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The mango pulp weevil

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Under a stereomicroscope, a DOST-PNRI researcher separates male and female MPWs for mating and fecundity study

PH nuclear agency sets international standard for mango pest treatment

As a result of a breakthrough study, the standard for the quarantine treatment of a persistent mango pest is finally set by the Department of Science and Technology-Philippine Nuclear Research Institute (DOST-PNRI). Said development now gives Philippine mangoes a better chance at the global market and a push for the local mango industry as well.

Said treatment involves irradiating mangoes at a certain dose that will make the Sternochetus frigidus (Fabr.), or mango pulp weevil (MPW), sterile.

“This ensures that the weevil will no longer be able to reproduce,” says Glenda Obra of PNRI’s Agriculture Research Section and the leader of the research “Establishment of radiation dose for quarantine treatment of mango pulp weevil (MPW), Sternochetus frigidus Fabr in Philippine Mango.” The study was conducted in collaboration with the Department of Agriculture, Regional Field Unit 4B.

As the PNRI study found, irradiating the pest using 165 Gy dose sterilizes it, and prevents the production of the next generation of MPW. This breakthrough opened US markets for Philippine mango exports.

“Other countries use the generic dose of 400 Gy, but at this dose, the quality of our Philippine Carabao or Philippine Super Mango will be affected,” explains Obra. “Our mango variety is more sensitive because of its thin peel.”

S. frigidus, or bukbok ng mangga in Tagalog, is most destructive during the larval stage as it feeds and develops on the sweet mango pulp.   According to literature, S. frigidus was probably introduced in 1987 from Borneo into the southern part of Palawan. Since then, the government put the island group under quarantine to prevent the spread of the pest. This move dropped the overall mango production in Palawan by 30%.

As the pests cannot be easily seen through visual inspection, they can only be controlled through postharvest treatment. The usual procedure is fumigation or cold heat, but this has not been successful when used to treat S. mangiferae, a close relative of the S. frigidus.

The only viable alternative to disinfest S. frigidus, is through irradiation which, according to WHO, does not leave residues and does not make the food harmful to human health.

In 2014, the USDA-Animal Plant Health Inspection Service included the PNRI-set irradiation treatment in the USDA’s Plant Protection Quarantine Treatment Manual. “The dose can also be used to control fruit fly. This provided the scientific basis that eventually led to the USDA Final Rule,” adds Obra.

Eventually, the project team submitted its proposed irradiation treatment of S. frigidus to the FAO-International Plant Protection Convention in 2017 through the Philippine Bureau of Plant Industry’s National Plant Protection Office.

After a series of annual reviews, rigorous evaluations by the Technical Panel of Phytosanitary Treatment, and two public consultations held through the IPPC Online Comment System, the Commission on Phytosanitary Measures (CPM) finally recommended and publicly endorsed the adoption and inclusion of the treatment in the International Standard of Phytosanitary Measures 28 in April 2022.

The CPM endorsement put DOST-PNRI on the map as a first-mover in the country in establishing a global standard in disinfestation through irradiation. “It is the first time for the Philippines to have a phytosanitary treatment, specifically one involving irradiation, approved and adopted by the FAO-IPPC,” says Obra. (Framelia V. Anonas, DOST-PNRI)

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DOST-PNRI researchers dissect mangoes infested by the Mango Pulp Weevil at the Institute’s MPW Holding Laboratory