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Article

Ethyl Formate-Based Quarantine Treatment for Exotic Ants and Termites in Imported Rubber Plants and Stone Products

by
Dongbin Kim
1,
Tae Hyung Kwon
1,
Min-Goo Park
2,
Kyung Won Kim
3,
Dong H. Cha
4 and
Byung-Ho Lee
1,4,*
1
Institute of Quality and Safety Evaluation of Agricultural Products, Kyungpook National University, 80 Daehak-ro, Daegu 41566, Korea
2
Department of Bioenvironmental Chemistry, Jeonbuk National University, Jeonju 54896, Korea
3
Animal and Plant Quarantine Agency, Gimcheon 39660, Korea
4
US Pacific Basin Agricultural Research Center, USDA-ARS, Hilo, HI 96720, USA
*
Author to whom correspondence should be addressed.
Appl. Sci. 2022, 12(12), 6066; https://doi.org/10.3390/app12126066
Submission received: 9 May 2022 / Revised: 7 June 2022 / Accepted: 11 June 2022 / Published: 15 June 2022
(This article belongs to the Special Issue Good Agricultural Practices: Application, Monitoring and Ecotoxicological Effects in Pesticide Use)
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Abstract

:
Exotic ants and termites, including Solenopsis invicta, are frequent hitchhikers intercepted from miscellaneous nonfood commodities. In particular, S. invicta has been intercepted in Korea in imported nursery plants, stone, and lumber products, which increases the potential for establishment of this destructive invasive pest in Korea. In this study, we conducted commercial-scale fumigation trials to evaluate ethyl formate (EF) as a potential alternative of methyl bromide using two species of imported rubber plants and pieces of marble as representative good and workers of Reticulitermes speratus as an EF-resistant surrogate for S. invicta. An EF treatment at 35 g/m3 for 4 h at >15 °C, the dose required for LCt99% (lethal concentration × time product required for 99% mortality of R. speratus), resulted in the complete control of R. speratus workers tested with rubber plants (Ficus benghalensis and F. retusa) and marble, 9% (w/v) and 60% (v/v) loading ratios, respectively. EF treatment did not adversely affect the leaf chlorophyll content, leaf color, and overall health of rubber plants or the visual appearance of the marble. Our results suggest that EF fumigation is a potential alternative to methyl bromide for the disinfestation of hitchhiking invasive termites and ants, including S. invicta, on imported rubber plants and stone products.

1. Introduction

With the increase in global trade, the introduction and establishment of new exotic pests have been on the rise, and such invasions can seriously disrupt international trade [1,2]. In Korea, the number of quarantine cases imposed on trade increased by 11.8% in a year, from 5274 cases in the first six months of 2019 to 6214 cases during the same period in 2020 [3]. Thus, there is a critical need to develop new treatment guidelines that can effectively control these pests in traded goods. The need appears to be especially strong for additional treatments for imported miscellaneous nonfood products. Despite the increases in the trade of such nonfood items [4], the number of pest groups that are regulated by disinfestation guidelines is much lower for nonfood products than that for agricultural products [3]. This has raised serious biosecurity concerns in terms of trading nonagricultural commodities [5].
The most prevalent exotic pests intercepted in imported miscellaneous goods are hitchhiking insects, including various species of ants, termites, moths, and hemipterans, many of which had not been reported in Korea [6]. On imported lumber, stone, and nursery products, the main problem has been hitchhiking ants and termites [6], which in 2020 caused up to 1% rejection of imported stone and rubber plants (27,185 and 1231 tons, respectively) [7]. The major concern has been the presence of Solenopsis invicta Buren (Hymenoptera: Formicidae), imported red fire ant, among the intercepted exotic ants and termites [8,9]. This ant species is one of world’s most aggressive and destructive invasive pests [10,11], causing a wide range of economic and ecological problems once it is established [12,13]. Native to South America, S. invicta has invaded and established in many different countries, including Australia, China, Taiwan, and the United States [14]. It was first detected in Korea in 2017, and has been detected 14 times as of 2021 around importation points, such as ports, and as hitchhikers in imported lumber, stone, and nursery plants [3].
Fumigation is an effective and economical disinfestation method to control exotic pests on various imported commodities [15,16,17] including nonfood products [9,18,19]. Methyl bromide (MB) has been widely used for such purposes, including ants and termites on imported nonfood commodities. For example, in Korea, the disinfestation of termites and ants on nonfood commodities currently relies on a blanket provisional treatment of 48 g/m3 MB at >15 °C for 24 h (T500-15) [3]. Imported lumber is an exception, which is treated by 24 h fumigation of 25~33 g/m3 MB at >10 °C or 32~49 g/m3 MB at >5 °C for termites and ants, respectively, depending on international regulations on lumber treatment (T400-1) [3]. Although most MB uses have been phased out due to its adversary effect on ozone layer depletion and human health [20,21,22,23], a critical use exemption still allows for MB fumigation for quarantine and pre-shipment purposes. Therefore, there is a critical need to develop MB-alternative disinfestation treatments. Ethyl formate (EF) is an MB alternative initially developed as a stored dried fruit fumigant in 1929 [24], and is considered to be a safe and effective alternative to MB [25,26,27] with no residues in commodities [28]. Recently, EF has been effective at controlling S. invicta [8], and an EF-based treatment (140 g/m3 at >5 °C for 4 h) was developed for the control of S. invicta in imported lumber using Reticulitermes speratus, the Japanese termite, as a resistant surrogate of S. invicta [9]. Since lumber and other nonfood commodities have different MB treatment requirements as indicated above, in this study, we tested the potential of using EF to disinfest S. invicta on some of major nonlumber nonfood commodities, such as imported stone and nursery products.
Here, we evaluate the efficacy of EF as a disinfestation treatment intended for use against S. invicta in imported stone and nursery plants. As S. invicta is not established in Korea, we used R. speratus as an EF-tolerant surrogate for S. invicta [9]. Specifically, we (1) determined EF sorption in imported rubber plants and marble, (2) conducted commercial-scale trials using a tarpaulin tent on imported rubber plants and marble, and (3) evaluated the effect of EF fumigation on quality of rubber plants and marble.

