Phytosanitary Irradiation Treatment Research Articles

Effects of phytosanitary irradiation on the quality and postharvest storage performance of ‘Orri’ mandarins

‘Orri’ is the main mandarin (Citrus reticulata Blanco) cultivar grown in Israel and exported to global markets. As part of the export process, these fruits are exposed to quarantine treatments against the Mediterranean fruit fly Ceratitus capitate. In the current study, we examined the effects of phytosanitary ionizing irradiation treatments at doses of between 150 and 400 Gy on the quality and postharvest storage performance of ‘Orri’ mandarins. In 2021, we exposed ‘Orri’ mandarins to gamma irradiation doses of 150 and 400 Gy, and then stored the fruit for 3 or 6 weeks at 5 °C, followed by one additional week under shelf-life conditions at 22 °C. In 2022, we exposed ‘Orri’ mandarins to 150 Gy, which is the approved quarantine treatment against fruit flies, and then stored the fruit for 4 or 9 weeks at 5 °C, followed by one or two additional weeks under shelf-life conditions at 22 °C. The results indicate that the examined irradiation treatments do not affect the quality or postharvest storage performance of ‘Orri’ mandarins, as no significant differences were observed between the treated fruit and the untreated control fruit, in terms of weight loss, firmness, color, decay, peel damage, juice total soluble solids, acidity and vitamin C contents, ethanol accumulation or perceived flavor. We conclude that 'Orri’ mandarins are tolerant of postharvest phytosanitary irradiation treatments.

Phytosanitary irradiation treatment of the aerial root mealybug, Pseudococcus baliteus (Hemiptera: Pseudococcidae).

The aerial root mealybug, Pseudococcus baliteus Lit (Hemiptera: Pseudococcidae), is an important invasive and quarantine pest that poses a potential threat to fruits, vegetables, and ornamental plants. As a result, phytosanitary treatments are necessary to ensure the commodities of international trade are free from these pests. To determine the minimum absorbed dose required for phytosanitary irradiation (PI) application, irradiation dose-response and large-scale confirmatory tests were conducted. Eggs that were 2, 4, and 6 days old and late gravid females (containing 0-day-old eggs) of P. baliteus were X-ray irradiated with doses of 10, 20, 40, 60, 80, 100, and 120 Gray (Gy). The efficacy of preventing egg-hatching (mortality) was compared using two-way ANOVA, 95% confidence interval overlapping and lethal dose ratio test in probit analysis. The radiotolerance sequence of mealybugs egg was found to be 0 < 2 ≈ 4 < 6-day-old eggs, and their estimated LD99.9968 values with 95% confidence interval were 132.0 (118.9-149.5), 137.6 (125.2-153.7), 145.5 (134.5-159.1), and 157.4 (144.6-173.6) Gy, respectively. Subsequently, target doses of 135 and 145 Gy were used in the confirmatory gamma radiation treatments. No F1 generation neonates developed from a total of 47,316 late females irradiated at the measured dose of 107.7-182.5 Gy, resulting in the treatment efficiency of 99.9937% at the 95% confidence level. Therefore, the highest dose of 183 Gy measured in the confirmatory tests is recommended as the minimum absorbed dose in PI treatment of P. baliteus for establishing national and international standards.

Quarantine Disinfestation of Papaya Mealybug, Paracoccus marginatus (Hemiptera: Pseudococcidae) Using Gamma and X-rays Irradiation.

Paracoccus marginatus is a highly polyphagous invasive pest that poses a significant quarantine threat to tropical and subtropical countries. Infested commodities in international trade should undergo phytosanitary treatment, and irradiation is recommended as a viable alternative to replace methyl bromide fumigation. Dose-response tests were conducted on the 2-, 4-, and 6-day-old eggs and gravid females of P. marginatus using the X-ray radiation doses of 15-105 Gy with an interval of 15 Gy. Radiotolerance was compared using ANOVA, fiducial overlapping and lethal dose ratio (LDR) test, resulting in no significant difference among treatments, except for the overall mortality and LDR at LD90 (a dose causing 90% mortality at 95% confidence level). The estimated dose for LD99.9968 was 176.5-185.2 Gy, which was validated in the confirmatory tests. No nymphs emerged from a total of 60,386 gravid females exposed to a gamma radiation dose range of 146.8-185.0 Gy in the confirmatory tests. The largest dose in confirmatory tests should be the minimum threshold for phytosanitary treatment, consequently, a minimum dose of 185 Gy is recommended for the phytosanitary irradiation treatment of papaya mealybug-infested commodities, ensuring a treatment efficacy of ≥99.9950% at 95% confidence level.

