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Article

Ethyl Formate as a New Sanitary Treatment for Disinfesting the Hitchhiking Insect Pest Halyomorpha halys on Imported Nonfood Agricultural Machinery

by
Kyeongnam Kim
1,
Dongbin Kim
1,2,
Byung-Ho Lee
1,
Gwang Hyun Roh
3,
Kyung Won Kim
4,
Hwan-Young Jeon
5 and
Sung-Eun Lee
1,2,*
1
Institute of Quality & Safety Evaluation of Agricultural Product, Kyungpook National University, Daegu 41566, Republic of Korea
2
Department of Applied Biosciences, Kyungpook National University, Daegu 41566, Republic of Korea
3
Department of Plant Medicine, Institute of Agriculture & Life Science, Gyeongsang National University, Jinju 52828, Republic of Korea
4
Animal and Plant Quarantine Agency, Gimcheon 39660, Republic of Korea
5
Division of Automobile, Busan Institute of Science and Technology, Busan 46639, Republic of Korea
*
Author to whom correspondence should be addressed.
Appl. Sci. 2023, 13(21), 11764; https://doi.org/10.3390/app132111764
Submission received: 14 September 2023 / Revised: 22 October 2023 / Accepted: 26 October 2023 / Published: 27 October 2023
Browse Figures
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Abstract

:

Featured Application

New sanitary treatment using ethyl formate fumigation on importing/exporting agricultural machinery as an alternative to methyl bromide.

Abstract

With an increase in the international trade of agricultural and non-agricultural products, there is an increase in the possibility of introducing hitchhiking insect pests such as Halyomorpha halys, which has been detected on imported vehicles and agricultural machinery. Although methyl bromide (MB) is provisionally used to control invasive pests, it is classified as a restricted chemical owing to its potential to deplete the ozone layer and pose health risks to humans in cases of inadequate ventilation, as well as concerns regarding consumer safety. Therefore, this study investigated ethyl formate’s (EF’s) efficacy against H. halys and its efficacy and sorption, as an alternative to MB, on main electronic components, including alternators, ignition coils, and motors. Fumigation with 35 and 70 g/m3 EF for 4 h at 15 °C had no damage on the main electronic components as evaluated using various operation tests. In a commercial trial, H. halys infestation was effectively controlled with 35 g/m3 EF fumigated for 4 h at 23 °C using a 30 m3 polyvinyl chloride tarpaulin fumigation chamber. After ventilation, the EF concentration decreased below the safety level within 10 min and reached the zero level within 40 min for worker safety. This novel sanitary treatment using EF fumigation on imported agricultural machinery could be an effective method without causing mechanical damage.