2. Materials and Methods

2.1. Insect and Chemical

Reticulitermes speratus, the Japanese termite, was collected from the Wora Mountain in Jinju, Gyeongnam, Korea in 2019 and reared on pine wood chips in an insect rearing room at Gyeongsang National University at 24 °C, 60–70% relative humidity (RH), and 16 h:8 h (L:D) light cycle [9]. EF (Fumate, 99% purity) was supplied by Safefume Co. in Hoengseong, Korea.

2.2. Rubber Plants and Stone Product

Two species of rubber plants, Ficus benghalensis and F. retusa, were purchased directly from an importer in Incheon, Korea, and used for fumigation trials and quality evaluation. They were imported as potted plants in 15 L pots containing cocopeat as the soil-less potting medium, and were 60–100 cm in height with <10 young leaves. As rubber plants are generally imported with only several young leaves, importers increase the value of rubber plants by allowing them to grow more (a minimum of 30 days or up to 6–24 months) before delivery to consumer markets. For the stone product fumigation experiment, rectangular pieces of marbles (2.8 × 2.5 × 1.5 m/piece) were provided by an importer in Busan, Korea.

2.3. Sorption Studies of EF on Rubber Plants and Marble

The evaluation of EF sorption in imported rubber plants and marble was conducted in a 0.275 (0.5 × 0.4 × 1.3 m) m3 fumigation chamber and 6.8 L desiccators, respectively. Loading ratios (w/v) of 5% rubber plants and 70% marble (cut to 20 cm piece) were selected on the basis of the currently used loading ratio for imported rubber plants and stone products during MB based commercial fumigation. For rubber plants, after sealing the fumigation chamber, 35 g/m3 of EF was applied and held for 4 h at >15 °C. For marble, after sealing the desiccator, 35, 53, and 70 g/m3 of EF were applied and held for 4 h at >15 °C. Concentrations of EF inside the desiccator or chamber were determined from gas samples collected at 0.1, 1.0, 2.0, and 4.0 h after EF application using a 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 250 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.

