Comparison of Methyl Bromide and Ethyl Formate for Fumigation of Snail and Fly Pests of Imported Orchids

SIMPLE SUMMARY: Invasive snails and flies are among the major groups of pests intercepted from imported orchids in Korea, which are controlled by methyl bromide (MB) fumigation. As a first step to develop an alternative treatment, we compared the efficacy and phytotoxicity of ethyl formate (EF) and MB on four species of imported orchids using juvenile stages of Achatina fulica and third and fourth instars of Lycoriella mali. Efficacy trials showed that EF was at least as effective as MB with LCt(99) (lethal concentration × time product required for 99% mortality) values of EF at 68.1 and 73.1 g h/m(3) at 15 °C and LCt(99) of MB at 95.9 and 78.4 g h/m(3) at 15 °C for A. fulica and L. mali, respectively. In scale-up trials, EF treatment at 35 g/m(3) for 4 h at 15 °C resulted in complete control of A. fulica and L. mali. MB treatment based on the current treatment guideline for imported orchids (48 g/m(3), 2 h at >15 °C) resulted in complete control of L. mali but not A. fulica, which could be completely controlled with 3 h treatment. Leaf chlorophyll contents and hue values of treated orchids were not affected by EF treatment but were significantly changed by MB. All four species of orchid died within 30 d of MB treatment, while only one species could not recover the damage from EF treatment. Our results suggest that EF is as effective as MB for snails and flies and less phytotoxic than MB to imported orchids and may be applicable as an alternative to MB in phytosanitary treatments of invasive snails and flies of imported orchids. ABSTRACT: Invasive snails and flies are major pests of imported orchids, controlled by methyl bromide (MB) fumigation in Korea. We compared the efficacy and phytotoxicity of ethyl formate (EF) and MB on four species of imported orchids using juvenile stages of Achatina fulica and third and fourth instars of Lycoriella mali. EF was as effective as MB. The LCt(99) values of EF were 68.1 and 73.1 g h/m(3) at 15 °C; and those of MB were 95.9 and 78.4 g h/m(3) at 15 °C for A. fulica and L. mali, respectively. In the scale-up trials, EF treatment at 35 g/m(3) for 4 h at 15 °C resulted in complete control of both pests. MB treatment based on the current treatment guidelines for imported orchids (48 g/m(3), 2 h, at >15 °C) resulted in complete control of L. mali but not of A. fulica. Chlorophyll content and hue values of treated orchids were not affected by EF treatment but significantly changed by MB (p-value < 0.05). All four treated species of orchids died within 30 d of MB treatment, while only one species died from EF treatment. Our results suggest that EF is a potential alternative to MB in phytosanitary treatment of imported orchids.