Sterile Insect Technique and the emergence and release of sterile flies
Sterile Insect Technique (SIT) is a biological control method. It is used in conjunction with other control methods such as foliar baiting and crop hygiene to create Fruit Fly Free Areas, or Areas of Low Pest Prevalence. It is an area-wide technique and must be applied over large areas to be effective. SIT is environmentally friendly and it can help reduce broad-spectrum chemical treatments. This makes it very acceptable to export markets, which increasingly focus on ecologically compatible, sustainable production techniques that reduce or eliminate pesticide residues.
The SIT used as part of the Carnarvon Medfly eradication pilot project relied on mass produced sexually sterile insects decreasing the wild population. This resulted in sterile mating and a population decrease. Sterile Medflies can only be differentiated from wild Medflies under ultraviolet light.
A purpose-built emergence facility for sterile Medfly was constructed on the DPIRD research station in Carnarvon (opened by the then Minister for Agriculture in April 2016), and has since been in use trialling and continuously improving sterile Medfly emergence and release technologies. Approximately 4-5 million sterile flies per week were released.
Worley towers (physical structures used to ensure successful, bulk emergence of the flies) have been used in the Carnarvon emergence facility; the first application of this technology in Australia. With the Worley towers, flies are able to develop to maturity prior to release in a smaller area than alternative options.
An innovative, custom-built mobile fly release machine was built in Queensland specifically for use in the Carnarvon medfly eradication project. Key features of this machine are improved mobility and access, GIS tracking capability, capacity to keep the flies chilled, and that it takes a single person to do the task rather than the 3 previously required.
Legislation and regulatory instruments
The Piloting new techniques to control and eradicate Mediterranean fruit fly in Carnarvon project operates under the provision of the BAM Act 2007. Medfly was declared a Category 2 declared pest (i.e. an eradication target) in the area of the Shire of Carnarvon within a 15km radius from the south west corner of Bibbawarra Rd and North West Coastal Highway on 28th August 2015.
Trapping and monitoring
A trapping and monitoring program is one of the project’s key strategies to reduce wild Medfly numbers to a level where sterile fly release can be effective. A series of 50+traps were deployed in mid-2015; 40+ across Carnarvon plantations and 10+ in the town of Carnarvon to collect information about wild Medfly numbers and distribution over time.
The traps have been checked fortnightly since then, and wild Medfly numbers in each trap recorded and tracked. Lynfield traps (with a lure and insecticide system to attract and kill) were used from the start of the trapping program to July 2016; and Jackson traps (a disposable trap with an active glue-lined inner surface to trap insects) have been used since August 2016. This level of trapping and monitoring allows clear identification of ‘hot spots’ of high Medfly prevalence in real time. Results are then used to:
- Inform baiting scheme operations to target areas for the following fortnight.
- Direct the project communications and engagement officer / compliance officer to work with ‘hotspot’ growers to improve crop protection and hygiene practices.
- Enable more strategic trap placement.
Baiting scheme
A foliar ‘bait and kill’ program is another of the project’s key strategies to reduce wild Medfly numbers in plantations to a level where sterile fly release can be effective. Two baiters are employed through the Carnarvon Growers Association Recognised Biosecurity Group to ‘bait and kill’ Medfly; spraying an attracting lure and chemical control combination onto foliage in plantations. As a priority the baiters target any hot spots identified through the fortnightly trapping and monitoring program.
You can help by employing Medfly control methods appropriate for your backyard or control methods appropriate for commercial growers. It is also important to know how to identify a medfly infestation and to learn about this pest’s biology.