Comparison of methyl bromide and ethyl formate for fumigation of snail and fly pests of imported orchids

Authors: KWON, TAE HYUNG - Kyungpook National University; KIM, DONGBIN - Kyungpook National University; LEE, BYUNG-HO - Kyungpook National University; Cha, Dong; PARK, MIN-GOO - Jeonbuk National University

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2023
Publication Date: 1/10/2023
Citation: Kwon, T., Kim, D., Lee, B., Cha, D.H., Park, M. 2023. Comparison of methyl bromide and ethyl formate for fumigation of snail and fly pests of imported orchids. Insects. 14(1). Article 66. https://doi.org/10.3390/insects14010066.
DOI: https://doi.org/10.3390/insects14010066

Interpretive Summary: Snails and small flies are among the major pest groups intercepted from internationally traded orchids. Although methyl bromide fumigation (MB) has been generally used to disinfest these pests in importing countries, there have been anecdotal evidence that the MB treatment often resulted in severe damage on treated orchids. As a first step to develop MB alternative treatment for orchids, researchers at the USDA-ARS laboratory in HI, and Kyungpook and Jeonbuk National University in South Korea are testing whether ethyl formate (EF) fumigation is as effective as MB for snails and small flies and less phytotoxic to orchids than MB. In commercial-scale trials using four species of imported orchids, EF fumigation was as effective as MB for controlling giant African snail juveniles and mushroom fly larvae and less phytotoxic to treated orchids than MB, suggesting that EF may be applicable for the disinfestation of exotic snails and flies infesting imported orchids.

Technical Abstract: Invasive snails and flies are among the major groups of pests intercepted from imported orchids, which has been 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 instar of Lycoriella mali. Efficacy trials showed that EF was at least as effective as MB with LCt99 (lethal concentration x time product required for 99% mortality) values of EF at 68.1 and 73.1 g h/m3 at 15' and LCt99 of MB at 95.9 and 78.4 g h/m3 at 15' for A. fulica and L. mali, respectively. In scale-up trials, EF treatment at 35 g/m3 for 4 h at 15' resulted in complete control of A. fulica and L. mali. The MB treatment based on the current treatment guideline for imported orchids (48 g/m3, 2 h at >15 ') 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 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 result suggests that EF is as effective as MB to 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 in imported orchids.