractants, so traps need to be placed no more than 6m apart and bait sprays should be applied as coarse drops. 
• Male annihilation technique is an attract-and-kill technique for males. They combine a pheromone and a suitable registered toxicant in blocks or pads, placed at medium to high density in orchards. 
• Traps baited with lures containing host plant volatiles are available for monitoring and mass-trapping. 
• Legislation in some states requires traps with sticky surfaces to be enclosed in mesh or another device to prevent access by small vertebrates such as lizards, native mice and birds. 
• Sterile insect technique (SIT) uses mass-release of sterile flies to suppress wild fly populations. 
• Cover sprays against fruit flies can decimate beneficial predators and parasitoids. 

The Queensland fruit fly (Bactrocera tryoni), also known as Qfly and QFF, has a red-brown thorax with distinct yellow markings, a dark brown abdomen and is around 6–8mm long (Figure 1). It infests over a hundred species of fruit and vegetables. Its natural range has expanded from rainforests in Queensland and northern NSW into commercial fruits and more temperate regions and it is now officially considered endemic to the Northern Territory, Queensland, New South Wales and Victoria. Sporadic outbreaks occur in South Australia, Western Australia and Tasmania.  

Figure 1: The Qfly has a red-brown thorax with distinct yellow markings and a dark brown abdomen. Photo: Viwat Wornoayporn, IAEA

The life cycle 

During warm weather in spring or early summer adult fruit flies feed and mate (1) (Figure 2). Adult flies feed on sweet exudates from plants, including nectar, as an energy source. They feed on protein from yeasts and bird droppings on leaf surfaces to mature sexually and for females to develop eggs. Mated females follow the scent of ripening fruit (or vegetables) and lay their eggs (2). Female fruit flies can lay 500 to 800 eggs during their lifetime. Eggs are white, banana-shaped, and are placed in a cavity in the flesh close to the skin of the fruit using the female’s retractable, needle-sharp egg-laying organ called an ovipositor (3). This results in a distinctive ‘sting’ on the surface of the fruit. In warm weather, the eggs hatch in two to four days. Development of larvae (maggots) takes six to eight days in summer. Maggots have cutting jaws which allow them to cut fruit into pieces small enough to swallow. They tend to chew and create tunnels which lead toward the centre of the fruit. This chewing introduces bacteria and fungi which in turn result in the fruit developing severe internal rot. Fruit may appear perfect from the outside (4). Infested fruit often falls to the ground. When the maggot has completed growing it chews its way out of the fruit and burrows into the soil (5).  

In the soil, larvae become inactive and develop into oval, brown pupae in which the adult fly develops. Qfly will not survive through winter in this pupal form. The activity of fruit flies depends on temperature. Although development and life cycles slow, Qfly can exist as adults during winter in warmer regions.  

Figure 2: Key life cycle stages of Qfly. Source: Hetherington S and Monroe A (2009) Integrated pest management for Australian apples & pears, Industry & Investment NSW and Apple and Pear Australia Ltd. Orange, NSW.

Damage

The egg-laying sites on pome fruit are indicated by punctures called stings. The female causes these with her needle-like ovipositor that she inserts into the fruit to lay her eggs. Stings are more obvious on pale, smooth-skinned apple cultivars and green-skinned pears. The type of damage caused by fruit fly larvae varies with the type and maturity of the fruit, the number of larvae in it and the weather. As the larvae feed on the flesh of the fruit, various yeasts and bacteria develop and cause further breakdown of the flesh. If the flesh is hard or immature the larvae form a network of feeding channels that eventually leads to internal decay. Heavily infested fruit will eventually fall to the ground and the mature larvae will crawl out and burrow into the ground to pupate.  

Figure 3: Qfly larvae form a network of feeding channels inside the fruit, which leads to internal decay. Photo: Ben Bobby

Management and spread 

In-field management controls prior to the fruit becoming susceptible to attack are essential. Control measures listed in the Qfly quick facts box are further detailed in the IPDM Manual.  

The main means of fruit fly dispersal is through transport of eggs or larvae in infested fruit. Fruit flies are often transported over large distances by travellers. Domestic quarantine limits distribution between states and limits Qfly from establishing in fruit fly-free regions. These quarantine zones are regulated and monitored by state government departments.  

Orchard hygiene  

On-farm quarantine protocols to prevent visitors, contractors and staff bringing potentially infested fruit onto the property is a good first step in management of any pests or diseases. Obvious signage at all entry points will reinforce the message. Businesses that pack or store fruit for other growers need to ensure that they have strict guidelines in place that either impose standards for delivery of fruit or deal with ways to process substandard and/or infested fruit, including disinfection of bins.  

It is important to remove and destroy waste fruit which is, or could become, infested with fruit fly. Fruit which has fallen or is left hanging after harvest should be removed and destroyed. Remember that even fruit which appears perfect may harbour infestations so be conservative and treat all unharvested fruit in this way.  

Any host plants that are unwanted or regularly remain unharvested should be removed and destroyed. This includes trees from around sheds and houses, along boundaries and irrigation channels, and roadsides (if permitted by local by-laws). These measures will also help with management of other pests such as codling moth, oriental fruit moth and Carpophilus beetles, and diseases such as scab.  

Continual monitoring for signs of Qfly is an important component of an integrated pest and disease management plan. More information on Qfly and its control can be found in the IPDM Manual. 

What R&D is underway?  

The PIPS 4 Profit Pest and disease management (AP22001) project is studying the feasibility of fruit fly biological control in apple and pear growing regions impacted by Qfly and Medfly. The study includes trial releases of the parasitoid Diachasmimorpha kraussii for the control of Medfly in Western Australia; assessment of the conditions that favour establishment of parasitoid populations (for example, release numbers and provision of resources in inter-row vegetation); and augmentative release strategies that are efficacious and economically feasible. 

Further information  

The IPDM Manual for Australian Apples and Pears is your primary industry resource for the identification and management of pests and disease. To download a copy of the IPDM Manual visit extensionaus.com.au/ozapplepearipdm/ipdm-manual-for-apples-and-pears. 

Acknowledgement  

The PIPS 4 Profit Pest and disease management (AP22001) project has been funded by Hort Innovation, using the apple and pear research and development levy, contributions from the Australian Government and co-investment from Agriculture Victoria. It is supported regionally by the Tasmanian Institute of Agriculture, Pomewest and NSW Department of Primary Industries and Regional Development. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture. 

This article was first published in the Winter 2025 edition of AFG.