Irradiation as a Quarantine Treatment: Research Protocols (Guideline III)
Irradiation as a Quarantine Treatment for Commodities including Fresh Fruit, Cut
Flowers and Durables against Insects, other Arthropod Pests
and Nematodes. Guideline III Multiple Quarantine Treatments
Multiple quarantine treatments are sequential applications of two or more postharvest
treatments, which achieve quarantine security only when both are applied. For irradiation
this approach is relevant when a commodity is very susceptible to treatment injury.
Multiple treatments are usually proposed after research is completed for each single
treatment component and the efficacy data show that no single treatment will provide
quarantine security alone. The most tolerant developmental stage and the dose-mortality
relationship for each component must be experimentally determined. Multiple treatments
may have additive or synergistic effects on pest mortality. Dosimetry and response
of the commodity to the treatment must be determined for the irradiation treatment
and for the other treatment(s) eg heat; cold, modified atmosphere must be similarly
defined. Statistical confidence limits would be based on pest survival for the combined
treatments proposed. Treatment injury responses of the commodity, should be reported
for all treatments used to provide quarantine security. Chemical treatments are
unlikely to be combined with irradiation but where they are residue data will be
The following components are essential in the development of a multiple quarantine
i. Determine the highest risk developmental stage of the target pest that would
be encountered at the time of treatment for each of the components of the multiple
treatment. Internal organisms should be treated inside the commodity to determine
the most tolerant life stage. The most resistant stage must be determined for each
of the multiple treatments. When the most resistant stage to each component of the
treatment is the same, the preliminary tests to determine the treatment doses for
confirmatory testing may be performed as a single series of tests. If the most resistant
stages are different for each treatment component, a separate series of preliminary
tests may be required to determine the treatment doses for each component of the
confirmatory test. If previous research indicates that the first treatment(s) in
the sequence achieves the necessary quarantine security against certain developmental
stages, only the surviving stages need to be tested in subsequent treatments.
ii. Determine pest mortality for the range of treatment doses for each component
to predict the maximum number of survivors at the highest doses which can be tolerated
by the commodity. Based on results and calculations, propose a multiple treatment
schedule which will provide quarantine security. For irradiation, this is the highest
minimum of the potential commercial max/min ranges
iii. Confirm that the proposed multiple treatment schedule provides quarantine security
against the most resistant developmental stage of the target pest under actual or
simulated commercial conditions. In most cases involving treatments that are effective
on different developmental stages of the pest, separate confirmatory tests on each
developmental stage may be required to ensure that both stages are killed to provide
quarantine security. The sequence of treatments used in the confirmatory tests will
be the sequence approved for commercial use. Determine pest mortality to treatment
variables for each treatment component to predict maximum number of survivors for
each treatment. Based on results and calculations, propose a multiple treatment
schedule which will provide quarantine security.
It is essential that post-harvest physiology studies be done in conjunction with
pest disinfestation testing to ensure that treatments do not result in unacceptable
levels of injury to the commodity. These studies should include the production history
of the commodity as this can affect its response to irradiation.
The commodity should be subjected to a range of doses, if necessary using different
max/min dose geometry within the irradiator, temperatures, and modified atmospheres.
Electron beam irradiation response should be compared experimentally with gamma-
or x-radiation if it is intended to use that method but previous research had been
done with the other methods. Doses should be extended to a level where injury occurs
to identify the threshold. This would then become the upper limit permitted for
the max-min ratio.
Following are parameters, some or all of which could be used to assess possible
injurious effects in the product as a result of irradiation:
colour development or changes
softness of fruit or flower tissue
pH of fruit juice
Brix (total solids) of fruit as a measure of maturity
Ascorbic acid content of fruit
ethylene production patterns with time
CO2 production patterns with time
visible injuries - appearance
citric acid content of fruit
eating quality of fruit.
appearance of cut flowers
Data on these parameters should be collected using sound experimental designs and
should be analysed statistically. It should be done a representative range of production
areas and repeated over more than one season - ideally 3, taking the form of comparisons
with unirradiated fruit otherwise held identically.
