Phytosanitary measures are often required for imported commodities to prevent the introduction of quarantine pests. Such measures need to be appropriate for a specific commodity and effective against the quarantine pests of that commodity.
APPPC member countries cover a wide climatic range and the many different pests present, including fruit fly species, have different geographic distributions and host ranges. For this reason, there may be differences between countries in their phytosanitary requirements for the importation of fruit fly host commodities.
Phytosanitary measures are normally developed on a country/commodity/ pest specific basis through a process of bilateral negotiation between the National Plant Protection Organizations (NPPOs) of the importing and exporting countries.
In developing phytosanitary management options, APPPC member countries should take note of the principle of equivalence and therefore be prepared to use different treatments that are equivalent. For example, alternative phytosanitary management options such as cold disinfestation treatments, chemical disinfestation treatments, irradiation, area freedom, systems approaches, or combinations of the above may be appropriate for consideration of equivalence where feasible.
Among the above measures, heat treatment is regarded as one of the measures that is environmentally friendly and free from residues.
The purpose of the standard is to provide a sound basis for APPPC member countries when developing heat disinfestation treatment against quarantine fruit flies in host commodities. It is intended to facilitate trade of the commodities by member countries
Fruit fly species associated with the country/commodity combination should be identified by a pest risk assessment. Information on the status of fruit fly pests in the importing and exporting countries and on host preferences should be comprehensive and well documented. Where not available, research should be undertaken.
A fruit fly can be listed as a quarantine pest for a country only if it meets the criteria of the definition of a quarantine pest.
Heat is commonly used as a physical disinfestation treatment for fruit flies. Heat treatments include hot water dips, vapour heat treatment (VHT) and high temperature forced air (HTFA).
Factors influencing the selection of a treatment include:
impact on the commodity
effectiveness on the target pests
post-harvest shelf-life
feasibility (including cost)
requirements of the importing country.
Heat disinfestation options are best developed on a case by case basis for each country/commodity/pest combination using the general guidelines described in this standard.
Where more than one quarantine fruit fly species is identified for a specific country/commodity combination, it is necessary to determine which stage of which species is the most tolerant to the treatment that is being proposed. Any large scale confirmatory testing that is required can then be restricted to this species and life stage.
It is important to seek relevant technical expertise (e.g. from biometricians, entomologists) and to consult the relevant scientific literature to ensure that laboratory tests and trials are designed and conducted appropriately. With all tests and trials, untreated controls are required.
Where new treatments are to be developed, it is appropriate for the relevant NPPOs to agree bilaterally on experimental design including the quantity and quality of data required to meet the importing country’s requirements.
Experimental fruit
Fruit for use in disinfestation experiments should be:
identified botanically, including details of variety or cultivar if this may impact pest response to the treatment
free from any chemical treatment before its use in the trial
described in relation to stage of maturity, size, shape and quality
infested at a susceptible stage
in normal commercial condition.
Experimental insects
The following points must be considered when insects are used in heat disinfestation experiments:
the insects should be identified taxonomically; it may be necessary to test for differences within the pest population
reference specimens should be made available
the laboratory colony should be founded from an appropriate source, preferably from a large quantity of field infested host fruit, ensuring that other species, parasites and disease are removed. This can be aided by rearing different fruit fly species in different rooms.
the laboratory colony should be founded from appropriate numbers of individuals (100-1 000)
the laboratory colony should be appropriately handled during its rearing history to ensure peak vigour for the duration of the experiment
laboratory colonies should be regularly refreshed with new wild flies so that the genetic diversity of the laboratory specimens can be considered to be representative of the population in the field
the health of the laboratory colony should be regularly checked by monitoring such factors as per cent hatchability, mean pupal weight, developmental time, eclosion percentage, sex ratio of eclosed flies and fecundity of each generation
methods and conditions of rearing should be carefully documented.
Infestation of experimental fruit
Experimental fruit can be infested through natural (this is preferred) or artificial means.
If not known, it may be necessary to conduct studies on the fruit to determine the most susceptible stage and conditions for infestation.
Natural infestation involves exposing the experimental fruit to ovipositing females of experimental fruit fly species for a set period of time. This is usually done in a laboratory cage under strict conditions. Care should be taken to ensure that the population of ovipositing females in the cage at peak vigour (see 4.2.1.1), the number of flies per cage, the exposure time, the number of fruits per cage and the experimental conditions are adequately controlled.
The time allowed for oviposition in the fruit should be kept as short as possible.
Artificial infestation involves placing the experimental species into the trial fruit. A know number of eggs or larvae of the appropriate stage are placed directly into the fruit using a method that is biologically appropriate and minimizes damage to the fruit and insects. Untreated controls are required.