1. Introduction

Currently, the amount of nonfood miscellaneous goods imported into South Korea is increasing every year. Among them, the number of quarantine cases for agricultural machinery, which is one of the major miscellaneous goods, is increasing every year, with 209 t in 2020, 752 t in 2021, and 750 t in 2022. Accordingly, the detection rate of insect pests in the inspection process is also increasing [1]. Although the import and export items for nonfood miscellaneous goods are diversifying, phytosanitary treatment standards are applied only to certain miscellaneous goods. Therefore, a new standard of phytosanitary treatment is required according to the diversification of miscellaneous goods and exotic and/or regulated pest groups (flies, moths, ants, and stinkbugs), which are primarily detected as hitchhiking on them [1].
The brown marmorated stink bug (BMSB) Halyomorpha halys (Hemiptera: Pentatomidae), one of the hitchhiking insect pests on imported nonfood miscellaneous goods, can cause severe agricultural damage [2] and urban and commercial damage because of its overwintering aggregations inside dwellings, vehicles, and consignments [3,4,5]. H. halys has 300 species of host lists [6]. It occurs primarily in fruit orchards. When H. halys is established, it rapidly becomes the dominant species, and, unlike native stink bugs such as Plautia stali and Riptortus pedestris, it is a pest that occurs throughout the entire growing season [7,8].
As the BMSB is controlled as a quarantine pest in certain countries, phytosanitary treatment of potential hosts such as plants and vehicles is essential to prevent its introduction and establishment. In particular, regarding the control of H. halys hitchhiking on imports in Australia and New Zealand, fumigation with methyl bromide (MB) and sulfuryl fluoride, as well as heat treatment, has been approved [9]. In 2010, apple orchards in the mid-Atlantic region of the United States suffered a damage of USD 37 million due to H. halys infestation, with the reported loss being >90% [10]. Furthermore, although H. halys is not a major insect pest of grapes, several hectares of grape and peach fields were lost in the United States in 2010 because of high populations of H. halys that appeared during the harvest season in the mid-Atlantic region [7,11]. Heat treatment is approved at ≥56 °C at the coldest surface of the goods for 30 min or 60 °C for 10 min [12]; however, its use is limited because it is not cost-effective and is difficult to apply on large-sized goods such as agricultural machinery [13]. In addition, MB fumigation has been prohibited in some countries according to the Montreal Protocol because of its ozone depletion properties [14].
Fumigation is primarily used in cases of stored grain infestation, soil pathogen and nematode control, and quarantine disinfestation [15,16,17]. It is an effective and economical disinfestation method to control a broad range of insect pests in tightly sealed structures. Phosphine (PH3) is a promising alternative to MB, but it causes mechanical damage such as the appearance of solid crystalline encrustations on metal and metal–textile composites, including copper, brass, silver, and iron [18]. Conversely, ethyl formate (EF) is actively being investigated as an alternative to MB because it has non-ozone-depletion properties and provides a safer working environment than MB due to its relatively low toxicity to mammals and no-residue property on commodities [19,20]. EF is generally available in liquid form and evaporates easily, eliminating the need for gaseous cylinders. Because of these advantages, studies conducted in recent years have reported that EF fumigation has been used for disinfestation purposes for various types of fruits, vegetables, nursery plants, and even nonfood commodities [20,21,22,23,24,25,26,27].
In this study, we investigated the efficacy of EF application as a disinfestation treatment against H. halys, the major hitchhiking insect pest of imported agricultural machinery. Specifically, we conducted (1) an efficacy test of EF against H. halys (>23 °C); (2) EF sorption and reactivity tests for the alternator, ignition coil, and starter motor, which are the major parts of agricultural machinery; and (3) a commercial trial using liquid EF with N2 application against H. halys on imported agricultural machinery.

2. Materials and Methods

2.1. Fumigant

Liquid EF (EF, 99% purity, FumateTM) was supplied by Safefume Inc. (Daegu, Republic of Korea). For laboratory fumigation (0.275 m3, 0.55 × 0.5 × 1.0 m) on the alternator and starter motor, liquid EF was vaporized using an EF vaporizer, which was supplied by Safefume Inc., and mixed with nitrogen carrier gas to form the nonflammable EF fumigant formulation.

2.2. Insects

Adult females and males of H. halys were captured using pheromone traps and insect collection nets in a field located in Andong, Republic of Korea, and reared on a succulent plant as the food source at 25 ± 1 °C with 60% relative humidity (RH) and 16:8 h (L:D).

2.3. Efficacy of EF against H. Halys

EF fumigation on H. halys adults was conducted using glass desiccators (Duran®, 6.8 L) with a mini fan placed at the bottom of each desiccator for inner air circulation. Insect samples were inoculated into insect breeding dishes (diameter 4.5 cm) and placed inside the desiccators. After sealing the desiccators using grease, liquid EF was injected using a gastight syringe (SGE Analytical Science, Victoria, Australia) with a scheduled dose, which was calculated using an equation reported by Ren et al. (2011) [28]. The dosage range of EF was 1.0–20.0 g/m3. The duration of fumigation was determined based on the quarantine standard of EF in South Korea and the relationship between concentration and time, as outlined in the referenced studies [29,30]. The fumigation was conducted at 23 °C for 4 h. Fumigated H. halys adults were moved to the insect rearing room after fumigation under 25 ± 2°C and 75 ± 5% RH conditions. The mortality of adults was evaluated at 72 h after fumigation, utilizing a standard criterion of determining death if there was no movement upon touch. More than 20 H. halys adults were used per replication, and all experiments were conducted in triplicates, containing a control.