Systems Approaches and Good Agronomic Practices
A Systems Approach to quarantine security is the integration of cultivation, preharvest
integrated pest management, harvest, postharvest treatment, packaging, storage,
handling, inspection, certification, and distribution practices for a host commodity
that, collectively, preclude establishment of a pest in an importing country. The
objective of using a systems approach is to prevent a mating pair or a fecund female
pest from entering the importing country in a shipment of the host commodity. To
establish a systems approach, it is necessary 1) to determine what combination of
practices reduces pest infestation risk to a level that will meet the above objective,
and 2) to determine, and be able to predict, maximum infestation levels of the pest
in a shipment of the commodity when it arrives in the importing country. Consistent
and documented usage of a standardised set of practices is important to success
and acceptance of a systems approach by the importing country. Efficacy of a systems
approach should be demonstrated experimentally for one quarantine pest in one commodity
at a time. In practice, a system may be set up to manage several pest species at
once in a commodity. Systems approaches may be used instead of stand-alone postharvest
commodity treatments or pest-free areas (described elsewhere in this protocol).
Systems may consist in part of purposeful disinfestation measures, such as irradiation
as well as routine operational procedures.
Good agronomic practices which minimise pest incidence are an important component
of any disinfestation program but they are especially important with irradiation
where mortality of pests will be slow. They may be linked to a systems approach.
If high levels of infestation are present in a commodity, live pests will be intercepted
at a post-treatment inspection and this will lead to concerns over whether a treatment
has been applied correctly. Although tests for irradiation of pests may be available,
such as the phenoloxidase test for fruit fly larvae, it is generally more practicable
to produce commodities with pest incidence below the level of detection. These production
practices can also assist in minimisation of irradiation injury to commodities such
as that which is linked to immaturity levels.
Non-host or Non-Infestable Concepts
Many commodities are not hosts of quarantine pests under field conditions. Some
commodities that are hosts are not infested by the pest at some stages of maturity.
Certain cultivars of known hosts may not be infested. If the non-host or non-infestable
condition can be clearly defined and monitored on a routine basis, the commodity
might be able to be harvested and shipped without a quarantine treatment. A host
is defined as a commodity, which is infested under normal field conditions (including
greenhouse conditions) which an organism can use to successfully complete its life
cycle. For the purpose of this document, non-host refers to a plant species that
the pest does not infest under normal field conditions or that the pest infests
but fails to complete its life cycle. The non-infestable concept refers to either
a cultivar of a known host or a stage of maturation of a host that the pest does
not infest. This is particularly useful where a host may have multiple quarantine
An evaluation of the literature, pest interceptions, and other evidence can usually
determine if a specific commodity is a host for the pest of concern. Table 1 identifies
the scientific parameters used in the Pest Risk Assessment to determine the host
If the commodity is determined to be a host, then some type of risk mitigation will
be required. An evaluation of the literature, pest interceptions, and other evidence
can usually determine this, or research might be used to identify a condition under
which the commodity is non-infestable. No mitigation or research is required if
the assessment determines that the commodity is not a host. It might not be possible
to determine whether a commodity is a host because evidence is lacking or questionable.
Regulatory authorities in the importing country would then consider the commodity
to be a host until additional information became available. The following research
procedures can help in determining host status when it is questionable. Tests of
this nature would only be initiated on pest/commodity combinations where doubt as
to host status existed:
Perform laboratory cage tests under optimum pest conditions. If cage tests result
in successful infestation defined as development through more than one generation,
field confirmation using the growing commodity should be done for a field pest.
Ensure that there are adequate numbers of pests, fruits, and replicates to provide
meaningful statistical results. Puncture (damage) some commodities to mimic normal
field injury. Commodities from different growing areas, cultivars, seasons or times
of the year may need to be tested. The fruit commodity should generally be of market
quality and this should be defined. Determining the factors conferring non-infestability
and the level of those factors is desirable.