2.4. Commercial-Scale Trial Using Imported Rubber Plants

Commercial-scale EF fumigation trials on two species of rubber plants were conducted in a PVC tarpaulin tent (7.2 m3) in a warehouse at Incheon port (Incheon, Korea). The lips of the tent were sealed to the floor using duct tape to keep the EF gas from escaping. Access to surrounding areas of the fumigation tent was restricted during EF treatment. The tarpaulin fumigation tent was filled with 9% (w/v) loading ratio for the two species of potted rubber plants (4% of Ficus benghalensis and 5% of F. retusa). About 800 R. speratus workers in screened plastic breeding dishes (9 × 4 cm) were placed in three different locations inside the tent (front, middle, and rear parts of the tent). EF was applied at 35 g/m3 for 4 h at 15 ± 1 °C. Liquid EF was vaporized using a commercial EF vaporizer (SFM-II; supplied by Safefume Co.), and the vaporized EF gas was delivered into the fumigation tent using nitrogen gas as a propellent. To calculate Ct products, the concentration of EF inside the tent was determined at 0.1, 1.0, 2.0, and 4.0 h after EF gas had been applied. Gas samples were collected in Tedlar bags (1 L, SKC), and analyzed for EF using GC-FID as described above. At the conclusion of the fumigation trial, R. speratus in breeding dishes were transferred to an insect rearing room (>15 °C), and the mortality of R. speratus was determined three days after fumigation by visual inspection of movement and probing. Three EF fumigation trials and one untreated control were conducted. The total number of R. speratus tested was 3110. Zero mortality of R. speratus workers was observed in the untreated control.

2.5. Commercial-Scale Trial Using Imported Stone Product

A commercial-scale trial of EF fumigation of a marble product was conducted using a PVC tarpaulin tent (33.6 m3) in a warehouse located at Busan port (Busan, Korea). Similar fumigation approaches and conditions descried for rubber plants were also used for marble, except that the treatment was conducted at 13 ± 1 °C and with 60% loading ratio (v/v) of marble. Due to the difficulty of measuring the weight of large marble pieces, 60% (v/v) loading ratio was estimated from the 70% (w/v) loading ratio used in the sorption study. Two pieces of marble (2.8 m × 2.5 m × 1.5 m = 10.5 m3/piece) were used to achieve 60% (v/v) in 33.6 m3 tent. An average of 660 R. speratus workers were placed in three different locations (front, middle, and rear; ~220 workers/location) inside the tent. Ct products of EF and the mortality of R. speratus were determined as described above. Three EF fumigation trials and one untreated control were conducted. The total number of tested R. speratus was 2645. Zero mortality of R. speratus was observed in the untreated control trial.

2.6. Effect of EF on the Quality of Rubber Plants and Marble

The evaluation of potential phytotoxicity on rubber plants from the 4 h EF treatment was evaluated. The same rubber plants from the EF and the untreated control in the commercial-scale trials were used for quality evaluation. At the completion of the EF treatment and ventilation cycle, the potted plants were transferred to a greenhouse (27 ± 1 °C and 50–70% relative humidity) and allowed to grow for 30 days. Then, leaf chlorophyll contents, leaf hue values, and overall damage were evaluated at the 30th day in the greenhouse. Chlorophyll contents of 10 leaves were evaluated using a chlorophyll meter (SPAD- 502 Plus, Minolta, Tokyo, Japan) [18]. The leaf color of 10 rubber plants was measured as Hunter L, a, b values using colorimeter and expressed as hue values based on hue = [L2 + a2 + b2]/2 (TES 135A, Electrical & Electronic Corp., Taipei, Taiwan). Overall plant injury was scored using the following scale: 0 (no leaf damage), 1 (<5% of total leaves/plant dropped, browned, or shriveled), 2 (5–25% leaves affected), 3 (25–50% leaves affected), 4 (>50% leaves affected). The marbles from the commercial-scale trial were visually inspected to determine any potential effect of EF treatment on the visual quality of the marble.

2.7. Statistical Analysis

The differences of EF loss rates at different time intervals in sorption tests were analyzed using a t-test (SAS ver. 9.4) [29] between the two rubber plant species trials, and among the three trials with different EF doses for marble. The differences in the effects of EF treatment on the quality of rubber plants were analyzed using a t-test [29].

3. Results and Discussion

3.1. Sorption Studies of EF on Imported Rubber Plants and Stone Product

The concentration of EF in the chamber gradually decreased during the 4 h fumigation periods with imported rubber plants and marble (Figure 1 and Figure 2). For rubber plants, with a 5% loading ratio (w/v) and an EF treatment dose set at the LCt99% level, the sorption of EF was reduced about 40% at the conclusion of the fumigation treatment, with no differences in the rates of EF sorption between the two rubber plant species (Figure 1). For marble with a 70% loading ratio (w/v), the sorption of EF was about 30% at the conclusion of the fumigation treatment, with no differences among sorption rates from three different EF dose trials (Figure 2).
In previous studies on food and nonfood commodities, EF sorption rates were generally greater than the 30–40% observed in this study. For example, when EF was treated at LCt99% level for 4 h, sorption of EF was 58% in imported sweet pumpkins [19], 50% in imported bananas [30], and 80% in imported rectangular lumber [9]. Low sorption rates in rubber plants and marble suggest that a greater quantity of rubber plants (e.g., more than 5% w/v loading ratio) or marble (e.g., more than 70% w/v loading ratio) could be treated under commercial settings or a lower dose of EF could be used, which may be especially important when there are negative impacts of EF on the quality of treated commodities.