2.4. Sorption Studies of EF on Alternator, Ignition coil, and Starter Motor

The EF sorption on the alternator, ignition coil, and starter motor was evaluated in a 0.275 m3 fumigation chamber. For the alternator and starter motor, 35 g/m3 EF was applied and fumigated for 4 h at 23 °C. The concentration of EF inside the fumigation chamber was determined from gas samples collected at 0.1, 1.0, 2.0, and 4.0 h after EF application using Shimadzu-GC 17A (Shimadzu, Kyoto, Japan) equipped with a flame ionization detector (FID) after separation on a DB5-MS Column (30 m × 0.25 mm i.d., 0.25 µm film thickness; J&W Scientific, Folsom, CA, USA). The oven temperature was maintained at 100 °C. The injector and detector temperatures were maintained at 250 °C and 280 °C, respectively. Helium was used as a carrier gas at a flow rate of 1.5 mL/min. The concentration of EF was calculated as the peak area against a series of external EF standards. Sorption was expressed as concentration loss ratio (C/C0), where C = EF concentration determined at one of the time intervals and C0 = EF concentration at 0.1 h.

2.5. Reactivity Test: Test Method for Determining the Electrical Characteristics of the Alternator

After the fumigation test, the alternator was left at room temperature (23 ± 2 °C) for 48 h, and, among the basic performance tests of the alternator, a rotor coil resistance test, a stator coil resistance test, and a rectifier conduction test were conducted. The test methods are described in the following sections.

2.5.1. Rotor Coil Resistance Test

The resistance between the slip ring and the slip ring was measured using a multitester, and conduction was checked. If conduction is successful, the alternator is considered normal, and if conduction is not successful, it is considered defective due to disconnection.

2.5.2. Stator Coil Resistance Test

For the stator coil resistance test, conduction was checked between the stator coil terminals using a multitester. When the coils show conduction, they are considered normal, and if there is no conduction, they are considered open circuits inside the stator coil. For the stator coil insulation test, conduction was checked between the stator coil and the stator core using a multitester. If it is not energized, it is considered normal, and if it is energized, the stator must be changed. Figure 1a shows the test method for the rotor coil and stator coil.

2.5.3. Rectifier Conduction Test

To check the (+) diode, when a (−) black probe of a multitester is connected to a diode heat sink and a (+) red probe is connected to the diode, it is a (+) diode. The reverse connection of polarity should not result in conduction. To check the (−) diode, when a (+) red probe of a multitester is connected to a diode heat sink and a (−) black probe is connected to the diode, it is a (−) diode. The reverse connection of polarity should not result in conduction. Figure 1b depicts the rectifier test method.

2.6. Reactivity Test: Test Method for Determining the Electrical Characteristics of the Ignition Coil

After the fumigation test, the ignition coil was left at room temperature (23 ± 2 °C) for 48 h, and then the primary and secondary resistance of the ignition coil single product and the ignition plug cap resistance measurement tests were performed. Figure 1c illustrates the measurement position of the ignition coil.

2.6.1. Primary Ignition Coil Resistance Measurement

The resistance between ignition coil A and terminal B was measured using a multitester. If resistance is within the reference range, it is considered normal.

2.6.2. Secondary Ignition Coil Resistance Measurement

The resistance of ignition coils A and C terminals or B and C terminals was measured using a multitester. If resistance is within the reference range, it is considered normal.

2.6.3. Ignition Pug Cap Resistance Measurement

The resistance ignition coils D and E were measured using a multitester. If resistance is within the reference range, it is considered normal. Figure 1c shows the ignition coil measurement method.

2.7. Reactivity Test: Test Method for Determining the Electrical Characteristics of the Starter Motor

The solenoid operation test and no-load test were conducted during the basic performance test of the motorized motor after leaving it at room temperature (23 ± 2 °C) for 48 h after the fumigation test. The test method is as follows.

2.7.1. Starter Motor Solenoid Operation Test

In the pull-in test of the solenoid switch, the pull-in coil is normal when the pinion gear moves outward by applying a (+) voltage to the S terminal and a (−) voltage to the M terminal of the starter motor. In the hold-in test of the solenoid switch, the hold-in coil is normal if the pinion gear is moved outward and fixed by applying a (+) voltage to the S terminal of the starter motor and a (−) voltage to the solenoid switch body. For the solenoid switch return test, a (+) voltage is applied to the S terminal, and a (−) voltage is applied to the M terminal. Then, if the M terminal (−) power is removed first and the S terminal (+) power is removed, it is normal if the pinion gear returns to its original position.