A commodity cannot be considered non-infestable if infestability is demonstrated
in the field. However degree of infestability may be considered as a component of
a Systems Approach
A pest-free period is a time of the year during which a commodity can be exported
with minimal risk of infestation from an area in which a pest of regulatory concern
is found. The reproductive stage of the pest is not present during this period.
The pest-free period is applicable to species of pests that have no overlapping
generations during the season in which the commodity is grown and harvested. The
development time of a generation of the pest during the season in which the commodity
is harvested or the daily flight activity must be predictable. An effective method
of detecting the pest must be available. Detection of the reproductive stage of
the pest ends the pest-free period. Field monitoring may be an integral part of
The SPS Agreement formulated under the auspices of the World Trade Organisation
provides overall guidance for negotiation of market entry of commodities subject
to phytosanitary quarantine constraints. The format of a proposal for assessment
of a disinfestation treatment depends on the recipient country and should be prepared
on the advice of that country. It should be supported by full records of irradiation
treatments including timings, dosimetry results to an approved Standard and any
other relevant parameters. If possible a submission should be supported by skilled
technical advocates to ensure that there are no misunderstandings. It may also be
advantageous to enlist the assistance of importers and retailers in the recipient
country to counter the effects of producer lobbyists seeking to minimise competition.
Because mortality from irradiation often occurs late in the life cycle of a pest
when it is treated at low doses, any proposed treatment should be supported by "Quality
Control" or "Pest Management" programs which ensure that any pest infestations are
below the level of detection at any inspection at the time the disinfestation treatment
is applied. This is usually feasible because for many pests domestic markets will
not normally tolerate infested produce. An additional supporting facet would be
a means of determining whether the pest had been irradiated should it be detected
at pre- or post-entry inspection e.g. the phenol oxidase test for fruit flies.
The following tables of data should be included with a submission:
Development times for stages of the pest in culture medium used for naked insect
tests, range of times and/or mean or modal times ± S.E.
Development times for stages of the pest in each variety of the fruit or flower
proposed for export, range of times and/or mean or modal times ± S.E.
Treatment mortality or survivors of each stage of each pest species in each cultivar
at 5 evenly spaced doses resulting in 5 -100% survival. Additional doses or test
numbers at doses near 100% if appropriate.
Dose-response regression analyses on each stage of each pest species in each cultivar.
These should include representative appropriately transformed mortalities with 95%
fiducial limits, regression line parameters, parallelism-test results and if applicable,
comparisons of regression lines. They should meet all of the assumptions intrinsic
to the analysis model.
Alternatively, an ANOVA of response data at one or more doses comparing responses
of stages, with Least Significant Difference values could be given.
The size range of fruit should be given (size or weight) for any in fruit tests.
Results of tests to predict the dose needed for the required quarantine security
e.g. 99.5%, 99.99% or 99.9968% on the most tolerant stage in the cultivar in which
it is most tolerant (or highest risk stage).
Results of large-scale trials. Replicate number; Date treated; Fruit size range;
Stage of pest; Proportion present; Number of control fruit; Number of treated fruit;
Number of pupae from controls; Number of pupae from treated; Number of adults from
controls; Number of adults from treated; Number of adults from controls; Estimated
mortality of treated individuals.
Results of treatment injury testing giving the cultivar, maturity, ripeness and
where the commodity was grown.
Dosimetry data for all treatments and initial calibration of the irradiation source
and treatment geometry in accordance with an accepted international standard. Include
source, target dose, dose rate, max/min dose, max/min ratio, mean dose, distribution
of dose, temperature at treatment, RH of atmosphere, medium (in fruit, packing material,
naked insects), Absorber density, atmosphere (nitrogen, if ambient whether ventilated,
elevated or depressed levels of oxygen, nitrogen, carbon dioxide or other gases
present as atmospheric modifiers.
Documentation of source characteristics including strength, geometry and rate of