According to the 2015/16 Australian Horticulture Statistics Handbook, Australia’s horticultural production is valued at over $11 billion, and over $5 billion of this is potentially affected by fruit flies. Australia is also a nett exporter of fresh fruit and vegetables and approximately $1 billion of these exports are potentially impacted by fruit flies. Therefore, being able to ship fresh fruit and vegetables within Australia and overseas while managing concerns about fruit flies is vital.
Regions that import fresh fruit and vegetables impose biosecurity conditions to manage the risk that a damaging pest or disease will be on an imported commodity and subsequently establish. These conditions are only applied to extent necessary to protect plant life and health, but can vary between regions.
So, while Australia’s horticultural producers have an enviable reputation of growing some of the world’s best and cleanest commodities, an importing state or country might require that imported fruits and vegetables be treated or to satisfy some other safeguard.Given the importance of fruit flies as pests, these measures can be particularly rigorous.
Starting in the orchard
While biosecurity conditions are sometimes thought of as additional requirements, good pest management in the orchard, field, or glasshouse is a critical foundation. Effectively managing fruit flies prior to harvest helps to ensure there is a high quality crop for discerning markets and also minimises any chance that pests will be detected during a quarantine detection. Even though these pests might not be viable or be of biosecurity concern, they can lead to costly delays.
A mainstay for managing pests of biosecurity concern for many years has been the use of post-harvest treatments. These can involve a wide range of options such as extended cold storage or fumigation, but are typically characterised by using a single treatment or step with a known and very high level of efficacy. The benefit of such treatments is that they do not rely on knowing the prevalence of a given pest and can be relatively simple to develop. However, because these treatments dont consider pest prevalence they might be might more rigorous than needed. The high levels of efficacy also means that very large trials needs to be undertaken. Thus developing these treatments can cost in the hundreds of thousands of dollars or more and involve a multi-year research program.
Cold treatment is a treatment used extensively for Australian produce. It involves storing fruits or vegetables at low temperatures for an extended duration to kill any insects present. For most fruit flies maintaining a temperature below 3°C for 16–18 days will kill any eggs or larvae present. It requires no chemicals, but is not suitable for all commodities.
Heat treatment is especially used for tropical commodities and involves heating fruit in a water bath or enclosed chamber to raise the temperature inside the fruit to around 45°C for around 20 minutes.
Fumigation has been used for many years and involves enclosing the fruits or vegetables in an chamber and applying a gas that is toxic to insects. The fruits and vegetables are then ventilated to remove any residue of the gas. Fumigation can be a favoured treatment as it is simply to apply and usually does not require any specific heating or cooling.
Systems approaches – a new way forward?
An alternative to single step post-harvest treatments are “systems approaches”. Put simply, a systems approach is a number of independent measures or actions that cumulatively provide the level or protection from a specific pest or disease that an importing country or region requires.
The potential benefit of pursuing a systems approach is the flexibility to consider the prevalence of fruit flies in a specific location and how a wide range of practices that might be standard practice can provide confidence that viable pests will not be in exported fruits and vegetables. Systems approaches could also allow exports without expensive, time consuming, or damaging treatments.
However, developing and approving systems approaches isn’t necessarily a straight forward process. As there are two or more points at which fruit flies are being controlled, there may be increased costs or complexity in the pest management system. These issues need to weighed up to compare the merits of a systems approach versus a single point treatment.