2.7.2. No-Load Operation Test of the Starter Motor

The no-load test of the starter motor implies performing an operation test without a load with the starter motor removed from the engine. The test battery capacity is 12 [V], 100 [AH]. Figure 1d illustrates the no-load operation test method. The red lead wire of the voltmeter is connected to terminal B of the starter motor, and the black lead wire is connected to terminal (−) of the storage battery by fixing the starter motor to prevent its movement. A clamp-type ammeter is installed on the wiring between the starter motor B terminal and the storage battery (+) terminal. The ignition switch is cranked by turning it to START. To reduce the load of the starter motor, the cranking time is shortened to <15 s. During cranking, the voltage drop is considered normal only when the measured voltage is ≥90% of the voltage of the storage battery. Moreover, the current consumption during cranking must be ±10% or less of the storage battery capacity.

2.8. Commercial Trial with an Evaluation of Worker Safety

A commercial-scale trial of EF fumigation of agricultural machinery was conducted using a polyvinyl chloride (PVC) tarpaulin fumigation chamber (30 m3, 6.0 × 2.0 × 2.5 m) in a warehouse located at Busan port (Busan, Republic of Korea) (Figure 2a). The agricultural machinery used in the commercial trial was a drilling machine weighing 4980 kg imported from Hong Kong. Then, 35 g/m3 EF was applied for 4 h at 23 °C. Liquid EF was vaporized with SFM (Safefume Co., Deagu, Republic of Korea) with N2 used as a carrier gas, and a fan was placed at the bottom of the PVC tarpaulin fumigation chamber for efficient gas circulation. A more-than-average amount of 180 H. halys adults were placed in three different locations (front, middle, and rear; >180 adults/location) inside the PVC tarpaulin fumigation chamber (Figure 2b). Gas samples were collected at specific time intervals (0, 1, 2, and 4 h), and EF concentration was measured using GC-FID. As it is difficult to perform GC-FID directly on the field, the EF concentration was checked in advance on the field using a gas analyzer (IBRID MX6; Industrial Scientific, Pittsburgh, PA, USA). After the completion of fumigation, H. halys adults were transferred to the insect rearing room. The mortality of H. halys adults was recorded 3 days after fumigation.
For evaluating worker safety, after the completion of fumigation, the EF concentration in the PVC tarpaulin fumigation chamber was measured at time intervals for worker safety during ventilation using a portable gas analyzer (Minirae 3000, RAE Systems, San Jose, CA, USA).

3. Results and Discussion

3.1. Efficacy of 4 h EF Fumigation against H. Halys

The lethal concentration × time (LCt)50 and LCt99 values of EF against H. halys were 15.88 and 31.51 g h/m3, respectively, for the adult stage, as determined from the fitted slopes, 7.82 ± 0.7 for 4 h fumigation at 23 °C (Table 1). A previous study confirmed that complete control (100%) of H. halys adults was achieved irrespective of whether the insect was in a diapause or nondiapause state when EF fumigation was performed at 12 g/m3 for 3 h at 10 °C and 25 °C [30]. In that study, the lethal dose (LD)99 values of EF against diapause H. halys and nondiapause H. halys were 6.41 and 4.63 g/m3 at 10 °C, respectively, and the respective values at 25 °C were 5.51 and 4.03 g/m3 [30].

3.2. Sorption Studies of EF and Reactivity Test on Alternator, Ignition Coil, and Starter Motor

The EF concentration on the alternator, ignition coil, and starter motor in the fumigation chamber remained constant during the 4 h fumigation period. For the alternator, ignition coil, and starter motor, EF applied a dose target at the LCt99 value, and the sorption of EF was approximately 5–10% at the end of fumigation (Figure 3). This sorption rate was extremely low compared with 50% in previous studies for phytosanitary purposes with plants [31,32]. This phenomenon might be related to the hydrolysis properties of EF, as EF is readily hydrolyzed to formic acid and ethanol in water or humid conditions. Therefore, this low sorption rate was suitable because machinery components do not have much water.

3.2.1. Test Method for Determining the Electrical Characteristics of the Alternator

Sample No. 1 is a control tool, Samples No. 2 and 3 are 35 g/m3, and Sample No. 4 a is 70 g/m3 EF fumigation sample. Table 2 shows the measurement results of the electrical characteristics of the treated sample with a difference in the amount of fumigation from the sample before fumigation. According to the test result, the normal conditions were satisfied (Table 2).