Determination of the most tolerant fruit fly species
The most tolerant species should be identified through small-scale trials by determining appropriate dose response curves. Small-scale trials should be conducted using replicates of fruit fly individuals (each replicate should have at least 100 fruit fly individuals).
“Naked” (in vitro) insect trials are appropriate to determine the most tolerant species. This involves taking eggs and differently staged larvae of different species, dipping them directly into hot water (or appropriate heat source) and then transferring them to an appropriate rearing medium. Care should be taken to select appropriate number of insects, treatment levels and exposure times.
Thermometers and other measuring devices should be accurately calibrated.
Determination of the most tolerant fruit fly development stage
The most tolerant development stage of the fruit fly should be identified also through small-scale trials using artificially or naturally infested fruit by determining appropriated dose response curves. This can be done by exposing the experimental fruit to ovipositing females of the experimental fruit fly species for a set of period of time to achieve the most tolerant stage. Small-scale trials should be conducted using replicates of fruit fly individuals (each replicate should have at least 100 fruit fly individuals).
In addition, importing countries are likely to require efficacy to be determined by this type of in vitro trials.
For the determination of the heat disinfestation treatment, the experiment should use the most tolerant developmental stage of the most tolerant fruit fly species.
Treatments of infested experimental fruit would normally be undertaken first on a small scale. Small-scale trials should be conducted using 3 000-5 000 individuals. Following this, a confirmatory test in large-scale trials would normally be required to establish the technical validity of the treatment and to demonstrate the required level of efficacy. At least 30 000 fruit fly individuals should be used in a large-scale trial.
It is necessary to demonstrate that the treatment unit has adequate heating, cooling, insulation, humidity and thermostat controls. In the case of Vapour Heat Treatment and High Temperature Forced Air units, the coolest points should be determined based on a temperature map of the inside of the unit. Heat sensors should be located at these points and placed in the largest fruit in the treatment batch. The rate of heating and cooling should be accurately recorded with measurements taken at appropriate pre-determined intervals (e.g. every 2 minutes).
Treatment units and facilities may need to be approved or certified by the NPPO before treatment commences. It may be agreed between the NPPOs of the importing and exporting countries for officials from the importing country to observe the trials. NPPO officials should ensure that the temperature specifications are met. The owner/operator of the facility is responsible for its efficient operation.
Treatment facilities should be located in a secure area to prevent reinfestation of treated fruits (post-treatment security).
Treated experimental fruit and untreated controls should be held in a secure location under physical conditions that are favourable for the fruit and for the survival of the insect species.
Pupae should be retrieved under appropriate conditions at an appropriate time. All fruit should be examined to find any remaining larvae.
The level of efficacy required by importing countries for individual phytosanitary treatments should meet the ‘appropriate level of protection (ALOP)’ of the importing country. ALOP is defined by the WTO in the SPS Agreement as:
“The level of protection deemed appropriate by the (WTO) Member establishing a sanitary or phytosanitary measure to protect human, animal or plant life or health within its territory.”
WTO Members have the sovereign right to determine their own ALOP. The ALOP may therefore vary from country to country but it should be based on scientific justification and applied consistently within each country.
NPPOs generally require a very high degree of efficacy for treatments developed against quarantine pests such as fruit flies. Often, lengthy, large-scale trials are required to show that individual treatments are highly effective against the target pest on the commodity.
Traditionally, many of the treatments developed against fruit flies have used probit 9 mortality as a measure of treatment efficacy. However, it is a measure of mortality. Pest risk, on the other hand, should be recognized as being related to the number of survivors and therefore the initial infestation rate should be considered in determining whether the level of efficacy corresponds to the ALOP.
To attain the level of protection to deal with the level of risk associated with fruit fly pests, other factors that may reduce the risk of entry and establishment such as the likelihood of infestation in the imported commodity, survival rate, reproductive potential or establishment potential should be considered. In addition, in cases where the natural rate of pest infestation in the field is low and the chances of survival and reproduction are poor, the probit 9 standard could be too stringent. Some countries are proposing a less severe treatment combined with modifications in packing, distribution, and inspection. Recognizing that treatments may range in severity depending on the risk allows expanded use of controlled atmospheres, systems approaches, and other treatments, which have in the past not met probit 9 requirements.
The heat disinfestation treatment could also be used as a component in a ‘systems approach’ or combination treatment (see ISPM No. 14 The use of integrated measures in a system approach for pest risk management).
Before commercial trade commences, further large-scale trials may also be required to confirm that the treatments are not only technically sound but also commercially and operationally feasible. The treatment system should be reliable under commercial loading methods and likely product distributions.
Where the evaluation exercises are successful, both parties need to endorse the treatment. The approved treatment may then be part of the trade access agreement between the two countries for the commodity involved.
All records and data should be kept and made available for audit by NPPO officials if this is required.
