Ethyl formate fumigation as a replacement for methyl bromide fumigation in dried vine fruit.

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2 Ethyl formate fumigation as a replacement for methyl bromide fumigation in dried vine fruit. Dried Fruit Research and Development Council, Project CSH 64D C.R. Tarr 1, R. Reuss 2, P.R.Clingelefer 1, P. Annis 2, 1 CSIRO Plant Industry 2 Stored Grain Research Laboratory Horticulture Unit CSIRO Entomology Private Mail Bag GPO Box 1700 Merbein Vic Canberra ACT 2601 AUSTRALIA AUSTRALIA Ph (03) Fax (03) caroline.tarr@csiro.au Purpose To develop effective and safe methods to fumigate cartons and bulk bins of dried vine fruit with ethyl formate. This includes :- investigation of the penetration efficiency of ethyl formate into large masses of dried vine fruit. exposure to ethyl formate of cultured wild insect populations of major pests to identify effective dosage and identify tolerance compared to unexposed populations. consult with packers re the development of suitable fumigation protocols, develop and demonstrate this technology to industry. Acknowledgement DFRDC $65,776 CSIRO $36,377 Report finalised April 2004 Disclaimer All use of the information in the report shall be entirely at the risk of the recipient. CSIRO and DFRDC, their officers, employees and agents accept no responsibility for any person acting on or relying upon any opinion, advice, representation, statement, or information contained in the report and disclaim all liability for loss, damage, cost or expense incurred or arising by any reason of any person using or relying on the information contained in the report or by reason of any error, omission, defect or mis-statement. 1

3 Table of Contents Media Summary...3 Technical Summary...4 Introduction...5 Methodology...6 Section 1: Investigations into penetration of ethyl formate into unprocessed and processed sultanas...7 Relative Humidity of sultanas...9 Bulk density of sultanas...10 Natural levels of ethyl formate, other volatiles and accumulation of carbon dioxide...12 Fate of ethyl formate applied to sultanas...16 Movement of ethyl formate through columns of sultanas...18 Section 2: Mortality studies of pest populations sourced from Sunraysia to fumigation with ethyl formate and comparisons with an unexposed population to identify any development of tolerance to the fumigant...25 Materials and Methods...25 Results and Discussion...28 Section 3: Ethyl formate fumigation as a replacement for methyl bromide fumigation in dried vine fruit...39 Trial 1. Ethyl formate fumigation of a shipping container load of unprocessed dried sultanas in June Trial 2: A combined ethyl formate and CO 2 fumigation of a shipping container of unprocessed dried sultanas in April Discussion...44 Section 4 : Draft method of application of Ethyl formate (eranol) to shipping containers to fumigate dried vine fruit...45 Technology Transfer...50 Bibliography...50 Recommendations

4 Media Summary Methyl bromide, a scheduled ozone depleter, has been used for fumigation of many food commodities. However, its use is being phased out as part of the international Montreal protocol. This leaves many industries including the dried vine fruit (dvf ) industry with a need to develop alternative treatment strategies. Previous dried vine fruit research has highlighted several alternatives, including the use of ethyl formate as a space fumigant. However, ethyl formate may be explosive under certain conditions and research on dosage levels and application methods for space fumigation needed to be undertaken. This project examined :- the penetration efficiency of ethyl formate into dried vine fruit dosages needed for 100% mortality of dried vine fruit pests in space fumigation whether tolerance to ethyl formate has developed in the Sunraysia insect populations the mechanics of fumigation in large spaces development of a method for fumigation of dvf in a shipping container sized space. There was very little adsorption of ethyl formate by the fruit, a good characteristic for fumigation, but it was found to move slowly through compact dried vine fruit. This slow dispersion was alleviated by including it in a carrier gas of CO 2, a concept developed during the project. Laboratory studies showed dried vine fruit pests were susceptible to dosages of between 20-40gm -3 of ethyl formate. An effective dosage, after allowing for sorption, of 40gm -3 should provide acceptable mortality of dried vine fruit pests. After more than 50 years treatment in the Sunraysia district there was no evidence of tolerance to ethyl formate having developed in pest populations. Two fumigations with ethyl formate were carried out in shipping containers. The first used liquid ethyl formate and demonstrated that this fumigant worked in cold conditions. The second demonstration used CO 2 as a carrier gas, thereby reducing flammability and improving distribution of ethyl formate. These fumigations produced 99.9% and 100% mortality on complete lifecycles of all dried vine fruit pests included. It is proposed that industry consider the potential to adopt ethyl formate as a space fumigant as an alternative to Methyl Bromide. A draft application protocol has been developed to assist industry in giving consideration to this possibility. 3