3.2. Commercial-Scale Trials and Effects of EF Treatment on Quality

3.2.1. Rubber Trees

Complete control of R. speratus workers was achieved in the commercial scale trials (7.2 m3) with 35 g/m3 of EF held for 4 h at 15 ± 1 °C with a 9% loading ratio (w/v) on two species of potted rubber plants. The Ct product of EF was 84.70 ± 0.5 g h/m3, which was greater than the EF LCt99% value for R. speratus at >15 °C (LCt99% = 77.24 g h/m3) [9]. Using the liquid EF vaporizer and nitrogen gas as propellent appeared to effectively deliver EF gas into the fumigation tent. The concentrations of EF were evenly distributed among three different parts inside the fumigation tent (Table 1).
Quality assessment conducted 30 d post fumigation treatment showed that there were no significant differences in leaf chlorophyll contents, leaf hue values, or overall plant injury (i.e., dropped leaves or leaf browning/curling/shriveling) between the EF-treated and untreated rubber plants (Table 2).
Previous studies have shown that EF was an effective fumigant for other imported nursery products such as bare-rooted seedlings and potted nursery plants [31]. For example, Kyung et al. showed that EF treatment at 30 g/m3 for 4 h at >16 °C was effective at controlling Pseudococcus longispinus and P. orchidicola infesting Pachira macrocarpa or Syngonium podophyllum plants [31]. As for the imported potted rubber plants in this study, the imported bare-rooted nursery plants also required an extended growth period after fumigation to increase their commercial value. They reported that there were no differences in various measures of quality for nursery plants grown from bare-rooted plants with or without EF treatment [31]. Thus, EF treatment appears to be a viable MB alternative treatment option for these types of imported nursery products, both in terms of efficacy on the target pests and lack of phytotoxicity. EF is not free of risk of phytotoxicity, and its phytotoxicity on fresh produce or plants appears to depend on the used EF dose (i.e., the higher the dose is, the more the damage), or the treated plant species or variety [31]. In this study, at the tested EF dose, there was no leaf drop, obvious leaf damage, or plant die back after EF treatment. Although the majority of imported rubber plants in Korea are imported with several young leaves, a small fraction of rubber plants are imported with fully grown leaves, which are intended to be sold right after fumigation (personal comm. with nursery plant importers in Korea). Further research is necessary to confirm the effectiveness of EF as a safe fumigant for these types of imported rubber plants.

3.2.2. Stone Products

Complete control of R. speratus workers was also achieved in the commercial-scale trials (33.6 m3) with 35 g/m3 EF held for 4 h at 15 ± 2 °C with a 60% loading ratio (v/v) of imported marble (2 pieces, 10.5 m3/piece). This was expected, as the Ct product of EF from the marble fumigation trial was 263.58 ± 10.9 g h/m3, which was much higher than the 77.24 g h/m3 necessary for 99% mortality of R. speratus at >15 °C [9]. As in our rubber plant fumigation trials, the concentrations of EF in three different parts inside the fumigation tent were uniformly distributed (Table 3). There was no obvious difference in the visual quality of marbles with or without EF treatment.
The Ct product value of 263.58 g h/m3 from the marble fumigation trial appeared to be much greater than what was expected from 35 g/m3 EF treatment for 4 h: on the basis of previous information, the maximal Ct product should be around 140 g h/m3 with minimal sorption and gas leak. This may have been due to the low EF sorption in marble. In this study, the actual amount of EF injected into the tarpaulin tent was 1.17 kg based on the EF dose of 35 g/m3 in 33.6 m3 tent. Considering the volume of loaded marble (21 m3) inside the tent, the actual EF dose could be considered to be 1.17 kg/12.6 m3 if marble was completely impermeable to EF gas. This translates to 90 g/m3 dose of EF (for 4 h), which could result in a Ct product of 360 g h/m3 with zero sorption and leakage. Thus, with 30% EF sorption, as observed from the marble sorption study, the Ct product of 263.58 g h/m3 observed in the scale-up study seems possible. This result suggests that an even greater loading ratio for marble (greater than 60% v/v) could be opted during commercial-scale EF fumigation when other logistics do not limit the use of higher loading ratio.
In this study, the complete control of R. speratus workers was achieved with 4 h fumigation of EF at 35 g/m3 at 15 °C, which is a much shorter fumigation treatment than the currently recommended 24 h fumigation using MB (T500-15) [3]. This difference may not have been due to the greater effectiveness of EF than that of MB for ants and termites [9], but due to the fact that the current provisional MB guideline targets a wide range of nonfood commodities (T500-15) [3]. Thus, our results suggest that (1) a specific EF or MB treatment that targets a specific commodity may be more beneficial in terms of optimizing treatment time, cost, and potential negative impacts on quality than a treatment that targets a broad array of different commodities [18]; and (2) MB treatment may also effectively disinfest ants and termites on nonfood commodities with 4 h of fumigation if optimized for a specific commodity.
Commercial-scale trials targeting S. invicta were not conducted in this study due to regulatory limitations on using invasive pests imposed by Animal and Plant Quarantine Agency in Korea. However, as shown previously, workers of S. invicta are significantly more susceptible to EF than workers of R. speratus are, with Ω LCt99% of S. invicta and R. speratus at 39.88 and 57.03 g h/m3, respectively, with EF fumigation conducted for 1 h at 13 °C [8,9].