Effects of phytosanitary irradiation treatment and refrigerated storage on the physicochemical properties of three pectin types isolated from mandarin pulp

The impact of fruit exposure to ionizing energy as phytosanitary treatment on pectin properties has received little attention, especially on that from the flesh of citrus fruit other than oranges. In this study, hot-water, chelating agent and alkali soluble pectins (HWSP, CASP and ASSP) were extracted from juiced segments of mandarins that were treated with γ-irradiation (0, 0.15, 0.4 and 1 kGy) and stored (3 wks at 6 °C + 1 wk at 20 °C). Irradiation increased the recovery of HWSP and CASP and decreased the molecular weight (MW), the degree of methyl esterification (DME) and the protein content of the pectins. Storage further enhanced the recovery and the reduction of DME and MW of all tested pectins. The sum of the contents of arabinose, galactose, mannose and xylose was always lower in pectin from stored fruit as compared to pectin from non-stored fruit, independent of irradiation. Irradiation influenced the viscosity of the tested pectins from non-stored fruit. It did not impact the viscosity of pectins from stored fruit, which had a lower viscosity than that of pectins from non-stored fruit. Irradiation increased the hysteresis of pectins, independent of storage. Overall, irradiation and storage impacted the physicochemical properties of the pectins, negatively affecting their functionality.

The applicability of species sensitivity distributions to the development of generic doses for phytosanitary irradiation

Ionizing radiation is used as a phytosanitary treatment to prevent the introduction of pests through trade. Generic doses are a valuable means to increase the number of pest-commodity combinations that can be treated using phytosanitary irradiation. Generic doses allow for the treatment of the entire taxa for which the dose has been approved, allowing for the treatment of untested species. As such, the approval of a generic dose requires substantial supporting data and careful consideration of the risks involved. We adopt the Species Sensitivity Distribution (SSD) framework, already in widespread use in the field of ecotoxicology and environmental risk assessment, to evaluate generic doses for phytosanitary irradiation treatments. Parametric SSDs for Curculionidae and Tephritidae were developed using existing data on efficacious phytosanitary irradiation treatments. The resulting SSDs provided estimates of the taxa coverage expected by the generic dose, along with the margin of uncertainty. The SSD analysis lends support to the existing 150 Gy generic dose for Tephritidae and a proposed 175 Gy generic dose for Curculionidae. The quantitative estimates of risk produced by the SSD approach can be a valuable tool for phytosanitary rule making, improving the process for generic dose development and approval.

Gamma and X-ray irradiation as a phytosanitary treatment against various stages of Planococcus lilacinus (Hemiptera: Pseudococcidae)

• Late-aged adult female of cacao mealybug is most tolerant to gamma and X-ray irradiation. • None F 1 generation 2nd instar nymphs emerged from 97,384 adult females irradiated at 126.1-163.0 Gy in confirmatory tests. • The treatment efficacy is not less than 99.9969% at the 95% confidence level. • A minimum of 163 Gy is suggested for phytosanitary irradiation treatment of cacao mealybug. The cacao mealybug, Planococcus lilacinus Cock, is an important quarantine pest. Infested commodity should be subject to appropriate phytosanitary treatment, while irradiation is recommended for the cacao mealybug. Radio-tolerance comparison tests were conducted on the crawler, nymphs, and adult females of P . lilacinus at the X-ray radiation doses of 40, 80, and 120 Gy, respectively. The results showed that irradiation had a strong effect on preventing of development and reproduction; the adult female stage was identified as the most tolerant. During the following dose-response tests, among young and late females X-ray-irradiation (20–100 Gy), the late females were most tolerant when preventing F 1 generation 2nd instars emergence was used as the evaluation criterion. Minimum absorbed dose and its 95% fiducial limits to provide probit 9 efficacy at 95% confidence level (100% mortality/inhibition in an estimated population of 93,616 individuals) were 131.5 Gy (122.5, 142.6 Gy) and 144.4 Gy (132.7, 159.4 Gy), estimating from the probit analysis on dose-mortality data of 1–30 and 1–10-day-old neonates laid by late females, respectively. In the large-scale confirmatory tests, a total of estimating 97,384 late females of P. lilacinus rearing on the pumpkins fruits were irradiated with gamma-ray at the target dose of 135 or 145 Gy (measured doses 126.1–163.0 Gy), which resulted in no F 1 generation 2nd nymphs developing during a 6-week post-treatment period. The treatment efficacy calculated is 99.9969% at the 95% confidence level. Therefore, a minimum absorbed dose of 163.0 Gy is recommended for phytosanitary treatment of P. lilacinus in infested commodity.

