Ethyl formate as a methyl bromide alternative for fumigation of citrus: Efficacy, fruit quality, and workplace safety

Authors: PARK, MIN-GOO - Animal And Plant Quarantine Agency; LEE, BYUNG-HO - Gyeongsang National University; YANG, JEONG-OH - Animal And Plant Quarantine Agency; KIM, BONG-SU - Animal And Plant Quarantine Agency; ROH, GWANG HYUN - Oak Ridge Institute For Science And Education (ORISE); Kendra, Paul; Cha, Dong

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2021
Publication Date: 10/8/2021
Citation: Park, M., Lee, B., Yang, J., Kim, B., Roh, G., Kendra, P.E., Cha, D.H. 2021. Ethyl formate as a methyl bromide alternative for fumigation of citrus: Efficacy, fruit quality, and workplace safety. Journal of Economic Entomology. 114(6):2290-2296. https://doi.org/10.1093/jee/toab175.
DOI: https://doi.org/10.1093/jee/toab175

Interpretive Summary: Methyl bromide (MB) has been routinely used for the disinfestation of U.S. imported citrus fruits in South Korea. However, alternative treatment of MB is necessary to address its impact on ozone layer depletion and workplace and consumer safety issues associated with MB desorbed from and residues remained in the treated fruit. International team of researchers at the USDA-ARS laboratories in Hilo, HI and Miami, FL; Gyeongsang National University and Animal and Plant Quarantine Agency in South Korea have been developing MB-alternative fumigation treatments for imported citrus in South Korea. In 40-ft reefer container fumigation trials at a commercial fumigation facility, ethyl formate (EF) showed similar efficacy as shown from previous EF and MB comparative studies on citrus mealybug, a representative tolerant insect for both EF and MB treatments. There were no apparent phytotoxicity on EF treated imported orange, lemon and grapefruit in terms of sugar content and color of fruit peel and pulp. More importantly, the concentration of EF could be maintained well below the threshold limit value of EF (100 ppm) inside the storage facility with EF treated citrus, while the lowest concentration of MB was still up to 9x greater than the threshold limit value of MB (1 ppm). Our results based on efficacy, phytotoxicity and workplace safety suggest that EF may be a promising alternative to MB for the phytosanitary treatment of imported citrus in Korea.

Technical Abstract: We evaluated ethyl formate (EF) as a potential alternative to methyl bromide (MB) for phytosanitary treatment of imported citrus fruit in the Republic of Korea. We fumigated eggs of Planococcus citri (Risso) (Hemiptera: Pseudococcidae), a mealybug with known tolerance against EF and MB, as a representative pest to test efficacy of the two fumigants. In nine commercial scale trials (67.5 m3) using imported orange, lemon and grapefruit, EF applied at the currently approved dose for citrus (70 g·m-3 at 5°C for 4-hr, developed for Cyanotis scale, a species less EF tolerant than P. citri) resulted in 76.9 to 98.3% mortality of P. citri eggs. The EF treatment did not affect the sugar content or the color of peel and pulp of the treated fruit. When oranges were treated according to the current MB (64 g m-3 at > 5°C for 2-hr) or EF treatment guidelines, the concentration of fumigant around the fruit fluctuated between 9.4-185.1 ppm for EF and 9.5-203.0 ppm for MB over the 72-hr post-fumigation processes, which included venting (0-2 hr), transportation to storage (2-24 hr) and storage periods (24-72 hr), with both EF and MB ranging between 10-100 ppm during the storage period. Considering the efficacy of EF, its apparent lack of phytotoxicity, and its more manageable threshold limit value (100 ppm EF compared to 1 ppm MB for an 8-hr time weighted average exposure), our results suggest that EF may be a promising alternative to MB for the phytosanitary treatment of imported citrus in Korea.