5 Technical Summary Methyl bromide, a scheduled ozone depleter, is used for fumigation of dried vine fruit (dvf). Its availability for use on products other than for quarantine reasons is being phased out by 2005 as part of the international Montreal protocol. This leaves the dvf industry with a need to replace methyl bromide with alternative treatment strategies. Previous research has highlighted several alternatives including the use of ethyl formate as a space fumigant. Ethyl formate is registered for use in dried fruit in small packages (approx 15kg). It has proven effective on the major insects present in the Australian industry. Research has shown it leaves no discernable residues in the fruit 7 days after treatment. Ethyl formate has a high daily exposure level due to it s low human toxicity (TLV 100 ppm) and may offer a suitable replacement strategy in dried vine fruit for methyl bromide. However, ethyl formate is explosive under certain conditions and research on dosage levels and application methods for space fumigation needed to be undertaken. This project examined :- the penetration efficiency of ethyl formate into dried vine fruit dosages needed for 100% mortality of dvf pests in space fumigation whether tolerance to ethyl formate has developed in the Sunraysia insect populations the mechanics of fumigation in large spaces development of a method for fumigation of dvf in a shipping container sized space. There was very little adsorption of ethyl formate by the fruit when compared to grains, a good characteristic for fumigation (Desmarcheliar, Johnston and Le Trang Vu 1999, Hilton and Banks 1997). However it was found to move slowly through compact dried vine fruit. This slow dispersion was found to be alleviated by including it in a carrier gas of CO 2 a concept application method developed during the project (Allen, S.E., Desmarchelier J.M., 2002). Laboratory toxicity studies showed dvf pests were susceptible to dosages of between 20-40gm -3 of ethyl formate. The same studies showed no evidence of tolerance to ethyl formate having developed in the Sunraysia pest populations. Further research on insect toxicity using the most resistant lifecycle stages of dvf pests should be carried out. An effective dosage after allowing for sorption onto fruit of 40gm -3 should provide acceptable mortality of dvf pests. A draft application protocol is included in this report. Two fumigations with ethyl formate were carried out in shipping containers. The first used liquid ethyl formate and demonstrated that this fumigant will work in cold conditions (average 11 o C) at the lower temperature limit for methyl bromide application. The second demonstration used CO 2 as a carrier gas, thereby reducing flammability and improving distribution of ethyl formate. The first fumigation killed all stages of O. surinamensis and all stages of T. confusum with the exception of 2 pupae from a total of 3000 test insects. The second fumigation produced 100% mortality of the complete lifecycle of T. confusum and pupae, larvae and adults of P. interpunctella as well as O. surinamensis present in the fruit. It is proposed that industry investigate adoption of ethyl formate as a space fumigant. The use of a proprietary CO 2 / ethyl formate gas mix for fumigation should be investigated as this new development will significantly increase the safety of application and make commercial use a reality. 4