Effect of Phytosanitary Irradiation Treatment on the Storage Life of ‘Jiro’ Persimmons at 15 °C

Irradiation is becoming a more accepted phytosanitary market access treatment for some international horticultural trades. However, there is little information on the effects of phytosanitary irradiation treatment on persimmon fruit quality. ‘Jiro’ persimmon fruit were treated with an average of 769 Gray (Gy) at a commercial phytosanitary irradiation X-ray facility to examine the effect of this market access treatment on fruit quality during storage. After treatment, fruit were stored in air at 15 °C for up to three weeks. The results showed that, in general, there was no effect of irradiation treatment on fruit weight loss, calyx appearance, fruit firmness (objective and subjective), total soluble solids (TSS), titratable acidity (TA), internal appearance, and ethylene production rate. There were some treatment differences in fruit respiration rates and some aspects of fruit appearance and colour, where irradiated fruit had higher respiration rates and were slightly darker with higher levels of skin blemish, although these measured differences were not commercially significant. This study showed the promise of using low dose irradiation as a phytosanitary treatment for ‘Jiro’ persimmons, but more work is required to test other persimmon cultivars and other storage and marketing environments.

Radioprotective Effects on Late Third-Instar Bactrocera dorsalis (Diptera: Tephritidae) Larvae in Low-Oxygen Atmospheres.

Simple SummaryThe oriental fruit fly Bactrocera dorsalis Hendel is a highly invasive fruit fly that causes extensive damage to many fruits and vegetables. Irradiation treatment is an economically effective and promising treatment measure. However, treatment efficacy is affected by the presence of low oxygen, i.e., mangoes are treated in modified atmosphere package. In order to investigate the reduced (radioprotective) effects on insects and determine its critical O2 level, third-instar B. dorsalis larvae were irradiated by X-rays at the doses of 8 to 64 Gy with intervals of 8 Gy. The treatments were conducted under ambient air or low-oxygen atomospheres (0%, 2%, 4%, 6%, 8% O2 and nitrogen). No adult emergence from treatments at 64 Gy in pure nitrogen or 56 Gy under other atmospheres, resulted in significant difference in tolerance. The results from statistical analyses indicate that differences in tolerance to radiation were significant in 0% and 2% O2 but insignificant in 4%, 6%, and 8% O2 environments when compared with radiation in ambient air. Therefore, the critical threshold is an O2 level of ≥4% and <6%, but a maximum radiation dose of 14 Gy can compensate for the radioprotective effects when the oriental fruit fly is treated in low-oxygen atmospheres.Ionizing radiation creates free radicals, the effect of which is enhanced by the presence of oxygen; a low oxygen level produces radioprotective effects for insects compared with irradiation in ambient air. Modified (controlled) atmosphere packaging is used for maintaining quality and shelf-life extension; therefore, treatment efficacy may be affected, and there is a need to determine the critical O2 levels that may cause radioprotective effects. Late third-instar Bactrocera dorsalis (Hendel) larvae were irradiated in bags filled with ambient or low-oxygen air (0%, 2%, 4%, 6%, 8% O2) and were exposed to radiation doses of 8 to 64 Gy with intervals of 8 Gy. Efficacy was measured by the prevention of adult emergence. Dose–response data on mortality (failure of adult emergence) were analyzed via two-way ANOVA (analysis of variance), ANCOVA (analysis of covariance), and probit regression. The difference in radiotolerance was only significant in 0% O2 atmospheres through two-way ANOVA; therefore, the 95% confidence limits (CLs) of lethal dose ratios at LD99 were used to determine significant differences between treatments at different O2 levels. The differences in radiotolerance were significant in 0% and 2% O2 but insignificant in 4%, 6%, and 8% O2 environments when compared with radiation in ambient air. The critical threshold of radioprotective effects for late third-instar B. dorsalis larvae is an O2 level of ≥4% and <6%, but a maximum radiation dose of 14 Gy can compensate for this effect during phytosanitary irradiation treatment.