3.2.2. Test Method for Determining the Electrical Characteristics of the Ignition Coil

Sample No. 1 is a control tool, Sample No. 2 is 35 g/m3, and Sample No. 3 is a 70 g/m3 EF fumigation sample. Table 3 shows the measurement results of the electrical characteristics of the treated sample with a difference in the amount of fumigation from the sample before fumigation. According to the test, the normal conditions were satisfied (Table 3).

3.2.3. Test Method for Determining the Electrical Characteristics of the Starter Motor

Sample No. 1 is a control tool, Sample No. 2 is 35 g/m3, and Sample No. 3 is a 70 g/m3 fumigation sample. According to the solenoid operation test result of the starter motor, the pull-in pinion was returned to normal in the forward, hold-in pinion maintenance, and return tests for all samples 1, 2, and 3. Table 4 shows the solenoid operation test results of the start motor. According to the no-load test result of the starter motor using a battery with a capacity of 12 [V]–100 [AH], the voltage drop of samples 1, 2, and 3 was 11.38–11.49 [V], satisfying the reference value of ≥10.8 [V] (Table 5). The consumption current was 100.2–104.9 [A], satisfying the reference value of 90–110 [A] (Table 5). The measured value is considered a decrease in battery performance according to the test. Therefore, after the fumigation test, the results of the solenoid operation test and no-load test of the motor are judged to be normal, and the effect of fumigation on the basic performance of the motor is small.
Interestingly, a study reported that MB and methyl iodide (MI) exhibit sporicidal activities on electronic equipment during fumigation [33]. These two fumigants did not corrode the metal surface of the electronics, but they caused severe damage to rubber materials in the electronics. In addition to this damage, MI fumigation resulted in further damage on LCD displays [33]. Based on these results, MB fumigation, rather than MI fumigation, was suggested to control fungal contamination on electronics [33]. Compared with the results of that study, our results demonstrated that EF is a suitable fumigant to control insect infestation on imported agricultural machinery, causing small amounts of damage to machine running. Furthermore, MB use is very critical because of its ozone disruption property [34]. EF use may also contribute to controlling insect pests via fumigation during national trade.

3.3. Commercial Trial

The EF commercial trial was conducted to confirm the disinfestation of H. halys adults using a 30 m3 PVC tarpaulin fumigation chamber on agricultural machinery (drilling machine). The application of 35 g/m3 EF for 4 h at 23 °C resulted in 100% mortality among H. halys adults (566 fumigated H. halys adults were used). The Ct products of EF were 98.00 ± 1.1 g h/m3 (Table 6). We confirmed more than achievable LCt99 values, and the loss rates of EF were approximately 40% for 4 h of fumigation, which was shown in the difference to previous laboratory condition studies (Figure 4a).

3.4. Evaluation of Worker Safety in EF Fumigation

In the ventilation process, the EF concentration rapidly decreased to <100 ppm (TLV-TWA of EF) within 10 min. However, it required >1 h to decrease the hazardous conditions, which might cause unexpected acute inhalation risk in the workplace (Figure 4b).
Similarly, the ventilation of EF after fumigation does not leave residual EF inside and outside of a vinyl house [35]. When the EF concentration was measured after ventilation, it reached much less than the TLV of 100 ppm after 5 min. In the present study, it took only 10 min to reach less than the TLV of 100 ppm, and no EF residue was detected at 1 h after ventilation. In the other study, EF did not exhibit any detectable risk to the public, truck drivers, or workers from 2-day exposure [36]. EF treated in the in-transit containers or inside the cab of the truck was not detected in the environment, and there was minimal risk to workers when the containers were ventilated after a 2-day journey. However, Coetzee et al. (2019) suggested ventilation of EF after 48 h of in-transit fumigation because of the EF concentration was more than the TLV of 100 ppm [36]. As EF is used for shipment, our data suggest that it can be used to control agricultural insect pests in a vinyl house environment.

