Influence of Modified Atmosphere Packaging on Radiation Tolerance in the Phytosanitary Pest Melon Fly (Diptera: Tephritidae)

Abstract

Modified atmosphere packaging (MAP) produces a low-oxygen (O2) environment that can increase produce shelf life by decreasing product respiration and growth of pathogens. However, low O2 is known to increase insect tolerance to irradiation, and the use of MAP with products treated by irradiation before export to control quarantine pests may inadvertently compromise treatment efficacy. Melon fly, Bactrocera cucurbitae Coquillet (Diptera: Tephritidae), is an important economic and quarantine pest of tropical fruits and vegetables, and one of the most radiation-tolerant tephritid fruit flies known. The effect of low O2 generated by MAP on the radiation tolerance of B. cucurbitae was examined. Third-instar larval B. cucurbitae were inoculated into ripe papayas and treated by 1) MAP + irradiation, 2) irradiation alone, 3) MAP alone, or (4) no MAP and no irradiation, and held for adult emergence. Three types of commercially available MAP products were tested that produced O2 concentrations between 1 and 15%, and a sublethal radiation dose (50 Gy) was used to allow comparisons between treatments. Ziploc storage bags (1-4% O2) increased survivorship to adult from 14 to 25%, whereas Xtend PP61 bags (3-8% O2) and Xtend PP53 bags (11-15% O2) did not enhance survivorship to the adult stage in B. cucurbitae irradiated at 50 Gy. Radiation doses approved by the United States Department of Agriculture and the International Plant Protection Commission for B. cucurbitae and Ceratitis capitata (Wiedemann) (Mediterranean fruit fly) are 150 and 100 Gy, respectively. In large-scale tests, 9,000 B. cucurbitae and 3,800 C. capitata larvae infesting papayas in Ziploc bags were irradiated at 150 and 100 Gy, respectively, with no survivors to the adult stage. MAP can increase insect survivorship during irradiation treatment at certain doses and O2 concentrations, but should not compromise the efficacy of the 150-Gy generic radiation treatment for tephritid fruit flies or the 100-Gy radiation treatment for C. capitata.

Detrimental effects of electron beam irradiation on the cowpea bruchid Callosobruchus maculatus

“…Generic radiation doses have to be carefully established because different insect species and different developmental stages often exhibit differing radiosensitivity . To achieve high confidence, environmental factors that may affect irradiation efficacy, such as temperature, host and oxygen content, should be taken into consideration. It is also critically important to gain a better understanding of how alterations in ambient conditions owing to modified atmosphere packaging (MAP) would affect the radiosensitivity of the different life cycle stages.…”

Phytosanitary Irradiation

“…Therefore, plant protection organizations have prohibited the use of PI on commodities stored in hypoxic atmospheres if the research supporting its use under hypoxic conditions has not been done [27,33]. Although some research has shown that this is not a problem for tephritid fruit flies [34,35] definitive research is needed to put to rest this issue for this important group of quarantine pests. Additionally, some research was done using larvae reared on diet and inserted into holes bored to the centre of fruits [35], which presents a series of untested assumptions concerning results of these studies.…”

“…Although some research has shown that this is not a problem for tephritid fruit flies [34,35] definitive research is needed to put to rest this issue for this important group of quarantine pests. Additionally, some research was done using larvae reared on diet and inserted into holes bored to the centre of fruits [35], which presents a series of untested assumptions concerning results of these studies. Regardless of the final conclusion for fruit flies, irradiation in hypoxic atmospheres seems more of a concern for most other quarantine pests, which seem to respond to hypoxia to a greater extent than fruit flies [36].…”

Critical PO2 as a diagnostic biomarker for the effects of low‐oxygen modified and controlled atmospheres on phytosanitary irradiation treatments in the cabbage looper Trichoplusia ni (Hübner)

“…There was a trend towards greater numbers of larvae irradiated in the lowest hypoxic bags (1–4 kPa O 2 ) surviving to adulthood, but none of the larvae irradiated in modified atmosphere packaging bags had statistically significantly greater survival than larvae irradiated in normoxia when treated at 50 Gy. At the 150 Gy generic dose for fruit fly larvae, no larvae survived to adulthood after irradiation in any of the modified atmosphere packaging treatments . Similarly, Follet et al .…”

“…Phytosanitary irradiation removes the risk of pest incursions and reduces post‐harvest losses, without damaging or changing the quality of most commodities . Phytosanitary irradiation is also an increasingly attractive treatment for growers and distributors because commodities can be irradiated after packing at the point of origin, or even after shipping at the point of arrival . Some producers would like to combine phytosanitary irradiation treatments with controlled or modified atmosphere packaging that preserves the quality and increases the shelf life of fresh commodities.…”