Phytosanitary irradiation: Does modified atmosphere packaging or controlled atmosphere storage creating a low oxygen environment threaten treatment efficacy?

Phytosanitary irradiation treatment is used to control insects in fresh commodities so that the commodities can be safely exported to pest-free areas. The goal of phytosanitary irradiation is to prevent reproduction. Modified atmosphere packaging (MAP) and controlled atmosphere (CA) storage creating a low oxygen environment are used to preserve the quality of fruits and vegetables. Low oxygen is known to be radioprotective in insects and other organisms. This raises the question of whether MAP or CA may reduce the efficacy of phytosanitary irradiation treatments. IPPC regulations prohibit the application of phytosanitary irradiation for fruits and vegetables under modified atmospheres. Studies used to support this restriction have typically used unrealistic conditions, particularly with the use of severe hypoxia or anoxia and short duration exposures after irradiation (≤2 h hold time under low oxygen). Results from these studies have been extrapolated to suggest phytosanitary irradiation may be compromised by MAP or CA. Although low oxygen radioprotection in insects has been demonstrated for various biological parameters such as adult emergence, flight ability, mating success, and fertility, to date no studies have shown that irradiation of insects at approved doses under modified atmospheres results in treatment failure, i.e., allows successful reproduction. Recent studies using commercially relevant conditions show that MAP may improve control due to the toxic effect of extended exposures to low O2 and high CO2 to insects. Regulatory restrictions on the use of MAP and CA during irradiation treatment should be reviewed and reconsidered. In the absence of data showing treatment failure due to modified atmospheres, current regulatory restrictions are not scientifically justified.

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).

Phytosanitary irradiation is a sustainable alternative to chemical fumigants for disinfesting fresh commodities from insect pests. However, irradiating insects in modified atmospheres with very low oxygen (<1 kPa O2 ) has repeatedly been shown to increase radioprotective response. Thus, there is a concern that modified atmosphere packaging could reduce the efficacy of phytosanitary irradiation. One hurdle slowing the widespread application of phytosanitary irradiation is a lack of knowledge about how moderate levels of hypoxia relevant to the modified atmosphere packaging of most fresh commodities (3-10 kPa O2 ) may affect phytosanitary irradiation treatments. Therefore, we hypothesize that critical PO2 (Pcrit ), the level of oxygen at which an insect's metabolism becomes impaired, can be used as a diagnostic biomarker to predict the induction of a radioprotective response. Using the cabbage looper Trichoplusia ni (Hübner), we show that there is a substantial increase in radiation resistance when larvae are irradiated in atmospheres more hypoxic than their Pcrit (3.3 kPa O2 ). These data are consistent with our hypothesis that Pcrit could be used as a diagnostic biomarker for what levels of hypoxia may induce radioprotective effects that could impact phytosanitary irradiation treatments. We propose that the relationship between Pcrit and radioprotective effects could allow us to build a framework for predicting the effects of low-oxygen atmospheres on the efficacy of phytosanitary irradiation. However, more widespread studies across pest species are still needed to test the generality of this idea.

Postharvest Irradiation Treatment for Quarantine Control of Western Flower Thrips (Thysanoptera: Thripidae).

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an important pest of fresh horticultural produce and as such is considered a biosecurity risk in many countries from which it is absent. Information is needed on the radiation tolerance of important surface pests of quarantine importance such as F. occidentalis so that phytosanitary irradiation treatments for exported fresh commodities can be lowered to below the 400 Gy generic treatment currently approved for most insects in the United States and Australia. Lowering the dose will help minimize any product quality problems, reduce costs, and shorten treatment time. In large-scale confirmatory trials conducted in two independent laboratories in Hawaii and Australia, a dose of 250 Gy (measured doses 222-279 Gy) applied to adult F. occidentalis on green beans resulted in no reproduction in 5,050 treated individuals. At 250 Gy, the effective dose is significantly below the 400 Gy generic dose, demonstrating that irradiation at this lowered level is an effective method for the disinfestation of F. occidentalis from fresh horticultural produce.