4. Conclusions

EF demonstrated excellent efficacy against H. halys adults. When the major components of agricultural machinery (alternator, ignition coil, and starter motor) were treated with EF at 35 and 70 g/m3 for 4 h at 23 ± 1 °C, there was no reactivity at levels higher than the LCt99 value of EF (31.51 g h/m3) for controlling H. halys adults. Based on the nonreactivity to the major electronic parts in the machinery after EF fumigation and the nonspecific reactivity on imported agricultural machinery in practice after EF fumigation with satisfactory results in the disinfestation of H. halys, EF fumigation might be an effective sanitary treatment method on agricultural machinery and even other vehicles and might replace the currently used MB in Korea. We strongly recommend adapting this new sanitary treatment method of EF fumigation during the export of agricultural machinery and other vehicles to other countries with quarantine concerns of the BMSB.

Author Contributions

Conceptualization, B.-H.L. and G.H.R.; methodology, K.K. and H.-Y.J.; software, D.K.; validation, K.W.K. and H.-Y.J.; formal analysis, D.K.; investigation, K.K and D.K.; resources, K.W.K.; data curation, K.K. and D.K.; writing—original draft preparation, K.K., D.K., and S.-E.L.; writing—review and editing, K.K. and S.-E.L.; visualization, K.K.; supervision, S.-E.L.; funding acquisition, B.-H.L. and G.H.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Animal and Plant Quarantine Agency (APQA) (PQ20213B050-SP).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All the data generated in this work is provided in the article.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 13 11764 g001
Figure 1. Reactivity test method for electrical characteristics. (a) Rotor coil resistance test, stator coil conduction test, and insulation test. (b) Check the (+) diode and the (−) diode. (c) Ignition coil measurement position with primary and secondary methods of ignition coil and cap resistance measurement. The primary resistance of the ignition coil was measured at positions A and B, while secondary resistance was measured at positions A and C, as well as B and C, and cap resistance was measured at positions D and E. (d) No-load test of the starting motor.
Figure 1. Reactivity test method for electrical characteristics. (a) Rotor coil resistance test, stator coil conduction test, and insulation test. (b) Check the (+) diode and the (−) diode. (c) Ignition coil measurement position with primary and secondary methods of ignition coil and cap resistance measurement. The primary resistance of the ignition coil was measured at positions A and B, while secondary resistance was measured at positions A and C, as well as B and C, and cap resistance was measured at positions D and E. (d) No-load test of the starting motor.
Applsci 13 11764 g001
Applsci 13 11764 g002
Figure 2. Photographs of commercial trials for disinfesting the hitchhiking insect pest Halyomorpha halys using ethyl formate fumigation on imported agricultural machinery. (a) A polyvinyl chloride (PVC) tarpaulin fumigation chamber. (b) Secondhand imported products infested with H. halys.
Figure 2. Photographs of commercial trials for disinfesting the hitchhiking insect pest Halyomorpha halys using ethyl formate fumigation on imported agricultural machinery. (a) A polyvinyl chloride (PVC) tarpaulin fumigation chamber. (b) Secondhand imported products infested with H. halys.
Applsci 13 11764 g002
Applsci 13 11764 g003
Figure 3. The ethyl formate (EF) sorption rate on the alternator, ignition coil, and starter motor (EF 35 g/m3 for 4 h at 23 ± 1 °C). Sorption was expressed as concentration loss ratio (C/C0), where C = EF concentration was determined at one of the time intervals, and C0 = EF concentration was determined at 0 h.
Figure 3. The ethyl formate (EF) sorption rate on the alternator, ignition coil, and starter motor (EF 35 g/m3 for 4 h at 23 ± 1 °C). Sorption was expressed as concentration loss ratio (C/C0), where C = EF concentration was determined at one of the time intervals, and C0 = EF concentration was determined at 0 h.
Applsci 13 11764 g003
Applsci 13 11764 g004
Figure 4. Sorption rate and evaluation of worker safety in commercial trial. (a) Gas concentration of ethyl formate (EF) in the commercial trial on agricultural machinery (35 g/m3 for 4 h fumigation). Sorption was expressed as concentration loss ratio (C/C0), where C = EF concentration was determined at one of the time intervals, and C0 = EF concentration was determined at 0 h. (b) EF concentration (ppm) under natural ventilation after 4 h fumigation in the commercial trial (23 ± 0.33 °C; red line indicates that the current permeable level of EF is 100 ppm).
