Queensland Fruit Fly (Qfly; Bactrocera tryoni) is native to the wet tropics of Queensland. As more irrigated horticultural crops have been grown along the Eastern Coast of Australia, this species has spread southwards. In Queensland, New South Wales and Victoria citrus growing regions Qfly is a managed pest. Qfly awareness programs are active in Victoria, with the Murray Valley Fruit Fly Program working with communities to improve management of the fly in home gardens near major Sunraysia horticultural production areas. In South Australia, Qfly is under containment and eradication.
The Qfly lifecycle
After mating only once, a female fly can lay up to 500-2000 eggs. After oviposition of the egg under the citrus fruit rind, a larva will hatch within 1-2 days. Young larvae will burrow further down into the fruit. The larvae grow through three instar stages over 6-20 days depending on the fruit host and climatic conditions. Mature larvae migrate back to the fruit surface and drop to the soil or leaf litter below the tree to pupate. After 8-15 days as a pupa an adult fly will emerge. After finding a meal of protein and carbohydrate, young adults will mate within 4-10 days of emergence. Under optimal climate conditions (11.5°C-36°C) eggs can develop into adult flies within one month, leading to rapid population growth at certain times of the year.
Seasonal occurrence of Qfly
Qfly populations expand and retract throughout the year according to local climate conditions. It thrives in warm and moist climates. However, even in drier climates like the Murray Valley Qfly can survive and rapidly reproduce due to the large number of host crops and high rates of irrigation in the region, which form ideal microclimates to support fly populations. At certain times of the year, populations will retract due to extreme heat and frost.
Past research has indicated that survival from egg to adult is unlikely if daily maxima prevail in the region of 38–40 °C for more than 7 days. However, Qfly is adept at finding microclimate refuges to survive extreme conditions, although reproduction will slow down and populations will retract in size during this time. Fruit fly numbers tend to increase, usually in spring, when temperatures are warm and there is continued availability of suitable host plants.
Monitoring & management of Qfly
Monitoring
Many brands of traps are available for Qfly monitoring. They usually contain an attractant and either a small dose of pesticide or a liquid in which the fly drowns. Monitoring lets you know when (and where) fruit fly populations are building up and shows you whether treatment has been effective. Traps should be monitored to detect spikes in populations. Check traps regularly. If you find Qfly in traps, that means Qfly are still in or near your orchard, so you should continue with regular bait sprays.
Management
In addition to monitoring, management should include proactive chemical control, mainly through regular baiting, which has minimal impact on beneficial insect populations.
Baiting: A Qfly bait is made of protein (to attract the flies) and insecticide (to poison the protein bait). Some growers add gum to the mix to extend the effectiveness of the bait. Apply a weekly bait spray to any orchard areas that still have fruit. Direct the bait spray to the trunk or foliage at the skirts of trees (avoiding fruit). Baiting should be proactive and begin in early Spring in order to catch male and female flies after winter emergence and before mating begins and should be carried out weekly.
Cover spraying: If fruit has sting marks, or numbers of flies in traps increase, a cover spray may be warranted. Follow the product label Directions for Use. Wet the canopy to run-off.
Post harvest treatment: If fruit remains on trees or the ground after harvest and there has been Qfly activity in the season, consider a post-harvest application.
Read this fact sheet for more details about Queensland fruit fly management and view the videos below to hear from some Murray Valley growers about how they bait for the fly.
Qfly eradication – Riverland Fruit Fly Response
In response to the detections, the Riverland Fruit Fly Response program has been implemented, focusing on intensive surveillance, baiting, and eradication efforts. Fruit growers in the Riverland are required to adhere to strict control measures, including regular monitoring of their orchards, implementing baiting and trapping programs, and ensuring that all harvested fruit is treated appropriately to prevent the spread of the pest. Additionally, movement restrictions have been placed on fruit and vegetables from affected areas to prevent the spread of the Queensland fruit fly to other regions. These measures are critical to protect the Riverland's horticultural industry and to regain and maintain its PFA status.
The outbreak end date is published as 23 December 2024. The anticipated outbreak end date is calculated using an agreed method under the National Fruit Fly Management Protocol. The outbreak end date is dependent on there being no fruit fly detections in red outbreak or yellow suspension areas for at least 12 weeks.
More information about the Qfly response in South Australia can be found on the Primary Industries & Regions South Australia website:
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