About Queensland Fruit Fly
Over the last several years, Queensland Fruit Fly (often abbreviated as QFF or Qfly) has become a serious pest in an increasing number of Melbourne suburbs. If you’re growing any kinds of fruit plants in the Melbourne area, it’s only a matter of time before you’ll need to deal with this serious threat to your crops. Here are answers to a range of commonly-heard questions regarding Queensland Fruit Fly. We hope this will help readers to understand this pest and the risks it poses, to learn about ways of dealing with it, and to find further information.
What do QFF flies and maggots look like?
Mature Queensland Fruit Fly QFF maggots infesting a nectarine
Queensland fruit flies (Bactrocera tryoni) are reddish-brown in color, have distinct yellow markings on their bodies and nearly transparent wings. They are sometimes mistaken for wasps, which they resemble. Mature QFF usually measure about 6mm to 8mm in length, and hold their wings horizontally when walking.
QFF larvae/maggots are white or cream-coloured and can be up to about 9mm in length. They are wedge shaped, and slightly plumper at the tail end. Mature larvae have a visible black feeding hook. Infested fruit can contain as many as twenty larvae.
What damage is caused by QFF?
After mating, QFF females make a tiny hole into fruits and deposit their eggs under the skin. These eggs hatch larvae, which proceed to consume the flesh of the fruit, causing it to decay and drop prematurely. Affected fruit often appear completely normal, despite the interior having been converted to a useless and inedible pulp by the ravenous QFF larvae within. Up to 100% of exposed fruit can be destroyed as a result of QFF infestation.
QFF can affect almost all commercial fruit crops – with the exception of pineapples, evidently owing to their high acidity level. Control measures are also difficult and expensive to implement effectively. As a result, QFF are the most costly horticultural pest in Australia, annually causing about $30 million damage to our crops.
What should I do with fruit which are infested with QFF larvae?
Fruit infested by QFF are usually rendered completely inedible. Recommended methods of killing QFF larvae in infested fruit include boiling, baking or microwaving the fruits containing them, or bagging them in the freezer for at least three days. Once processed this way, the remains should be discarded in general rubbish – not with green waste or with your compost.
But isn’t QFF a problem only in Queensland?
The Queensland Fruit Fly is native to subtropical coastal Queensland and northern New South Wales, and it prefers humid and warmer climates. Queensland fruit fly now exist in the Northern Territory, Queensland, New South Wales and Victoria. They are most widespread in the eastern Australian states, but have also now been reported New Caledonia, French Polynesia, the Pitcairn Islands, and the Cook Islands. And over the last decade or so, a number of quarantines have been put in place in Auckland when imported QFF have been detected there.
The similarly-destructive Mediterranean fruit fly (usually abbreviated as "Medfly") is a serious pest in southwestern Western Australia. But so far, there have been no serious outbreaks of QFF there, on account of the large arid zone between eastern and western Australia and nationally coordinated surveillance and control.
Is climate change a factor in the spread of QFF?
Rising temperatures due to climate change have contributed to the spread of QFF to other regions of Australia and Polynesia. QFF can tolerate very high temperatures, but over time they have adapted to survive in cooler temperatures and at higher altitudes. These behaviours suggest that damage caused by these insects is likely to increase in the future.
How does the QFF lifecycle work?
QFF numbers tend to increase in spring, when temperatures become warmer and suitable host plants, such as apricots, apples, berries, tomatoes and capsicums, become available.
The times given here for each phase of the QFF lifecycle can vary, depending on temperature and other conditions. From the age of about two weeks, adult QFF females can mate (typically at dusk) and deposit about seven eggs through a fruit puncture or “sting” into a fruit. A single female QFF may deposit up to 100 eggs per day. Females often oviposit into punctures made by other fruit flies, which can result in many eggs occurring in a single cavity of a fruit.
About three days after laying, QFF eggs hatch into larvae or maggots which eat toward the centre of the fruit, causing it to rot. After two to four weeks, maggots grow to their full size of about 9 mm in length, by which time the fruit often has fallen to the ground.
