Quarantine vapor heat treatment of papaya fruit for bactrocera dorsalis and Bactrocera cucurbitae (Diptera: Tephritidae)

Abstract

The presence of quarantine insect pests in fruit export can impede trade with other countries. Therefore, to reduce the risk of possible quarantine pests in exported fruit, postharvest disinfestation treatment is essential. This study investigated the effects of vapor heat treatment (VHT) on oriental fruit fly (Bactrocera dorsalis Hendel (Diptera: Tephritidae)) and melon fly (Bactrocera cucurbitae Coquillett (Diptera: Tephritidae)) which are major pests for papaya fruits. For inoculated papaya fruits weighing 550 ± 100 g, the optimal egg-inoculation density, rearing conditions, and heat tolerance for each developmental stages of both fruit flies were determined, and then analyzed to determine their survival, and assess papaya fruit quality after treatment. Result of VHT of each developmental stage indicated that the eggs of B. dorsalis were the most heat tolerant at 45.6°C. Efficacy test that determined the optimal mortality temperature was performed by subjecting 60 fruits infested with 4,500 eggs to fruit core temperatures of 44.2, 45.2, 46.2, and 47.2°C. It was found that when the papaya fruit core temperature increased at a heating rate of 0.0925°C/min from room temperature to 47.2°C in 3 h, fruit flies showed 100% mortality. Results of the confirmatory test using 300 papaya fruits also indicated 100% mortality at this temperature. Both fruit quality and injury test results demonstrated insignificant differences in color, appearance, soluble solids, or firmness of fruits before and after treatment. Thus, VHT effectively disinfested papaya fruits against both fruit fly species, thus making it a viable quarantine treatment for papaya fruits prior to their export.