6 Introduction The phase out of methyl bromide for use as a fumigant of products other than those requiring fumigation for quarantine reasons is rapidly approaching (2005). This will leave the dried fruit industry with a need for alternative treatment strategies to replace methyl bromide. The final reports from the DFRDC funded project CSH 34 and 44 presented several alternative treatment strategies to replace and reduce the need for methyl bromide fumigation in the control of insect infestations in dried vine fruit. As part of these strategies, the use of ethyl formate as an alternative space fumigant was highlighted as having potential. Ethyl formate is at present registered for use in packaged dried fruit where it is used as an insecticide for the final disinfestation of the product during packaging. It has proven to be effective on the major insects present in the Australian industry (Hilton and Banks 1997, Tarr and Clingeleffer 1993), and leaves no discernable residues in the fruit 7 days after treatment (unpublished internal CSIRO report). Ethyl formate has a high daily exposure level due to it s low human toxicity (TLV 100ppm) and may be suitable as a replacement in dried fruit for methyl bromide when used in combination with other alternative strategies. A report on ethyl formate highlighted its explosive nature at concentrations between % in air, if a source of combustion is provided (Pearson, R.D., Apte, V.B., 1998). However safe application to larger enclosures has been proposed and demonstrations carried out by grain researcher Dr. J. Desmarchelier at CSIRO Entomology, with the application of ethyl formate in water as both a fumigant and surface spray treatment for grain. Desmarchelier demonstrated in initial experimentation that ethyl formate like ethanol is not flammable when mixed with water (Desmarchelier, et al. 1998). The potential application of ethyl formate as a space fumigant leads to questions about its ability to penetrate through large bulks of fruit. Hence, a method of application to bulk sultanas as a fumigant needs to be developed and its effective penetration tested prior to industry recommendations being made. Research is being carried out at CSIRO Entomology into the application of ethyl formate to grains. As a part of this project CSIRO Entomology and Plant Industry investigated its application for dvf. Objectives To develop efficacious and safe application methods for the fumigation of dried vine fruit in large carton or bulk bin stacks using ethyl formate. Investigate the penetration efficiency of ethyl formate into large masses of dried vine fruit, ie. bulk bins, stacks and palletised carton stacks. To consult with packers regarding the development of suitable fumigation protocols, then develop and demonstrate this technology to industry. 5

7 Methodology Laboratory studies were conducted to test the efficacy of ethyl formate penetration into large masses of sultanas, e.g. bulk bins and palletised cartons. The studies were carried out on both processed and unprocessed fruit. The penetration of ethyl formate was measured using a column of fruit to simulate bulk dried fruit. This was carried out at CSIRO Entomology s, Stored Grain Laboratory in Canberra. See section 1 for more detail. An insect population, obtained from the Sunraysia district, was cultured until large enough populations were raised for use in laboratory mortality trials and experimental space fumigation treatments with ethyl formate. Insects were trapped during the autumn of 1999 and cultured to obtain sufficient numbers by spring of The major pests Plodia interpunctella, Oryzaephilus surinamensis and O. mercator were cultured, plus other pests where enough adults were captured to establish a viable population. These cultures were used to prove the efficacy of the fumigant on local insect populations and to pinpoint resistance (tolerance) which may have developed in local populations. See section 2 for more detail. Application methodologies for fumigation were developed and demonstrations of fumigation methods using ethyl formate in shipping containers were scheduled. The methods demonstrated the use of ethyl formate in a larger space equivalent to a fumigation tent and was timed to occur during the peak infestation periods of the season where possible. These methods took advantage of natural infestations for the demonstration of efficacy as well as cultured bioassays. See section 3. A draft application protocol was developed for the dried vine fruit industry. See section 4. 6