4. Conclusions

In conclusion, our results suggest that EF has potential as an MB alternative to control exotic ants and termites, especially S. invicta, on imported rubber plants and stone products with a much shorter, 4 h, fumigation treatment compared to currently recommend 24 h MB treatment. To develop this as a commercial application, future efforts will include confirmatory trials using S. invicta on imported rubber plants and marble products, and a follow-up with International Plant Protection Convention (IPPC) recommendations to review the technical feasibility of the EF treatment as an MB alternative for imported rubber plants and stone products.

Author Contributions

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

Funding

This work was partly supported by funding from the Animal and Plant Quarantine Agency in Korea to B.-H.L. (#PQ 20213B050-SP) and to D.H.C. (#58-2040-0-005-F).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Acknowledgments

We thank the Dong-A Fumigation Co. in the port of Pusan, and Sejong Trade Co., Nursery Plant Importer in the port of Incheon. We also thank the Institute of Quality and Safety Evaluation of Agricultural Products in Kyungpook National University. Opinions, findings, conclusions, and recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the USDA. USDA is an equal opportunity provider and employer.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 12 06066 g001 550
Figure 1. Concentration loss of ethyl formate (EF) (C/C0) in 0.275 m3 fumigation chamber with 5% loading ratio (w/v) of potted imported rubber plants (Fiscus retusa and F. benghalensis). EF was treated at 35 g/m3 for 4 h at 15 °C C = EF concentration determined at one of the time intervals and C0 = EF concentration at 0.1 h. EF concentration was determined at 0.1, 1.0, 2.0, and 4.0 h after EF had been applied to the fumigation chamber.
Figure 1. Concentration loss of ethyl formate (EF) (C/C0) in 0.275 m3 fumigation chamber with 5% loading ratio (w/v) of potted imported rubber plants (Fiscus retusa and F. benghalensis). EF was treated at 35 g/m3 for 4 h at 15 °C C = EF concentration determined at one of the time intervals and C0 = EF concentration at 0.1 h. EF concentration was determined at 0.1, 1.0, 2.0, and 4.0 h after EF had been applied to the fumigation chamber.
Applsci 12 06066 g001
Applsci 12 06066 g002 550
Figure 2. Concentration loss of ethyl formate (EF) (C/C0) in 6.8 L glass fumigation chamber with 70% loading ratio (w/v) of imported marble. EF was treated at 35, 53, and 70 g/m3 for 4 h at 15 °C C = EF concentration determined at one of the time intervals and C0 = EF concentration at 0.1 h. EF concentration was determined at 0.1, 1.0, 2.0, and 4.0 h after EF had been applied to the fumigation chamber.
Figure 2. Concentration loss of ethyl formate (EF) (C/C0) in 6.8 L glass fumigation chamber with 70% loading ratio (w/v) of imported marble. EF was treated at 35, 53, and 70 g/m3 for 4 h at 15 °C C = EF concentration determined at one of the time intervals and C0 = EF concentration at 0.1 h. EF concentration was determined at 0.1, 1.0, 2.0, and 4.0 h after EF had been applied to the fumigation chamber.
Applsci 12 06066 g002
Table
Table 1. Concentration × time (Ct) products (g h/m3) of and the mortality of Reticulitermes speratus workers from 35 g/m3 EF fumigation at 15 ± 1 °C for 4 h treated on imported potted rubber plants (Fiscus retusa and F. benghalensis) in commercial-scale fumigation trials conducted in a 7.2 m3 PVC-tarpaulin tent.
