Postharvest treatment of mandarin fruit using a combination of methyl bromide and phosphine against Bactrocera dorsalis (Diptera: Tephritidae)

BACKGROUND Chinese Nanfeng mandarin (Citrus reticulate Blanco '2-6') fruit is host to the oriental fruit fly Bactrocera dorsalis Hendel, and therefore requires phytosanitary treatment before exporting abroad. The use of methyl bromide (MB) should be reduced because it has phytotoxic and ozone depleting properties. In the present study, fumigations with mixtures of gaseous phosphine (PH3) and MB were conducted to disinfest B. dorsalis. The effect of combined fumigation on postharvest quality of Nanfeng mandarin fruit was then evaluated. RESULTS There was a clear synergistic effect between MB and PH3 against B. dorsalis at 20 degrees C. The third-instar larvae of B. dorsalis were the most tolerant to treatment with both MB alone and combined with PH3. Toxicity assay of third instars indicated that higher PH3 concentrations increased MB toxicity, and 1.42-2.84 g m(-3) of PH3 was optimal when combined with MB. Probit analysis showed that, combined with 2.13 g m(-3) PH3, similar mortality was achieved with 50% of the MB required when applied alone. Furthermore, the fruit quality test showed that MB fumigation resulted in a higher respiration rate and >40% fruit rot after storage. The combined treatment reduced these effects and did not have adverse effects on fruit firmness, soluble solid content, titratable acidity, or vitamin C content. CONCLUSION Our findings demonstrate the synergistic effect between PH3 and MB and indicate that this treatment has potential as a novel strategy for postharvest control of B. dorsalis, especially in MB-sensitive fruit. (c) 2019 Society of Chemical Industry