Modified Atmosphere Storage May Reduce Efficacy of Irradiation Phytosanitary Treatments

Ionizing irradiation is a phytosanitary treatment that is increasing in application. The effect of low-oxygen, modified atmosphere storage on irradiation efficacy has not been addressed until recently. Hypoxia for 18 hours before irradiation until a couple of hours after irradiation reduced efficacy to varying degrees as measured by adult development or reproduction for four insects studied. It is recommended that irradiation phytosanitary treatments not be approved for commodities stored under hypoxic conditions until adequate research determines the effect of the specific modified atmosphere on efficacy and provides proper solutions on a case by case basis. INTRODUCTION Ionizing irradiation is used as a phytosanitary treatment in the United States of America and Australia with widespread potential for further use throughout the world (Hallman, 2001). Storing and shipping agricultural commodities under hypoxic conditions is increasingly studied and practiced because it conserves quality and prolongs shelf life (Calderon and Barkai-Golan, 1990). It has been known for decades that hypoxia reduces the detrimental biological effects of irradiation because fewer oxidative radicals are formed under hypoxia than ambient air (Pizzarello and Witcofski, 1967). This knowledge is used to produce insects for sterile release programs that are still sterile while suffering fewer debilitative effects caused by radiation (Fisher, 1997). Sometimes the dose must be increased to ensure that insects irradiated under hypoxia are sterile. The effect of hypoxia on irradiation phytosanitary treatment efficacy has not been studied until recently. An estimated 17% increase in the ability of apple maggot, Rhagoletis pomonella, third instars to emerge as adults occurred when the larvae were held for 20 h before irradiation in a largely nitrogen atmosphere (Hallman, 2004b). When fifth instar oriental fruit moths, Grapholita molesta, were held in a near 100% nitrogen atmosphere for 20 h prior to irradiation with 200 Gy, 5.3% of the larvae developed to the adult stage (Hallman, 2004a), while none irradiated with 200 Gy in air developed to the adult stage. Reproduction of plum curculio, Conotrachelus nenuphar, increased 20 fold when adults were placed in nitrogen atmospheres 20 hours before irradiation versus adults irradiated in air (Hallman, 2005). The European corn borer, Ostrinia nubilalis, is a quarantine pest of agricultural products grown in North America east of the Rocky Mountains for shipment to the US west coast, British Columbia and many countries that do not have the pest in Latin America, Africa, Asia, and Pacific islands. For example, corn, broom corn, sorghum, sudangrass, green beans, bell peppers, and several flowers cannot be shipped to California unless they have been properly inspected or treated. Ionizing irradiation is being researched as a possible phytosanitary treatment against European corn borer (ECB). Because some of the products might be shipped under hypoxic conditions, the effect of hypoxia on irradiation efficacy needs to be studied. Proc. IX Intl. Contr. Atmos. Res. Conf.