Table 1. Concentration × time (Ct) products (g h/m3) of and the mortality of Reticulitermes speratus workers from 35 g/m3 EF fumigation at 15 ± 1 °C for 4 h treated on imported potted rubber plants (Fiscus retusa and F. benghalensis) in commercial-scale fumigation trials conducted in a 7.2 m3 PVC-tarpaulin tent.
Applied Dose (g/m3)EF Sampling Location Inside TentCt Products (g h/m3)No. of R. speratus Workers TestedNo. of R. speratus Workers DeadMortality of R. speratus Workers (%)
Untreated control--72000
35Front85.8899899100
Middle83.9741741100
Rear84.4750750100
Table
Table 2. Effect of ethyl formate (EF) fumigation (35 g/m3 for 4 h at 15 ± 1 °C) on leaf chlorophyll content, leaf hue value, and overall plant injury of two species of imported potted rubber plants (Fiscus retusa and F. benghalensis) after 30-day postfumigation growth period in a greenhouse. Different letters on means indicate significant differences between EF treatment and untreated control by t-test at p < 0.05.
Table 2. Effect of ethyl formate (EF) fumigation (35 g/m3 for 4 h at 15 ± 1 °C) on leaf chlorophyll content, leaf hue value, and overall plant injury of two species of imported potted rubber plants (Fiscus retusa and F. benghalensis) after 30-day postfumigation growth period in a greenhouse. Different letters on means indicate significant differences between EF treatment and untreated control by t-test at p < 0.05.
Nursery PlantsCt Products
(g h/m3)		Chlorophyll Content (Mean ± SE)Hue Value (Mean ± SE)Overall Injury
Untreated ControlEF TreatedUntreated ControlEF Treated
F. retusa84.70 ± 0.560.12 ± 1.51 a61.51 ± 2.15 a17.66 ± 1.56 a17.50 ± 0.91 a0
F. benghalensis61.39 ± 1.20 a59.33 ± 2.49 a18.19 ± 2.03 a18.44 ± 1.69 a0
Table
Table 3. Concentration × time (Ct) products (g h/m3) of and the mortality of Reticulitermes speratus workers from 35 g/m3 EF fumigation at 15 ± 1 °C for 4 h treated on imported marble in commercial-scale fumigation trials conducted in a 33.6 m3 tarpaulin tent.
Table 3. Concentration × time (Ct) products (g h/m3) of and the mortality of Reticulitermes speratus workers from 35 g/m3 EF fumigation at 15 ± 1 °C for 4 h treated on imported marble in commercial-scale fumigation trials conducted in a 33.6 m3 tarpaulin tent.
Applied Dose (g/m3)EF Sampling Location Inside TentCt Products
(g h/m3)		No. of R. speratus Workers TestedNo. of R. speratus Workers DeadMortality of R. speratus Workers (%)
Untreated control--66100
35Front279.87691691100
Middle267.93606606100
Rear242.94687687100
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Kim, D.; Kwon, T.H.; Park, M.-G.; Kim, K.W.; Cha, D.H.; Lee, B.-H. Ethyl Formate-Based Quarantine Treatment for Exotic Ants and Termites in Imported Rubber Plants and Stone Products. Appl. Sci. 2022, 12, 6066. https://doi.org/10.3390/app12126066

AMA Style

Kim D, Kwon TH, Park M-G, Kim KW, Cha DH, Lee B-H. Ethyl Formate-Based Quarantine Treatment for Exotic Ants and Termites in Imported Rubber Plants and Stone Products. Applied Sciences. 2022; 12(12):6066. https://doi.org/10.3390/app12126066

Chicago/Turabian Style

Kim, Dongbin, Tae Hyung Kwon, Min-Goo Park, Kyung Won Kim, Dong H. Cha, and Byung-Ho Lee. 2022. "Ethyl Formate-Based Quarantine Treatment for Exotic Ants and Termites in Imported Rubber Plants and Stone Products" Applied Sciences 12, no. 12: 6066. https://doi.org/10.3390/app12126066

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