Efficacy of the fumigants sulfuryl fluoride and ethyl formate for quarantine treatment of the wood-boring pest Monochamus alternatus (Coleoptera: Cerambycidae) and comparison with fumigation of the stored grain pest Rhyzopertha dominica (Coleoptera: Bostrichidae)

Methyl bromide (MB) is a primary fumigant for wood quarantine in Korea. Due to international regulations targeting ozone-depleting and toxicity effects of MB, alternative fumigants are required. The study assessed the insecticidal and synergistic effects of sulfuryl fluoride (SF) and ethyl formate (EF), alone and in combination, against the long horned wood-boring beetle Monochamus alternatus and for comparison the lessor grain borer, Rhyzopertha dominica; combined fumigation in up-scaled conditions informed phytosanitary treatment standards. Individual treatments at 23 °C indicated 99% lethal concentration × time (LCt_99%) products of 3,933.0 mg h/liter for the most tolerant M. alternatus eggs to SF. R. dominica eggs exhibited greater tolerance to EF than M. alternatus and the pupae were the most tolerant (EF LCt_99%: 1,057.0 mg h/liter). The mixed treatment applied with EF for egg control and SF for pupal control. Mixed treatments with adjusted Ct values showed synergistic ratios ≤1.0 across most combinations, indicating no additive or synergistic interactions. The combined SF+EF application achieved complete mortality in all R. dominica life stages at a dosage of 20 + 150 mg/liter for 24 h. Concentration × Time (Ct) product of the SF+EF combination was calculated to be 629.7 + 630.9 mg h/liter, with effective control of R. dominica at a lower dosage than individual treatments, indicating its applicability to M. alternatus. This approach may represent a promising phytosanitary treatment standard for MB replacement.