The maggot then chews its way out of the remaining fruit into the soil and enters the pupal stage of development. Depending on temperature, this stage lasts between one and four weeks. These then hatch from the soil as mature adult flies, typically near the end of the summer season.
Unlike other fly pests, QFF do not breed continuously, but overwinter in their adult stage and can live for many months. Up to four or five overlapping generations may occur annually. Adult flies are reliant upon leaf surface bacteria as their major source of protein.
What measures are used to reduce the impact of QFF?
In commercial orchards, QFF was commonly controlled by the application of the pesticide chemicals dimethoate and fenthion until about ten years ago, when they were suspended from use because of safety concerns. As a result, modern QFF reduction or elimination methods have been developed, based on studies of this pest’s behaviour. Farmers in affected regions are encouraged to use lures such as pheromones, food attractants, host mimics, or colour attractants. Recommended killing mechanisms often involves pesticides, liquid traps in which the pest drowns, or sticky traps from which the pest cannot escape.
Additional control measures include using fine netting to protect individual fruit or entire trees. Traps and lures for killing or monitoring purposes are commercially available.
How can I reduce the impact of QFF on my own garden and neighbourhood?
The control methods described above are quite time- and energy-intensive. So if QFF is an issue in your area, you’ll probably want to find ways to deal with it with minimal effort. Things to try include:
- Reduce the number of fruiting plants in your garden
- Try growing fruits which ripen early in the season, when QFF numbers tend to be lower
- Plant dwarf fruit varieties and learn to prune them to keep them small, to make them easy to inspect, net and harvest
- Set commercial or homemade QFF traps or lures. A range of suitable commercial products are available. You can also try making homemade male QFF traps – recipes for these using protein and sugar baits abound online, but note that these require frequent refreshing to be effective.
- Collect fallen fruit immediately, before larvae can emerge and burrow, and deal with it as described above
- Be circumspect about sharing fruit and vegetables with neighbours and friends
- Avoid transporting harvested fruit to other areas
- Pay attention to which varieties of fruit are more or less QFF resilient, and plan accordingly. For example, some apple and tomato varieties clearly vary in their susceptibility
- Run chickens under susceptible fruit trees so they can clean up fallen fruit and consume larvae and emerging QFF adults
- Discuss QFF control and the responsible handling of affected fruit with your friends and neighbours, especially if they are growing susceptible plants
What is the Heritage Fruits Society doing regarding QFF?
Some (but not all) varieties of the apples in the HFS heritage collection at Petty’s have been attacked by QFF this year. This suggests that some varieties are more resistant than others, knowledge we can usewhen we advise the public of which apple varieties they should grow.
In the meantime, the Society is aiming to help inform as many people as possible about the challenges QFF pose to fruit growers and others, and measures they can take to sensibly and effectively deal with this dreadful pest.
Information card HFS distributes to all users of fruit from the HFS Heritage Block
Is it mandatory to report QFF sightings?
It is no longer required (in suburban Melbourne, at least) to notify local or state authorities if you discover live Queensland fruit flies. However, some councils (e.g. Darebin) provide a link on their website where you can report sightings if you wish. Alternatively, you can report sightings to the National Fruit Fly Council at https://www.preventfruitfly.com.au/report-fruit-fly/ .
How can I learn more about QFF?
Here are some good information sources we’ve seen:
Nillumbik Council's pest information page (with videos): https://www.nillumbik.vic.gov.au/Explore/Environment/Natural-environment/Animals/Pest-animals
Darebin Council’s QFF information video: https://www.youtube.com/watch?v=pwXZx79JWDw
Darebin Council’s website page regarding QFF: https://www.darebin.vic.gov.au/Waste-and-environment/Sustainability/Gardening/Queensland-fruit-fly
More detailed information about QFF can be found here:
https://agriculture.vic.gov.au/biosecurity/pest-insects-and-mites/priority-pest-insects-and-mites/queensland-fruit-fly/controlling-queensland-fruit-fly-in-home-gardens
https://en.wikipedia.org/wiki/Bactrocera_tryoni
https://mysmartgarden.org.au/resources/habitat/queensland-fruit-fly/