Effectiveness of Ethyl Formate as a Fumigant of Blattella germanica and Periplaneta americana (Blattodea: Ectobiidae, Blattidae) in Cross-Border Trade Transportation

Cockroaches cause problems as pests not only locally in residential areas but also internationally, as they can disperse across borders in transport vessels. We investigated the effects of the ethyl formate (EF) fumigant on all developmental stages of Blattella germanica and Periplaneta americana. For B. germanica eggs, the hatching inhibition rate increased directly proportionately with the increasing treatment concentration of EF, but the 100% control was not observed. P. americana eggs did not show any fumigation effect, even after exposure to 60 mg/L of fumigant in a 12 L desiccator. Adults and nymphs of the two species showed various fumigation effects dependent on the concentration in the 12 L desiccator. When EF was applied at the lethal concentration for 99% mortality (LCT99) values of 35 mg/L for 4 h (78.5 mg·h/L) and 60 mg/L for 2 h (70.8 mg·h/L), respectively, adults and nymphs of both species had 100% mortality in a 0.65 m3 fumigation chamber with a 20% loading ratio. However, no significant difference from the control was observed in the egg stage of either species of cockroach. The results of this experiment indicate that EF can be used as a fumigant for cross-border transport vessels if the control period occurs during the cockroach developmental stage and continuous refumigation is performed.

Synergistic Effects and Toxic Mechanism of Phosphine with Ethyl Formate against Citrus Mealybug (Planococcus citri)

Methyl bromide (MB) has been used in a wide range of applications, but since it was determined to be an ozone-depleting compound, it has only been used for pre-shipment and quarantine purposes in trade. Phosphine (PH3) is currently the ideal fumigant as an MB alternative worldwide. However, the development of PH3 resistance in the target insect pest and longer PH3 fumigation treatment times raise questions about the continued use of PH3. This study attempted to shorten treatment time via combination treatment with ethyl formate (EF). Planococcus citri was used as the main quarantine pest in Korea, and the acute toxicity of EF, PH3, and EF + PH3 was determined at every developmental stage. EF treatment at 4 h showed LCT99 values of 45.85~65.43 mg∙h/L, and PH3 treatment at 20 h showed that of 0.13~0.83 mg∙h/L depending on the developmental stage. The efficacy of PH3 decreased after reducing the treatment time, but synergistic effects were observed at all stages of development of P. citri when both fumigants were used simultaneously for 4 h. After combined treatment, dihydrolipoyl dehydrogenase expression and the production of two phospholipids, PI(O-16:0) and PC(18:2), were significantly reduced in treated P. citri adults compared with the control. Therefore, combined treatments might be key to reducing the treatment time and resistance of PH3 in the field.

Ethyl Formate as a Methyl Bromide Alternative for Fumigation of Citrus: Efficacy, Fruit Quality, and Workplace Safety

Ethyl formate (EF) was evaluated as a potential alternative to methyl bromide (MB) for phytosanitary treatment of imported citrus fruit in the Republic of Korea. Planococcus citri (Risso) (Hemiptera: Pseudococcidae), a mealybug with known tolerance against EF and MB, was used as a representative pest to test efficacy of the two fumigants against eggs. In nine commercial-scale refrigerated container (67.5 m3) trials using imported orange, lemon and grapefruit, EF applied at the currently approved dose for citrus (70 g·m-3 at 5°C for 4 h, developed for Aspidiotus excisus Green (Hemiptera: Diaspididae), a species less EF tolerant than P. citri) resulted in 76.9–98.3% 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 h) or EF treatment guidelines, the concentration of fumigant around the fruit fluctuated between 9.4 and 185.1 ppm for EF and 9.5–203.0 ppm for MB during the 72-h post-fumigation processes (venting [0–2 h], transportation to storage [2–24 h], and storage periods [24–72 h]) with both EF and MB maintained between 10 and 100 ppm during the storage period. Considering the efficacy of EF, its apparent lack of phytotoxicity, and its more manageable threshold limit value for humans (100 ppm EF compared to 1 ppm MB for an 8-h 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.

Scaled-up ethyl formate fumigation to replace methyl bromide on traded mushroom to disinfest mushroom fly (Lycoriella mali)

Mushroom fly, Lycoriella mali (Diptera: Sciaridae), is the primary pest in imported mushrooms. The amount of Tricholoma matsutake imported from China increases every fall when it is harvested. When importing T. matsutake, disinfestation using methyl bromide (MB) or phosphine (PH3) is performed to prevent the introduction of L. mali. However, MB will be phased out due to ozone-depletion, chronic toxicity to workers, and residual issues. PH3 fumigation in mushroom disinfestation requires a long exposure time (24 h). In this study, we used ethyl formate (EF), which can replace MB and reduce exposure time. The efficacy of EF, PH3 and EF + PH3 on L. mali was evaluated. Using 4-h EF fumigation at 5 °C, the 3rd and 4th instar was the most tolerant stage in terms of 99% killed lethal concentration × time products (LCt99%). When 4-h EF fumigation at 5 °C was applied on all stages of L. mali, the LCt99% values of EF were 73.1 g h/m3 to the 1st and 2nd instar, 112.9 g h/m3 to the 3rd and 4th instar, 68.9 g h/m3 to pupae, and 20.1 g h/m3 to adult. It was confirmed that combination treatment with EF + PH3 had a synergistic effect on L. mali. The LCt99% of EF + 0.5 g/m3 of PH3 to the 3rd and 4th instar was 48.3 g h/m3. When only 140 g/m3 of EF was applied for 4 h at > 5 °C and 35 g/m3 of EF + 0.5 g/m3 of PH3 for 4 h at > 5 °C in commercial trials containing T. matsutake, proven efficacy (100%) on L. mali was confirmed. In the case of EF treatment only, phytotoxic damage occurred due to high Ct products, and there was no phytotoxic damage in combination treatment with EF + PH3. This study provides a new guideline for EF + PH3 combination treatment within a shorter exposure time (4 h) than existing PH3 treatment (24 h) and replacement of MB use.

Characteristic volatile organic compounds in “HeTao” melon and other cultivars grown in Hetao region analyzed by HS-GC-IMS

The headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) was used to compare the volatile organic components of the Hetao melon and six other cultivars of melon grown in the Hetao region of China. The results showed that the common VOCs that could be qualitatively identified from the 7 different melon samples were 35 monomers and dimers of certain compounds, mainly including alcohols, esters, aldehydes, terpenes, acids and pyridines. Hexyl acetate, 3-methylbutyl acetate, ethyl acetate and ethyl formate were predominant VOCs in seven melon cultivars. Among them, Xizhoumi No. 25 (XZM25) had 3 unique volatile organic components: 3-methylbutanal, benzaldehyde and nonanal. Xizhoumi No. 17 (XZM17) had 3 unique volatile organic components: alpha-pinene, linalool and (E)-2-hexenol. Jinhongmi (JHM) had 1 unique volatile organic component: ethyl pentanoate. The Hetao melon (HLS) contained 3 unique volatile organic components: heptanal, 2-ethyl-6-methyl pyrazine and 3-methyl valeric acid. Yinmi (YM) had 2 unique volatile organic components: 3-methylbutanol and 1-butanol, and Huangjinmi (HJM) had 1 unique volatile organic component: limonene. YM, GMB2010, HLS and JHM were similar based on the principal component analysis. This research analyzed the flavor components of different melon cultivars grown in the Hetao region of China for the first time.