8 Section 1: Investigations into penetration of ethyl formate into unprocessed and processed sultanas Measurement of ethyl formate by gas chromatography Background Two different instruments and three different columns were used to separate headspace containing ethyl formate, ethanol and a variety of other compounds. Results and conclusions The Shimadzu GC 6AM fitted with a SP 2401/SE 30 glass column rapidly detected high levels of ethyl formate. Other compounds, such as ethanol, methanol and methyl formate could not be separated with this instrument. While the Shimadzu may be suited for measuring fumigation levels of ethyl formate in the absence of ethanol it is unsuited for low levels of the gas and in applications that contain other esters or alcohols. The Varian 3600 fitted with a 30 m DB-FFAP column can separate ethyl formate from ethanol and to some extent from the other components. However, identification of peaks by retention times is not easily achievable, as all peaks are eluted in less than two minutes. The column has some application where there is ethyl formate and Ethanol contained in samples but no (or very little) other esters and alcohols are present. Separation of ethyl formate and other esters, alcohols, ketones and aldehydes was best achieved with a 60 m AT-WAX column. Series of formates and alcohols were separated to the baseline (Figures 1.1 and 1.2). At 80 C compounds relevant to the ethyl formate work could be separated in less than 8 minutes. Separation was further improved by lowering oven temperature. At 125ºC analysis can be carried out in less than 5 minutes, with adequate separation of the most relevant compounds. The AT- WAX column is considered to be the column of choice for ethyl formate work. It is especially suitable for natural levels of ethyl formate and other compounds, studies on sorption and decay of the fumigant and any other application where methyl formate, methanol and ethanol as well as other compounds need to be separated from ethyl formate. 7

9 Figure 1.1. Separation of ester series (formates) Figure 1.2. Separation of alcohol series 8

10 Relative Humidity of sultanas Background Moisture content of sultanas is determined by methods different to those commonly used for the moisture contents determination in grain at the SGRL. Present and future work in this area requires the use of these techniques to determine one of the vital parameters in sultana storage and for developing fumigant treatments for dried fruit. Methods Processed and unprocessed sultanas were sealed in 250 ml glass jars with a lid modified to allow relative humidity (rh) measurement with an electronic rh meter (accuracy ±1%, RS Relative Humidity Meter, calibrated with lithium chloride solution standard). The sultanas were then stored at four temperatures and rh was measured after a minimum of 24 hours of equilibration. The moisture content of the sultanas was estimated from a published isotherm (Figure 1.3). 25 moisture content % y = 100x 2-70x water activity Figure 1.3. Sultana isotherm. Source: Pixton and Warburton Results Processed sultanas had a higher water activity than unprocessed fruit (Figure 1.4). Increases in rh with storage temperature followed a linear relationship. The estimated moisture content of sultanas is shown in Table

11 Unprocessed sultanas Processed sultanas rh % Storage temperature C Figure 1.4. Relative humidity of storage environment for sultanas stored at different temperatures Table 1.1. Measured rh and estimated moisture contents of sultanas Commodity Temperature ºC RH % Estimated moisture contents % Processed Unprocessed Bulk density of sultanas Background The compressibility of sultanas could play an important role in the way ethyl formate moves through a column of dried fruit. Methods The bulk density of unprocessed and processed sultanas was measured with a bulk density balance (manufactured by CBH). Processed and unprocessed sultanas were compressed by impact 20 times. After each compression, the bulk density was determined. Results Unprocessed sultanas had considerably less bulk density than processed sultanas (Table 1.2). Even after 20 impact compressions the bulk density of the commodity was still increasing slightly (Figure 1.5). Expressed as a percentage, bulk density increase by compression was more substantial in unprocessed compared to processed fruit (Figure 1.6). By avoiding compression of unprocessed 10

12 sultanas it should be possible to increase the ease of fumigant penetration through interstitial spaces into the bulk and to insure a more even distribution of fumigant. Table 1.2. Bulk density of processed and unprocessed sultanas. Type uncompressed (kg/hl) compressed (*5) (kg/hl) unprocessed Average processed Average unprocessed processed Bulk density (kg/hl) Number of compressions Figure 1.5. Increases in bulk density (kg/hl) of processed and unprocessed sultanas as a result of progressive manual compression 11

