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A Phytosanitary Solution

By: , Posted on: May 23, 2017

Cutting-edge research underway at the US Department of Agriculture Agricultural Research Service aims to advance irradiation on the world stage as a means of reducing insect pests present in fresh produce.

Being able to control the presence of insect pests in agricultural products is essential if growers are to export foodstuffs internationally without facilitating the movement of these pests across borders. Although postharvest insect control can be achieved through fumigation, this is not a fail-safe solution; for example, the fumigant methyl bromide is considered an ozone depleting chemical and, if used inappropriately, is toxic to humans. One alternative that is growing in popularity is phytosanitary irradiation, which employs electron beam, gamma ray and X-ray radiation to either kill or sterilise insect pests commonly found in fresh fruits and vegetables – a method that can prevent their global spread through trade.


At the US Department of Agriculture Agricultural Research Service (USDA-ARS) in Hawaii, Dr Peter A Follett and his colleagues are working to advance phytosanitary irradiation. Phytosanitary irradiation has been used in Hawaii since the 1990s as a means to prevent the invasive insect pests found in the state from reaching the US mainland, and it is often the simplest, fastest and most cost-effective approach. To date, its safety and benefits have been confirmed by organisations including the American Medical Association, Mayo Clinic, US Centers for Disease Control and Prevention, Food and Agriculture Organization of the UN (FAO), Scientific Committee of the European Union and World Health Organization. Follett’s first project with the USDA was the development of an irradiation quarantine treatment against mango seed weevil, and the export protocols that emerged from this research were so successful that they have since been employed in Hawaii, India and Pakistan. Following on from this, Follett turned his attention to the expansion of Hawaii’s first commercial X-ray irradiation facility, which was opened in 2000. His aim has been to create new treatments against quarantine pests that are capable of meeting regulatory requirements. “This collaboration turned out to be a great researcher-industry regulator partnership and, over the past 15 years, we have developed effective radiation

doses to control more than 20 key insect pests on two dozen fresh fruits and vegetables for export,” asserts Follett. Notable outputs to have emerged from this collaborative partnership include novel irradiation treatments for sweet potato and mango; a first-ever treatment for scale insects and hitchhiker ants; and the modification of existing treatments for bananas, papayas and several other fruits commonly produced in Hawaii for exportation.


One of Follett’s most significant successes to date has been his work on the establishment of generic treatments, which can be employed against a broad group of pests and for a wide range of commodities without adverse effects. Until recently, quarantine treatments were developed for one specific pest and commodity at a time – an R&D approach that was both lengthy and costly. Follett’s studies on radiation

tolerance in oriental fruit fly, Mediterranean fruit fly and melon fly, however, paved the way for the approval of a generic radiation dose of 150 gray (Gy) for the quarantine treatment of tephritid fruit flies (the most important group of quarantine pests worldwide), and of 400 Gy for all other insects except pupae and adult Lepidoptera (moths and butterflies). “This means that if a pest risk assessment demonstrates that no pupae or adult Lepidoptera are associated with a commodity, export approval can be forthcoming with no further research,” Follett explains. The US, Australia and International Plant

Protection Convention have already approved these generic doses, and the Codex Alimentarius Commission and FAO have also published guidelines relevant to their use. Follett is confident that the availability of these prescribed amounts will contribute to their wider acceptance and use on an international level: “Generic dose treatments make irradiation an attractive option compared with

other quarantine treatments because, in most cases, export protocols for new pests can be developed immediately without further research on efficacy,” he elucidates. “Also, if a new pest becomes a quarantine concern, trade will not be interrupted because the generic treatments are already approved and available.” At present, Follett and his collaborators are working to advance technology in this

area; current research activities include the development of specific doses for the quarantine Lepidoptera unaffected by generic dose treatments, and the establishment of generic doses below 400 Gy for economically important groups of quarantine arthropods other than fruit flies.


In addition to their generic dose research, Follett and his collaborators are furthering phytosanitary irradiation from several different angles. The team is seeking to reduce dose levels and, consequently, required treatment times for specific pests and commodities. The researchers also aim to improve commodity tolerance and extend shelf-life; contribute to the design of small-scale in-line cabinet X-ray machines; develop irradiation combination treatments involving plant essential oils; and advance modified atmosphere packaging (MAP) beyond current limitations. At present, regulators worry that MAP’s low-oxygen environment can increase insect radiation tolerance, and thus may compromise insect quarantine treatments.

In terms of future research, Follett is keen to explore a number of avenues. One is overcoming the 1 kilogray limit – a restriction imposed by the US Food and Drug Administration back in 1986. “The limit is a hindrance to application of the 400 Gy (0.4 kGy) generic dose owing to the high-dose uniformity ratio, which can reach 3:1 during treatment at high-energy, multi-purpose irradiation facilities,” Follett explains. “In a perfect world, the limit would be raised or eliminated to allow for more efficient commercial treatment, but changing the rule is a complicated and lengthy regulatory process. Alternatively, lowering the generic dose for insects would also solve the problem.

Another challenge that Follett aims to overcome relates to the appropriate labelling of foodstuffs that have been treated using irradiation. In the US, irradiated fresh food products must be labelled as such, despite the fact that no similar restrictions are applied to products that have undergone any other insect disinfestation processes. “Labelling can be an impediment to the marketing of irradiated fresh produce – retailers can be reluctant to carry irradiated fruits and vegetables because the label implies a warning,” Follett states. “If labelling remains a requirement for irradiated fresh commodities, more flexible and accurate labelling options might improve marketability and acceptance.

In the meantime, Follett and his team will continue to conduct cutting-edge research with the ultimate aim of supporting the universal acceptance of phytosanitary irradiation. By working to advance the available treatments and promote their benefits both within the US and further afield, their work is already beginning to pay dividends.

About the book

Irradiation for Quality Improvement, Microbial Safety and Phytosanitation of Fresh Produce

Irradiation for Quality Improvement, Microbial Safety and Phytosanitation of Fresh Produce presents the last six and a half decades of scientific information on the topic. This book emphasizes proven advantages of ionizing irradiation over the commonly used postharvest treatments for improving postharvest life of fresh fruits and vegetables to enhance their microbial safety. This reference is intended for a wide range of scientists, researchers, and students in the fields of plant diseases and postharvest diseases of fruits and vegetables. It is a means for disease control to promote food safety and quality for the food industry and can be used in food safety and agriculture courses.

Visit to and use discount code STC317 at checkout and save up to 30% on your very own copy!

About the author

peter follettDr. Peter Follett is a Research Entomologist with the USDA Agricultural Research Service (ARS) in Hilo, Hawaii, where he coordinates research efforts to develop new or improved postharvest treatments to control quarantine pests that restrict the export of tropical fruits and vegetables. He has authored or co-authored 180 scientific publications and is recognized internationally as an expert in the areas of postharvest entomology and commodity quarantine treatment. His research on the radiobiology of more than three dozen insect pests was used to develop first-ever generic irradiation treatments, which are now used worldwide and have helped expand international trade in tropical fruits and vegetables. Dr. Follett received the Entomological Society of America (ESA) Distinguished Achievement Award in Horticultural Entomology, the USDA Secretary’s Group Honor Award for Excellence, and the Federal Laboratory Consortium (FLC) Award for Excellence in Technology Transfer for his accomplishments in phytosanitary irradiation research and commodity quarantine treatment development.

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