Effects of X-ray irradiation on different stages of Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae) and DNA damage

The corn stalk borer, Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae) is an important corn pest in the Mediterranean countries. In this study, we investigated the influence of X-ray irradiation on different developmental stages, reproduction and DNA damage to the insect. Eggs (0–24h old), larvae (5th instar), pupae (5 days after pupation) and adults (24h after emergence) were irradiated with X-ray irradiation at target doses of 0 (control), 50, 100, 150 and 200Gy. Eggs irradiated at all doses did not hatch. When 5th instar were irradiated pupation and adult emergence significantly decreased. Fecundity of adults from irradiated pupae was inhibited and no eggs were laid. Moreover, adult longevity decreased after irradiation compared to control. Larvae, pupae, and adults of S. nonagrioides were studied using the single-cell gel electrophoresis (DNA comet) directly after irradiation. X-ray irradiated larvae, pupae, and adults showed typical DNA fragmentation in a dose-dependent manner compared with cells from non-irradiated groups. The amount of DNA damage increased as doses increased and possibly could be used to estimate dose applied in commercial phytosanitary irradiation treatments. Furthermore, irradiation would be an effective phytosanitary treatment for shipped commodities at risk infestation with S. nonagrioides.

Gamma radiation as a phytosanitary treatment against larvae and pupae of Bactrocera dorsalis (Diptera: Tephritidae) in guava fruits

A low-dose gamma radiation phytosanitary treatment against the oriental fruit fly, Bactrocera dorsalis Hendel, was developed for guava fruits. The measure for efficacy of the treatment is preventing adult emergence from late third instars that were reared in the fruit of guava, Psidium guajava L. The dose–response tests with 1-, 2-, 3-, 7-d-old larvae in guava were initiated to determine the most tolerant stages, the late-aged third instars. No adult emerged from a total of 100,684 late-aged third instars irradiated at the dose of 97–116 Gy, resulting in an efficacy of 99.9970% at the 95% confidence level. The minimum dose for 100% preventing adult emergence from 2-, 5-, 7-d-old pupae (1800 pupae in each dose) reared in artificial diets was 100, 500, and 1750 Gy, respectively. Quality determinations on ‘Taiwan’ guavas were conducted at 1, 3 and 7 days after gamma radiation at doses of 200, 400, 600, 800, 1,200, 2000 and 6000 Gy. The guavas could tolerate radiation dose up to 600–800 Gy as there were no significant changes in organoleptic characteristics (≤800 Gy), the chemical and nutritional contents (sugar, sucrose, total sugar, titratable acid, vitamin C, and soluble solid) (≤600 Gy). Therefore, a dose of 116 Gy, which give the disinfestations efficacy of 99.9968% for the late-aged larvae in guavas and 100% mortality of 2-d-old pupae, is suggested as the minimum absorbed dose for phytosanitary irradiation treatment of B. dorsalis in fruits.

Phytosanitary Irradiation.

Phytosanitary treatments disinfest traded commodities of potential quarantine pests. Phytosanitary irradiation (PI) treatments use ionizing radiation to accomplish this, and, since their international commercial debut in 2004, the use of this technology has increased by ~10% annually. Generic PI treatments (one dose is used for a group of pests and/or commodities, although not all have been tested for efficacy) are used in virtually all commercial PI treatments, and new generic PI doses are proposed, such as 300 Gy, for all insects except pupae and adult Lepidoptera (moths). Fresh fruits and vegetables tolerate PI better than any other broadly used treatment. Advances that would help facilitate the use of PI include streamlining the approval process, making the technology more accessible to potential users, lowering doses and broadening their coverage, and solving potential issues related to factors that might affect efficacy.

A comparative study on the effects of electron beam irradiation on imidacloprid-resistant and -susceptible Aphis gossypii (Hemiptera: Aphididae)

Abstract The melon and cotton aphid, Aphis gossypii, is a polyphagous insect pest. This study compared the development, reproduction, DNA damage, recovery, and gene expression in imidacloprid-resistant (IMI-R) and -susceptible (S) strains of A. gossypii by electron beam irradiation. When 1st instar nymphs were irradiated with 100 Gy, the fecundity (nymphs of F1 generation) of the resultant adults were completely inhibited. When adults were irradiated with 200 Gy, the number of total 1st instar nymphs produced per adult was 3.0±1.7 and 1.9±1.4 in the S and IMI-R strains, respectively, but adult development was completely suppressed. However, electron beam irradiation did not affect adult longevity in either the S or IMI-R strain. There was no statistically significant difference between the effect of irradiation on the S and IMI-R strains. Therefore, electron beam irradiation at 200 Gy could be used as a phytosanitary irradiation treatment for both S and IMI-R strains of A. gossypii. The DNA damage caused by electron beam irradiation was evaluated by an alkaline comet assay. Exposure to an electron beam (50 Gy) induced DNA damage that was repaired to a similar level as the untreated control group (0 Gy) over time. However, at more than 100 Gy, the DNA damage was not completely repaired. The expression of P450, HSP70, cuticle protein, and elongation factor genes were higher in the IMI-R strain than in the S strain.