13 unprocessed processed Increase in bulk density % Number of compressions Figure 1.6. Increases in bulk density (%) of processed and unprocessed sultanas as a result of progressive manual compression Natural levels of ethyl formate, other volatiles and accumulation of carbon dioxide Background Measurement of respiratory gases gives an estimate of biochemical activity in stored products. In turn, this influences the interaction between product and fumigant. Natural levels of fumigants and their products may occur in storage atmospheres. Information on biochemical reactions occurring in the untreated product forms part of developing an understanding of the fumigation process, quality changes and the likelihood of significant fumigant residues. As carbon dioxide is a likely end product of ethyl formate breakdown it is important to develop knowledge of the amount of gas produced by untreated sultanas. Materials and Methods Processed and unprocessed sultanas were sealed in flasks and stored at 25, 35, and 45 C. Ethyl formate and related compounds as well as CO 2, O 2 and CO were monitored over several weeks. Analysis of alcohols and esters Analysis of gas samples was carried out using a Varian 3600 CX GC with an AT-WAX column (60 m 0.53 mm ID 1.0 µm) and a FID. Chromatographic conditions used: carrier gas helium, pressure 6.5 psi, oven temperature 80ºC, detector temperature 275ºC, injector temperature 150ºC. Injection volume was 10 µl delivered with a gastight syringe. Peaks were identified by comparison to standard injections. Concentrations were calculated on the basis of peak areas from regression equations calculated from standards of various dilutions. Analysis of CO 2, O 2 and CO Analysis of gas samples was carried out using a Fisher model 1200 Gas Partitioner with mesh Columpak PQ (6.5 ft x 1/8 in) and mesh Molecular Sieve 13X (11 ft by 3/16 in) columns in series and a Thermal Conductivity Detector. Chromatographic conditions used: carrier gas, helium with a flow rate of 30 ml/min and oven temperature 50 C. Injection volume was 1 ml delivered with 12

14 a gastight syringe. CO 2 and O 2 concentrations were calculated based on adjusted peak areas. Peak areas were calibrated periodically using a standard gas mixture with known CO 2, O 2, CO and N 2 composition. The limit of detection for CO 2 was below atmospheric concentrations. Results and discussion CO 2, O 2 and CO Accumulation of CO 2 and loss of O 2 was temperature dependent and followed trends commonly seen in stored grain (Figures 1.7. and 1.8.). CO also accumulated in a manner similar to canola (Figure 1.9.). For all gases changes were more pronounced in the unprocessed sultanas. Unprocessed sultanas had a higher rh than processed fruit (about 2% higher) but this does not completely account for the differences. RQ increased with increasing storage temperature and was considerably below unity at lower storage temperatures (Table 1.3.). This suggested that respiration of carbohydrates was not the primary source of changes in carbon dioxide and oxygen. The source of CO accumulation should be investigated, but it can be assumed that the considerable levels of this gas measured are an indicator of ongoing oxidation reactions. The comparatively high impact of stored sultanas on storage atmospheres suggests a high level of oxidative activity in the product. The impact of this phenomenon on ethyl formate breakdown needs to be investigated in more detail. Unprocessed 25 C Processed 25 C Unprocessed 35 C Processed 35 C Unprocessed 45 C Processed 45 C CO2 % v/v storage time (weeks) Figure 1.7. Changes in carbon dioxide concentrations in hermetically sealed sultanas 13

15 Unprocessed 25 C Processed 25 C Unprocessed 35 C Processed 35 C Unprocessed 45 C Processed 45 C O2 % v/v storage time (weeks) Figure 1.8. Oxygen consumption of hermetically sealed sultanas CO ppm v/v Unprocessed 25 C Processed 25 C Unprocessed 35 C Processed 35 C Unprocessed 45 C Processed 45 C Storage time (weeks) Figure Carbon monoxide production of hermetically sealed sultanas Table 1.3. Respiratory quotients (RQ) of sultanas after 5 weeks of storage Temperature C Material RQ after 5 weeks 25 Processed 0.3 Unprocessed Processed 0.6 Unprocessed Processed 0.7 Unprocessed

