Qing-Ying Zhao

BACKGROUND: Paracoccus marginatus is a regulated, highly invasive pest that poses a significant risk to papaya production and international trade, necessitating effective phytosanitary disinfestation measures. Hot‐water treatment (HWT) is widely recognized as a residue‐free alternative to chemical fumigation; however, its operational schedules require alignment between pest thermal tolerance and fruit quality. In this study, the thermal tolerance of developmental stages of P. marginatus was quantified, and candidate HWT regimes were evaluated based on thermal tolerance determined on a surrogate host (sprouting potato), while papaya physiological and sensory responses were assessed separately. RESULTS: Eggs exhibited the highest heat tolerance among developmental stages and were therefore used as the conservative biological endpoint for treatment optimization. Time–mortality analysis and large‐scale confirmatory trials conducted on sprouting potato demonstrated that immersion at 49 °C for 22 min, or 47 °C for 81 min, achieved complete mortality of P. marginatus . Fruit quality assessments indicated that optimized HWT regimes delayed ripening, reduced decay incidence, and maintained firmness, color, and sensory acceptability during storage, whereas prolonged exposure at lower temperatures induced cumulative physiological stress. CONCLUSION: By combining pest mortality data from sprouting potato with papaya fruit tolerance limits, this study identifies candidate temperature–time parameters that may achieve phytosanitary security while preserving papaya fruit quality. The results provide a practical basis for developing heat treatment schedules consistent with the International Standards for Phytosanitary Measures. © 2026 Society of Chemical Industry.

Irradiation combined with Modified Atmosphere (MA) Packaging (MAP) is increasingly applied to disinfest fresh harvested produce while maintaining quality. However, anoxia and hypoxic conditions created by MA can reduce the effectiveness of ionizing radiation by inducing radioprotective effects in insects. This study investigated the relationship between oxygen levels and radiation efficacy in late third-instar larvae of Zeugodacus cucurbitae. Larvae were sealed in MAP bags filled with various low-oxygen atmospheres (0% to 5%, nitrogen balance) or ambient air (21%) and irradiated with X-rays at doses from 16 to 88 Gy. Mortality was assessed based on adult emergence. Results showed that mortality significantly decreased as oxygen level increased from 0% to 3%, and statistic data-analysis including probit analysis showed a critical oxygen threshold at 4% O₂. At oxygen levels below this threshold, significantly higher radiation doses were required to achieve 99.9968% mortality at a 95% confidence level (probit-9 level). The additional dose needed under 0% O₂ was estimated at 13–18 Gy compared to ambient air. These findings further demonstrate that phytosanitary irradiation under MA conditions can effectively control tephritid insects while preserving product quality. Identifying 4% O₂ as the radioprotective threshold may have implications for understanding dose–response mechanisms under MA conditions.

The spotted wing drosophila, Drosophila suzukii (Matsumura), is currently distributed in the main soft-skinned fruits production areas in China and 59 other countries, presenting a significant threat to importing nations. Optimal phytosanitary treatments, including fumigation, irradiation, and cold treatment, have been developed to prevent the international movement of this invasive fly. To determine the most cold-tolerant stage and facilitate the development of the technical schedules requested by the Technical Panel on Phytosanitary Treatment (TPPT), cold treatments of D. suzukii immature stages in ‘Red Globe’ grapes were conducted. Dose–mortality data at 0 °C and 2 °C from repeated trials were subjected to analysis of covariance, linear regression, and probit analysis. Results identified 3 d old pupae as the most cold-tolerant stage, followed by 1 d old pupae, 4 d old larvae, and 6 h old eggs with similar tolerance. The 2 d old larvae were the most sensitive stage. In subsequent confirmatory tests, 3 d old pupae were subjected to cold treatment at 0 °C for 9 and 10 days, and at 2 °C for 10 and 12 days, based on the probit estimation of the probit-9 value. No adult emergence occurred in the confirmatory tests except for one deformed adult from a 2 °C 10 d treatment. Therefore, the recommended treatment schedule requires fruit temperatures below 0.00 °C (or 1.62 °C) for no less than 10 (or 12) continuous days, with treatment efficacy not less than 99.9960% (or 99.9955%) at a 95% confidence level, respectively. These schedules are intended for submission to TPPT for the development of phytosanitary treatment standards.

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 LD_99.9968 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.

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 LD_99.9968 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.

The papaya mealybug Paracoccus marginatus is an invasive, polyphagous pest and poses a quarantine threat to tropical and subtropical countries. Infested commodity internationally should be undergoing phytosanitary treatment, while irradiation is recommended to replace methyl bromide fumigation. Dose-response tests were conducted on the 2-, 4-, and 6-d-old eggs and gravid females of P. marginatus using the X-ray radiation doses of 15–105 Gy with an interval of 15 Gy, respectively. Radiotolerance was compared using fiducial overlapping and lethal dose ratio (LDR) test, resulting in insignificant difference except for LDR test at LD90 (leading 90% mortality at 95% confidence level (CL)); the estimated dose for 99.9968% mortality at 95% CL was 176.5–185.2 Gy, which was validated in the confirmatory tests using gamma irradiation because gammy and X-rays have equal biological effect on pests. Therefore, a total of estimating 60,386 gravid females of papaya mealybug irradiated with 146.8–185.0 Gy resulted in no F1 nymphs developing. Eggs can therefore be used as an alternative to gravid females for dose-response tests; the recommended minimum dose for phytosanitary treatment of P. marginatus on infested commodity is 185 Gy, with treatment efficacy ≥ 99.9950% at 95% CL.

The khapra beetle, Trogoderma granarium Everts, is defined as one of the most important quarantine pests globally, and fumigation with methyl bromide, an ozone-depleting substance, is a common phytosanitary measure currently used. The modified atmosphere (MA), irradiation, and their combination treatments of T. granarium larvae and adults were performed at room temperature (24–26 ℃) to develop an ecofriendly phytosanitary disinfestation measure and to shorten the exposure time and overcome treatment disadvantages of irradiation. Late-stage larvae are determined as the most tolerant stage resulted in large LT_99.9968 values of 32.6 (29.2–37.5) and 38.0 (35.1–41.7) days treated under 1% and 2% O₂ (with N₂ balance) atmosphere, respectively. Ionizing radiation was used to enhance the effect of MA and the mortality was highly significantly affected by all the interaction effects, indicating that the synergistic effects present in all the combined treatments. The synergistic ratios, which is defined as the estimated lethal time for MA treatment (LD₉₀, LD₉₉, and LD_99.9968), divided by that of combined treatment, were between 1.47 and 2.47. In the confirmatory tests, no individuals recovered from a sum of 111,366 late-stage larvae treated under 1% O₂ atmosphere for 14- or 15-d after 200 Gy irradiation, which resulted in validating the probit estimations and achieving an efficacy of 99.9973% mortality at 95% confidence level. Therefore, these treatment schedules are recommended to disinfest T. granarium infecting commodities for phytosanitary purposes under the warehouse, MA packaging, or in combination with international transportation by train or sea container.