Figure 4. Sorption rate and evaluation of worker safety in commercial trial. (a) Gas concentration of ethyl formate (EF) in the commercial trial on agricultural machinery (35 g/m3 for 4 h fumigation). Sorption was expressed as concentration loss ratio (C/C0), where C = EF concentration was determined at one of the time intervals, and C0 = EF concentration was determined at 0 h. (b) EF concentration (ppm) under natural ventilation after 4 h fumigation in the commercial trial (23 ± 0.33 °C; red line indicates that the current permeable level of EF is 100 ppm).
Applsci 13 11764 g004
Table 1. Efficacy of ethyl formate fumigation for 4 h against Halyomorpha halys adults.
Table 1. Efficacy of ethyl formate fumigation for 4 h against Halyomorpha halys adults.
Temp. (°C)1 LCt50
(95% CL 2, g h/m3)		LCt99
(95% CL, g h/m3)		Slope ± SEdfX2
2315.88
(15.09–16.69)		31.51
(28.20–36.77)		7.82 ± 0.7168.93
1 LCt: Lethal concentration × time; 2 CL: confidence level.
Table 2. Electrical characteristics of the alternator according to ethyl formate (EF) fumigation.
Table 2. Electrical characteristics of the alternator according to ethyl formate (EF) fumigation.
Fumigation ItemsMeasured ValueJudgment
Sample 1
(Control)		Rotor coilResistance test3.5 ± 0.1 [Ω]Conduction☑ Normal, □ Faulty
Stator coilConduction test☑ Conduction,□Insulation0.7 ± 0.1 [Ω]
Insulation test□ Conduction, ☑ Insulation“1” = ∞ [Ω]
Rectifier check(+) Diode☑ Normal, □ Faulty0.648 ± 0.01 [Ω]
(−) Diode☑ Normal, □ Faulty0.639 ± 0.01 [Ω
Sample 2
(EF 35 g/m3)		Rotor coilResistance test3.5 ± 0.1 [Ω]Conduction☑ Normal, □ Faulty
Stator coilConduction test☑ Conduction, □ Insulation0.8 ± 0.1 [Ω]
Insulation test□ Conduction, ☑ Insulation“1” = ∞ [Ω]
Rectifier check(+) Diode☑ Normal, □ Faulty0.626 ± 0.01 [Ω]
(−) Diode☑ Normal, □ Faulty0.637 ± 0.01 [Ω]
Sample 3
(EF 70 g/m3)		Rotor coilResistance test3.4 [Ω]Conduction☑ Normal, □ Faulty
Stator coilConduction test☑ Conduction, □ Insulation0.8 ± 0.1 [Ω]
Insulation test□ Conduction, ☑ Insulation“1” = ∞ [Ω]
Rectifier check(+) Diode☑ Normal, □ Faulty0.627 ± 0.1 [Ω]
(−) Diode☑ Normal, □ Faulty0.619 ± 0.1 [Ω]
Table 3. Electrical characteristics of the ignition coil according to ethyl formate (EF) fumigation.
Table 3. Electrical characteristics of the ignition coil according to ethyl formate (EF) fumigation.
Fumigation ItemsMeasured ValueReference ValueJudgment
Sample 1
(Control)		Ignition coil primary resistance0.8 ± 0.1 [Ω]0.7~1.2 [Ω]☑ Normal, □ Faulty
Ignition coil secondary resistance7.10 ± 0.1 [kΩ]5.0~10.0 [kΩ]
Ignition plug cap resistance5.21 ± 0.1 [kΩ]3.0~6.0 [kΩ]
Sample 2
(EF 35 g/m3)		Ignition coil primary resistance0.9 ± 0.1 [Ω]0.7~1.2 [Ω]☑ Normal, □ Faulty
Ignition coil secondary resistance7.0 ± 0.1 [kΩ]5.0~10.0 [kΩ]
Ignition plug cap resistance4.74 ± 0.1 [kΩ]3.0~6.0 [kΩ]
Sample 3
(EF 70 g/m3)		Ignition coil primary resistance0.8 ± 0.1 [Ω]0.7~1.2 [Ω]☑ Normal, □ Faulty
Ignition coil secondary resistance6.78 ± 0.1 [kΩ]5.0~10.0 [kΩ]
Ignition plug cap resistance4.71 ± 0.1 [kΩ]3.0~6.0 [kΩ]
Table 4. Solenoid operation test for the starter motor according to ethyl formate (EF) fumigation.
Table 4. Solenoid operation test for the starter motor according to ethyl formate (EF) fumigation.
Solenoid Operation TestTest Results
Sample 1
(Control)		Selonoid switchPULL-INPinion advance
HOLD-INKeep pinion forward
RETURNReturn to original position
Sample 2
(EF 35 g/m3)		Selonoid switchPULL-INPinion advance
HOLD-INKeep pinion forward
RETURNReturn to original position
Sample 3
(EF 70 g/m3)		Selonoid switchPULL-INPinion advance
HOLD-INKeep pinion forward
RETURNReturn to original position
Table 5. Voltage drop and current consumption test results of the starter motor.
Table 5. Voltage drop and current consumption test results of the starter motor.
Fumigated ItemsMeasured ValueReference ValueJudgment
Sample 1
(Control)		Voltage drop11.45 ± 0.1 [V]>10.8 [V]☑ Normal, □ Faulty
Consumption current100.2 ± 0.1 [A]90~110 [A]
Sample 2
(EF 35 g/m3)		Voltage drop11.38 ± 0.1 [V]>10.8 [V]☑ Normal, □ Faulty
Consumption current102.9 ± 0.1 [A]90~110 [A]
Sample 3
(EF 70 g/m3)		Voltage drop11.49 ± 0.1 [V]>10.8 [V]☑ Normal, □ Faulty
Consumption current104.9 ± 0.1 [A]90~110 [A]
Table 6. Mortality of Halyomorpha halys adults according to EF concentration and concentration–time (Ct) products by location after 4 h EF fumigation commercial trial in the PVC tarpaulin fumigation chamber (30 m3) on agricultural machinery at 23 ± 0.33 °C.
Table 6. Mortality of Halyomorpha halys adults according to EF concentration and concentration–time (Ct) products by location after 4 h EF fumigation commercial trial in the PVC tarpaulin fumigation chamber (30 m3) on agricultural machinery at 23 ± 0.33 °C.
Applied
Dose (g/m3)		Fumigation
Time (h)		EF Concentration (g/m3)Mortality
(Mean ± SE, %)
FrontMiddleRear
0----2.5 ± 0.5
350.135.3 ± 0.529.1 ± 0.629.6 ± 0.5100 ± 0.0
1.034.7 ± 0.526.5 ± 0.827.0 ± 0.8
2.021.5 ± 0.625.5 ± 0.523.9 ± 0.7
4.016.4 ± 0.619.0 ± 0.619.0 ± 0.6
Ct products (g h/m3)99.7 ± 0.997.7 ± 0.696.1 ± 2.1
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MDPI and ACS Style