16 Volatile compounds The alcohols methanol and ethanol were present in higher concentrations than methyl and ethyl formate (Table 1.4.). Ethanol predominated at 25 and 35ºC but high levels of methanol were found at 45ºC. No clear trend for higher levels of these compounds in processed compared to unprocessed produce was apparent. On average, the levels of ethyl formate and the alcohols increased with increasing storage temperature. In processed sultanas methyl formate levels peaked after 3 weeks of storage at 25 and 35ºC. High levels were found after 1 week of storage at 45ºC, in processed as well as unprocessed sultanas. On average, more methyl formate was found in processed sultanas compared to unprocessed fruit. Ethyl formate levels seemed to be temperature dependent in processed sultanas, a trend that was less clear in unprocessed fruit. Methanol levels were almost always highest at 45ºC in processed and unprocessed sultanas. Concentrations peaked after 3 weeks storage. In contrast, ethanol concentrations in processed sultanas were lower with increasing storage temperature. However, there were high concentrations of ethanol in the headspace of unprocessed sultanas stored at 45ºC for 1 week. Table 1.4. Alcohol and esters levels in the headspace of sealed flasks containing sultanas. Figures are averages of measurements taken over 5 weeks. (MeF = methyl formate, Etf = ethyl formate, MeOH = methanol, EtOH = ethanol ) Temperature C Commodity MeF mg/l EtF mg/l MeOH mg/l EtOH mg/l 25 processed unprocessed average processed unprocessed average processed unprocessed average The emerging profile of volatile alcohols and esters in sultanas provides an interesting challenge for the analysis of low levels of ethyl formate on sultanas. Chromatographic separation of alcohols from ethyl formate is crucial to achieving realistic estimates of residual fumigant post fumigation. At 25 and 35ºC, natural levels of ethyl formate were far below levels considered safe for consumption (less than 0.3 mg/l). At 45ºC levels were about half of the safe level. This is unlikely to be due to previous treatments as the unprocessed sultanas had similar levels of organic ethyl formate. 15

17 Fate of ethyl formate applied to sultanas Background Understanding the breakdown or sorption of ethyl formate on dried fruit is crucial in developing fumigation techniques and understanding the risk of fumigant residues. Ethyl formate applied as liquid or vapour Materials and methods 120 g of processed fruit was sealed in flasks and ethyl formate was applied directly onto fruit (liquid) or onto a filter paper in the flask s neck (vapour). Results Ethyl formate breakdown occurred quite rapidly. However, the fumigant was quite persistent in comparison with the rates of loss experienced when the fumigant is applied to cereal commodities such as rice and wheat. It may be that this fact is what makes ethyl formate particularly suited as a treatment for dried fruit. There were no substantial differences due to the method of application (Figure 1.10.), that is applying the fumigant directly to the commodity did not increase loss of vapour. From a sorption perspective there would be little advantage in vaporising the fumigant before application. applied as liquid applied as gas EtF ppm v/v Exposure (hours) Figure Loss of ethyl formate(etf) applied as gas or liquid to processed sultanas 16

18 Processed and unprocessed sultanas Materials and methods 250 g of processed and unprocessed sultanas were sealed in 500 ml flasks and dosed with 100 µl of ethyl formate. Headspace was monitored with Varian GC and AT-WAX column as described. Results Little ethyl formate was lost during the early stages of fumigation (Table 1.5.). Over 24 hours approximately half the fumigant was lost. There was no difference between unprocessed and processed fruit. Loss of fumigant can be estimated by a regression (Figure 1.11). The vapour of ethyl formate applied to fruit is persistent compared to application to cereal commodities. Consequently, some benefit may be derived by applying ethyl formate as a space type of fumigant to processed or unprocessed dried fruit stored in sealed containers. Further investigations are necessary to explore this aspect of dried fruit/ethyl formate interactions, paying particular attention to filling ratios, temperature and water activity and their effect on the persistence of ethyl formate vapour. Table 1.5. Percentage loss of ethyl formate in processed and unprocessed fruit over a 24 h period. Ethyl formate loss % Exposure Time Minimum Maximum Average Processed Unprocessed EtF mg/empty flask y = x R 2 = Exposure (hours) Figure Loss of ethyl formate (EtF) from flasks containing processed and unprocessed sultanas 17