Improving phytosanitary irradiation treatment of mangoes using Monte Carlo simulation

Mango is a popular tropical fruit, comprising approximately half of all tropical fruits produced worldwide. Phytosanitary irradiation is a promising treatment as an alternative to fumigation. Most of the irradiation, however, is done in pallet loads, resulting in non-uniform dose distribution in fruits. Therefore, accurate dose calculation is needed to ensure proper process control to minimize quality changes. Our objective was to evaluate phytosanitary irradiation treatment for mangoes in pallet loads. Mango’s 3D geometry, ellipsoid shape, based on Computed Tomography data, was used to simulate dose distributions in mangoes using radiation transport code (MCNP5). To calculate average doses at different depths, mango flesh was divided into 20 segments from the surface to the seed. Mango was divided into 0.05-cm vertical sections to calculate doses along the major axis. Radiation energy was 1.25MeV from a Cobalt-60 source. For one-directional irradiation, doses from the surface to the mango seed had a build-up region at the outermost region (up to 0.13cm) with only 78% of the average dose. An average dose at the outermost segment up to the center of the fruit (0.37kGy) was significantly less than 0.56kGy at the middle shell and 0.54kGy at the innermost shell. Adding 0.1-cm of plastic wrap (PVC) and edible coating to improve dose distribution, the doses at the outermost segment were 0.52 and 0.51kGy, respectively. These results are crucial since most insects lay eggs just under the produce’s skin. For multiple product arrangement, as the number of mangoes increased, the average doses decreased. However, at both-directional irradiation, even nine mangoes were acceptably irradiated; the dose uniformity ratio was 2.26. Proper control of phytosanitary irradiation treatment is critical to ensure insect elimination while maintaining product quality.

Monte Carlo Simulation of Phytosanitary Irradiation Treatment for Mangosteen Using MRI-based Geometry

Purpose: Phytosanitary irradiation treatment can effectively control regulated pests while maintaining produce quality. The objective of this study was to establish the best irradiation treatment for mangosteen, a popular tropical fruit, using a Monte Carlo simulation. Methods: Magnetic resonance image (MRI) data were used to generate a 3-D geometry to simulate dose distributions in a mangosteen using a radiation transport code (MCNP5). Microsoft Excel with visual basic application (VBA) was used to divide the image data into seed, flesh, and rind. R adiation energies used for the simulation were 10 MeV (high-energy) and 1.35 MeV (low-energy) for the electron beam, 5 MeV for X-rays, and 1.25 MeV for gamma rays from Co-60. Results: At 5 MeV X-rays and 1.25 MeV gamma rays, all areas (seeds, flesh, and rind) were irradiated ranging from 0.3 ~ 0.7 kGy. The average doses decreased as the number of fruit increased. For a 10 MeV electron beam, the dose distribution was biased: the dose for the rind where the electrons entered was 0.45 ± 0.03 kGy and the other side was 0.24 ± 0.10 kGy. Use of an electron kinetic energy absorber improved the dose distribution in mangosteens. For the 1.35 MeV electron beam, the dose was shown only in the rind on the irradiated side; no significant dose was found in the flesh or seeds. One rotation of the fruit while in front of the beam improved the dose distribution around the entire rind. Conclusion: These results are invaluable for determining the ideal irradiation conditions for phytosanitary irradiation treatment of tropical fruit.