Kim, K.; Kim, D.; Lee, B.-H.; Roh, G.H.; Kim, K.W.; Jeon, H.-Y.; Lee, S.-E. Ethyl Formate as a New Sanitary Treatment for Disinfesting the Hitchhiking Insect Pest Halyomorpha halys on Imported Nonfood Agricultural Machinery. Appl. Sci. 2023, 13, 11764. https://doi.org/10.3390/app132111764

AMA Style

Kim K, Kim D, Lee B-H, Roh GH, Kim KW, Jeon H-Y, Lee S-E. Ethyl Formate as a New Sanitary Treatment for Disinfesting the Hitchhiking Insect Pest Halyomorpha halys on Imported Nonfood Agricultural Machinery. Applied Sciences. 2023; 13(21):11764. https://doi.org/10.3390/app132111764

Chicago/Turabian Style

Kim, Kyeongnam, Dongbin Kim, Byung-Ho Lee, Gwang Hyun Roh, Kyung Won Kim, Hwan-Young Jeon, and Sung-Eun Lee. 2023. "Ethyl Formate as a New Sanitary Treatment for Disinfesting the Hitchhiking Insect Pest Halyomorpha halys on Imported Nonfood Agricultural Machinery" Applied Sciences 13, no. 21: 11764. https://doi.org/10.3390/app132111764

APA Style

Kim, K., Kim, D., Lee, B.-H., Roh, G. H., Kim, K. W., Jeon, H.-Y., & Lee, S.-E. (2023). Ethyl Formate as a New Sanitary Treatment for Disinfesting the Hitchhiking Insect Pest Halyomorpha halys on Imported Nonfood Agricultural Machinery. Applied Sciences, 13(21), 11764. https://doi.org/10.3390/app132111764

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