19 Movement of ethyl formate through columns of sultanas Ethyl formate (eranol) applied to surface of processed and unprocessed fruit in small glass columns Background To investigate the way ethyl formate penetrates through sultanas glass columns were tightly packed with processed and unprocessed fruit. To differentiate between vapour and combined vapour-liquid movement of fumigant ethyl formate was applied to a layer of glass beads (vapour) or directly to the fruit (vapour-liquid). Materials and methods Glass columns (ID 30mm, length 450 mm) with four sample ports (headspace, 50 mm, 160 mm, 270 mm) were filled with 60 g of glass beads followed by 120 g of processed or unprocessed sultanas. Eranol was then applied either to the surface of the fruit or on top of a 20 g layer of glass beads. The dose was 50 µl of ethyl formate (equivalent to 0.42 ml/kg, within lower range of label). Results The majority of ethyl formate vapour remained in the headspace of the column for both methods of application and types of commodities (Figures and 1.13.). Some penetration occurred at all levels of the column with the highest concentration at the distance closest to the point of application. Direct application led to higher headspace concentrations than application to glass beads. Ethyl formate vapour appeared to penetrate processed sultanas better than unprocessed sultanas. However the liquid-gas ethyl formate penetrated columns of both processed and unprocessed fruit more successfully, possibly by liquid seepage through interstitial spaces and a wick effect of sultanas exposed to high levels of liquid fumigant. From this data it appears that fumigant does not easily penetrate tightly packed columns of sultanas and that ethyl formate vapour does not penetrate as successfully as liquid-vapour mixtures occurring during direct application of the fumigant. Figure Movement of ethyl formate through columns of sultanas. Ethyl formate was applied to a layer of glass beads at 0.42 ml/kg (equivalent to 10 ml/25kg). Column contained 120 g of sultanas. Two replicates are shown. Numbers are averages of measurements taken over a 24 hour period. 18

20 Figure Movement of ethyl formate through columns of sultanas. Ethyl formate was applied directly to fruit at 0.42 ml/kg (equivalent to 10 ml/25kg). Column contained 120 g of sultanas. Two replicates are shown. Numbers are averages of measurements taken over a 24 hour period. Ethyl formate (eranol) applied at different depths of a column containing processed sultanas Background To further investigate the way ethyl formate penetrates through sultanas, glass columns were tightly packed with processed and unprocessed fruit and fumigant was applied at different depth. Materials and methods Glass columns (ID 30mm, length 450 mm) with four sample ports (headspace, 50 mm, 160 mm, 270 mm) were filled with 120 g of processed or unprocessed sultanas. Eranol was then applied at four different depths. The dose was 50 µl of ethyl formate (equivalent to 0.42 ml/kg, within lower range of label). Results When fumigant was applied to the surface most of the material remained in the headspace with some penetration 50 mm into the column. (Figure 1.14). When ethyl formate was applied 50 mm into the column a more even distribution of fumigant was found (Figure 1.15). Further into the column distribution was skewed towards the bottom of the column (Figures 1.16 and 1.17). There appears to be a clear advantage to applying the fumigant below the surface of the fruit to achieve a more even distribution of the chemical. However, a gradient skewed towards the top of the column will result. Application towards the centre to bottom of the column leads to a bottom heavy distribution. Clearly simultaneous application at several depths would be the ideal way to achieve even fumigant distribution. 19