Phytosanitary irradiation of peach fruit moth (Lepidoptera: Carposinidae) in apple fruits

Peach fruit moth, Carposina sasakii Matsumura, is a serious pest of many pome and stone fruits and presents a quarantine problem in some export markets. It is widely distributed in pome fruit production areas in China, Japan, Korea, North Korea and the Far Eastern Federal District of Russia. In this investigation, gamma radiation dose–response tests were conducted with late eggs (5-d-old) and various larval stages, followed by large-scale confirmatory tests on the most tolerant stage in fruit, the fifth instar. The dose-response tests, with the target radiation dose of 20 (late eggs), 40, 60, 80, 100, 120, 140, and 160Gy (late fifth instars in vitro) respectively applied to all stages, showed that the tolerance to radiation increased with increasing age and developmental stage. The fifth instar (most advanced instar in fruits) was determined to be the most tolerant stage requiring an estimated minimum absorbed dose of 208.6Gy (95% CI: 195.0, 226.5Gy) to prevent adult emergence at 99.9968% efficacy (95% confidence level). In the confirmatory tests, irradiation was applied to 30,850 late fifth instars in apple fruits with a target dose of 200Gy (171.6–227.8Gy measured), but only 4 deformed adults emerged that died 2d afterwards without laying eggs. A dose of 228Gy may be recommended as a phytosanitary irradiation treatment under ambient atmosphere for the control of peach fruit moth on all commodities with an efficacy of 99.9902% at 95% confidence level.

Understanding Phytosanitary Irradiation Treatment of Pineapple Using Monte Carlo Simulation

th , 2013; Revised: May 17 th , 2013; Accepted: May 21 th , 2013 Purpose: Pineapple is now the third most important tropical fruit in wor ld production after banana and citrus. Phytosanitary irradiation is recognized as a promising alternative treatment to chemical fumigation. However, most of the phytosanitary irradiation studies have dealt with physiochemica l properties and its efficacy. Accurate dose calculation is crucial for ensuring proper process control in phytosanitary ir radiation. The objective of this study was to optimize phytosanitary irradiation treatment of pineapple in various radiation sources using Monte Carlo simulation. Methods: 3-D geometry and component densities of the pineapple, extracted from CT scan data, were entered into a radiation transport Monte Carlo code (MCNP5) to obtain simulated dose distribution. Radiation energy used for simulation were 2 MeV (low-energy) and 10 MeV (high-energy) for electron beams, 1.25 MeV for gamma-rays, and 5 MeV for X-rays. Results: For low-energy electron beam simulation, electrons penetrated up to 0.75 cm from the pineapple skin, which is good for controlling insect eggs laid just below the fruit surface. For high-energy electron beam simulation, electrons penetrated up to 4.5 cm and the irradiation area occupied 60.2% of the whole area at single-side irradiation and 90.6% at double-side irradiation. For a single-side only gamma- and X-ray source sim ulation, the entire pineapple was irradiated and dose uniformity ratios (Dmax/Dmin) were 2.23 and 2.19, respectively. Even though both sources had all greater penetrating capability, the X-ray treatment is safer and the gamma-ray treatment is more widely used due to their availability. Conclusions: These results are invaluable for optimizing phytosanitary irradiation treatment planning of pineapple.

Application of gamma irradiation on eggs, active and quiescence stages of Tetranychus urticae Koch as a quarantine treatment of cut flowers

Tetranychus urticae Koch (Tetranychidae) is amongst the most serious pests of cut flowers and ornamentals. In this research the effects of gamma irradiation on different biological stages (including quiescent stages) of this pest have been studied. Irradiation at the doses of 250, 250, 200, 250, 200, 350 and 300Gy causes sterility of females who were able to reach to adult stage from eggs, larva, protochrysalis, protonymph, deutochrysalis, deutonymph and teliochrysalis stages, respectively. The irradiation caused a decrease in percentage of mites entering the adult stage, developed the adult mite‘s longevity, number of laid eggs per adult female emerged from irradiated immature stages, and finally a retardation of embryonic and post-embryonic development. The sex ratio of the adult mites resulted from irradiated immature stages was biased towards females through increase of dose. The adult mites developed from irradiated two-day old eggs, three-day old eggs, larva, protochrysalis and deutochrysalis at 100, 350, 300, 350 and 350Gy, respectively, were 100% females. In general the females resulted from irradiated quiescent stages have shown a high sensitivity to characteristics like eggs hatchability percentage and the emerged adult's sex ratio. On the other hand with regard to percentage of immature mites developed to adult stages, longevity of adult males and females, number of eggs laid by females and the time needed to complete their development, teliochrysalis has been the most tolerant stage. Also a 300Gy dose could cause sterility in females irradiated at deutonymph stage and mated with adult males irradiated before mating and prevent their eggs to be hatched. In conclusion the most tolerance stages of this mite for most of characteristics was generally the most developed ones and a dose of around 300Gy could be a phytosanitary irradiation treatment for Tetranychus urticae Koch.