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Irradiation as a Quarantine Treatment: Research Protocols (Guideline I)

‚ÄčIrradiation as a Quarantine Treatment for Commodities including Fresh Fruit, Cut Flowers and Durables against Insects, other Arthropod Pests and Nematodes. Related methodologies: Research and Development of a Single Component Quarantine Treatment or Multiple Components Applied Concurrently (Guideline II), Multiple Quarantine Treatments (Guideline III), Supporting services and facilities (Guideline IV) and Check list (Guideline V).
Irradiation for quarantine (phytosanitary) purposes, must have a scientifically demonstrated level of efficacy whether it is used as a single treatment, part of a multiple treatment, or combined with other pest mitigation measures as a component of a systems approach. The research necessary to demonstrate the efficacy of any plant protection quarantine (PPQ) treatment begins with graded dose efficacy tests. These provide results that can be analysed statistically to establish the dose required to achieve a treatment efficacy that will give the desired level of quarantine security. Quarantine treatments with irradiation mostly utilise gamma rays from commercially available radioactive sources such as 60 cobalt, 137 caesium or X-rays (bremsstrahlung) generated electrically by an electron beam striking an intervening high density material eg lead, to deliver ionising radiation. An electron beam itself can also be used deliver an ionising radiation treatment. However, electron penetration is much poorer than that of gamma rays or X-rays and can only be used to treat produce loads of no more than 5-10 cm in depth, such as rotating single layers of fruits, a thin stream of grain or shallow boxes of cut flowers on a conveyor. Any of these radiation sources can be used experimentally provided that the absorbed dose range can be controlled and measured. Irradiation will be used most often as a single treatment although a combined treatment such as with cold storage or heat may be advantageous.
Doses of irradiation required to kill every pest present, in less than a day, are usually too high for most produce to tolerate without unacceptable effects on commercial quality. However, much lower doses (20-500 Gy) can cause total mortality after some time or result in total sterility, which is equivalent to mortality in preventing the next generation. In practice, the goal of an irradiation quarantine treatment is usually to cause mortality of immature stages before development to the adult or, where the stage present is an adult, to prevent further reproduction.
The research procedure involves, firstly, accurate determination of the pest species of quarantine significance for the host commodity, found in the geographic location from which exports are intended. The taxonomic identity of the pest species and of the commodity must be agreed upon with the proper authorities of the importing country before developing research plans for disinfestation treatments. There must also be concurrence on the exclusion of any species from host or pest testing. Some pests vary with respect to hosts or may occur as recognisable geographic races and are liable to be redesignated by taxonomic subdivision eg. oriental fruit fly. Voucher specimens from the test population should be lodged in a secure tenure museum against the possibility of future dispute.

As with any quarantine treatment, the life stage of the pest representing the highest risk and occurring on or in the commodity at export, must be determined, and research concentrated on that stage. Usually this is the life stage most tolerant of the treatment. For irradiation, the most