This project developed female fruit fly lures to improve pest surveillance technology. These will aid in the detection and control of fruit fly species not attracted to the currently deployed male lures and will enhance surveillance capability for exotic fruit fly species.
Research outcomes
Fruit flies are significant pests of horticultural crops worldwide. In Australia there are two fruit fly species of economic concern; the introduced species Ceratitis capitata (Mediterranean fruit fly; Medfly), which is present mainly in the south-west corner of Western Australia, and the endemic species Bactrocera tryoni (Queensland fruit fly; Qfly), which is found along the coastal fringe of the eastern states (Queensland, New South Wales and Victoria).
Australia maintains a number of certified fruit fly free areas, including South Australia, Tasmania and the fruit Fly Exclusion Zone on the Victoria/New South Wales border. Maintaining these areas free from fruit fly and keeping exotic species of fruit fly out of Australia is critical to retaining access to our export markets. Surveillance using fruit fly traps is the principal tool used in defence against invading pests, but there are some fruit fly species that do not respond to the male lures typically used in surveillance programmes. Development of improved lures for detection of female fruit flies would improve our surveillance capability and was the primary aim of this project.
Two prototype lures were developed: a gel lure and a dry lure. The efficacy of these lures was investigated in comparison to the standard liquid protein lure (for Bactrocera species) and the three-component BioLure® (for C. capitata). Results from the trials indicated that there are significant advantages to be gained by replacing the standard liquid protein lure with a gel lure for surveillance purposes. The gel lure developed and tested in this project was found to maintain its attractancy under a range of climatic conditions for a period of 6-12 weeks, compared to only one week for the liquid lure. It was easily dispensed in traps, did not have an unpleasant odour and captured much fewer unwanted insects, such as blowflies.
The condition of fly specimens removed from traps containing the gel lure was markedly better than those removed from traps containing the liquid lure. However, the efficacy of the gel lure compared to the liquid lure was variable depending on the climate, fly species or crop. Sometimes trap captures were comparable (e.g. D. pornia captures at Kulnura, NSW) and sometimes significantly fewer flies were captured in traps containing the gel lures (e.g. B. tryoni captures at The Rock). Gel lure did not compare favourably with BioLure® in field trials in WA for C. capitata or native Bactrocera species other than B. jarvisi. Unfortunately, the prototype dry lure consistently performed poorly, probably as a result of rapid volatilisation of attractants.
Experiments conducted in WA demonstrated that the three-component BioLure® is the most effective attractant for C. capitata, while orange ammonia lure performed best for Bactrocera spp. A significant finding was the effectiveness of 70% propylene glycol (PG) as a killing agent for use in traps with dry lures, such as three-component BioLure® and male lures, Capilure® and Cuelure. Greater numbers of flies were repeatedly found in traps containing 70% PG as the killing agent compared to traps containing malathion and/or dichlorvos (DDVP). The increased attractiveness of the lures when combined with 70% PG could be due to the presence of liquid, particularly in dry climates where flies need to seek out water. PG is a preferred killing agent, as it has relatively low toxicity compared to the commonly used organophosphate insecticides, and could be used in organic orchards.
Further improvements to the ingredients in the gel lure, or perhaps the development of a more effective trap that disperses lure odour over a greater distance, could see liquid lures being replaced in future. In the meantime, the superior efficacy of the liquid protein lure or orange ammonia lure means that these probably still remain the preferred lures for use in surveillance systems for Bactrocera species, and three-component BioLure® the preferred lure for use in surveillance systems for C. capitata. Where liquid protein lures continue to be used for surveillance, it is recommended that a stainless steel mesh insert and DDVP pest strip be used with the McPhail trap to improve the serviceability of traps and preserve the integrity of fruit fly specimens. Where three-component BioLure® is used in Chempac/Suterra traps, propylene glycol may be a suitable alternative to DDVP pest strips, reducing the risk of accidental poisoning where traps are used in urban areas and facilitating the use of traps in organic orchards.
Research implications
The most critical implication of the data produced in this project is that the food-based attractants for female fruit flies, particularly Bactrocera spp., are not consistently effective lures. The laboratory data produced here indicates that generally less than 20% of protein-deprived Bactrocera tryoni (Queensland fruit fly) are attracted to a protein lure. If flies had been fed protein prior to the trial, they were even less attracted to a protein lure, with typical captures of less than 3%. This means that the likelihood of capturing a female fruit fly in a trap with a protein-based lure is very low, particularly if the population is low, as would be expected with an exotic incursion. Under the experimental conditions used here, the proportion of Ceratitis capitata (Mediterranean fruit fly) attracted to three-component BioLure®, which is based on food attractants, was considerably higher, up to 75%. In this instance it is clear that this lure could be used effectively for surveillance of areas free from C. capitata, such as eastern Australia, and as a tool to reduce female populations in affected areas.
The low attractancy of protein to Bactrocera spp. has other impacts on fruit fly management. Apart from being used for lures, protein is also incorporated with insecticide and used as fruit fly splash baits. Baits are applied to crop foliage or surrounding vegetation to attract the fruit flies to feed. The data produced here indicates that the flies are likely to find the baits by chance, particularly since baits are applied to sites where fruit flies are known to rest and forage.
The sensitivity of surveillance lures can be greatly enhanced through the addition of 70% propylene glycol (PG) as a killing agent. Data clearly showed that combining PG with male lures increased the number of flies captured. This small adaptation can immediately improve the sensitivity of existing surveillance grids, particularly where low populations are likely to be detected (e.g. shipping ports, Torres Strait islands and other areas covered by the Northern Australia Quarantine Strategy). However, because of the liquid nature of PG, this change would increase the level of maintenance that these traps would require.
The modification of McPhail traps to include a stainless steel mesh insert when using liquid lures would improve the serviceability of these traps and markedly improve the quality of fly specimens. However, this modification would require the use of dichlorvos (DDVP) as a toxicant.
Acknowledgements
Mrs Jane Speijers (DAFWA) provided invaluable guidance in the planning of orchard trials and in statistical analyses of the Western Australia component of the project.
Thanks are due to the following DAFWA staff who assisted with field work at various stages of the project: Ms Charlotte Butler, Ms Helen Collie, Ms Linda Fernihough, Ms Emma Mansfield, Ms Valentina Mella, Ms Sandra Wellington and Ms Candice Wong with work in the south west. Thanks are due to the DAFWA staff in Kununurra including Penny Goldsmith, and specifically Ms Natalie Bort who assisted in the set up and experimental work in Kununurra with considerable diligence invaluable for the completion of this work.
In NSW, appreciation is shown to I&I NSW staff who assisted with field trials: Mr Matthew Pearse, Mr David Cruickshank, Mr Vincent van der Rijt and Ms Dorothy Evans. Mr Ross Hitchcock is also acknowledged for his generosity in allowing us to use his orchard for field trials.
