Assessing the effectiveness of phosphine fumigation and cold treatment for controlling Carposina sasakii on apples

The rise of international fruit trade risks spreading pests like the peach fruit moth, Carposina sasakii Matsumura (Lepidoptera: Carposinidae), which poses a quarantine threat to Korea's apple exports. Environmental concerns limit methyl bromide (MeBr) use due to ozone depletion. This study assessed the efficacy of phosphine (PH₃) fumigation, cold treatment, and their combination—PH₃ fumigation followed by cold treatment—on fifth-instar larvae of this pest. At 2 mg/L, PH₃ fumigation caused complete mortality after 72 h at 23 °C and after 240 h at 5 °C. The LCt₅₀ and LCt₉₉ values at 23 °C were 73.98 and 212.38 mg h/L, respectively, with higher values (238.74 and 562.62 mg h/L) at 5 °C. Cold treatment at 1 °C resulted in 100% mortality after 20 d. The phytotoxic effects of PH₃ fumigation conducted at 23 and 5 °C were evaluated after 28 d of storage at 1 °C. Fruit quality declined when apples were fumigated with 4 mg/L PH₃ at 23 °C for 72 h, but no noticeable damage occurred when 2 mg/L PH₃ was used at 5 °C for 240 h. Moreover, 100% mortality under laboratory conditions was achieved by combining LCt₅₀ PH₃ fumigation with LT₃₀ cold treatment, which, compared to each treatment alone, shortened exposure time to 6 and 5 d, respectively. PH₃ sorption tests showed fumigant Ct at 23 and 5 °C across apple loading ratios (0, 10, and 25% (w/v)) did not differ significantly. These findings support developing alternative quarantine disinfestation methods to replace MeBr in apple exports.