21 EtF mg/l Exposure time (hours) Figure Penetration of ethyl formate through a column of sultanas. Fumigant applied directly to surface. Legend shows sample depth in mm EtF mg/l Exposure time (hours) Figure Penetration of ethyl formate through a column of sultanas. Fumigant applied 50 mm from surface. Legend shows sample depth in mm. 20

22 EtF mg/l Exposure time (hours) Figure Penetration of ethyl formate through a column of sultanas. Fumigant applied 160 mm from surface. Legend shows sample depth in mm EtF ppm v/v Exposure time (hours) Figure Penetration of ethyl formate through a column of sultanas. Fumigant applied 270 mm from surface. Legend shows sample depth in mm. 21

23 Ethyl formate movement through 85 mm columns of unprocessed and processed sultanas Background Large PVC columns were filled with processed and unprocessed fruit. To investigate upward and downward movement of vapour, fumigant was applied to the centre of the column. Materials and methods Four PVC columns (ID 85 mm, length 1 m, half-hole septa sample point every 50 mm) were loosely filled with 2.5 kg of unprocessed sultanas or 3.5 kg of processed sultanas to leave a headspace of 180 mm. Ethyl formate in the form of Eranol was applied according to label to the centre of the compressed column (injection point). Measurements were then taken at various distances above and below the injection point. Analysis was carried out using Varian GC with AT-WAX column as described previously, except that oven temperature was increased to 100ºC to shorten retention times. Results Distribution of ethyl formate vapour through a column of unprocessed fruit was much more even than through the processed commodity (Figures 1.18 and 1.19). Higher levels were found below the application point, probably due to the effect of gravity. Application of ethyl formate to the centre of a loosely packed column of unprocessed fruit seems to achieve a good distribution of the fumigant. It is likely that the greater ease of penetration of liquid and vapour ethyl formate through the less dense unprocessed fruit accounts for this effect. 180 Ethyl Formate mg/l Distance from application (mm) Figure Penetration of ethyl formate through a column of processed sultanas 6 h after application. Negative numbers show distance below application point, positive numbers show distances above application point. 22

24 Ethyl Formate mg/l Distance from application (mm) Figure Penetration of ethyl formate through a column of unprocessed sultanas 6 h after application. Negative number show distance below application point, positive numbers show distances above application point. Effect of compression on movement of ethyl formate through 85 mm columns of unprocessed sultanas Background Compression seems to play an important part in the penetration and distribution of ethyl formate liquid and vapour. To investigate this effect in unprocessed sultanas, columns were manually compressed to simulate compaction. Materials and methods Four PVC columns (ID 85 mm, length 1 m, half-hole septa sample point every 50 mm) loosely filled with approximately 2.5 kg of unprocessed sultanas to leave a headspace of 180 mm. Column 1 remained non-compressed. Columns 2, 3 and 4 were compressed by 50, 100 and 150 mm respectively. Ethyl formate in the form of Eranol was applied according to label to the centre of the compressed column (injection point). Measurements were then taken at 100, 200 and 300 mm distance above and below the injection point. Analysis was carried out using Varian GC with AT- WAX column as described previously, except that oven temperature was increased to 100ºC. Results After 3 hours of fumigation the majority of fumigant was found at or below the point of application (Figure 1.20). There was no clear relationship between compression and fumigant distribution. However, after 24 hours high levels of ethyl formate were associated with low compression of sultanas (Figure 1.21). In particular this was clear at the point of application and at the points furthest away from application. It seems that compression plays no or only a minor role during the early stages of fumigation but has an impact on fumigant distribution in the longer term. Further 23

25 investigations with detailed sampling at various stages during the fumigation are necessary. Toxicological data on necessary times of exposure to ethyl formate in sealed systems is needed to guide these experiments Compression (mm) mm -200 mm -300 mm Distance from injection point Figure Ethyl formate measured in compressed columns of unprocessed sultanas 3 h after application. Data shown as 3-D cone graph. Height of cone shows ethyl formate concentration Compression (mm) mm -200 mm -300 mm Distance from injection point Figure Ethyl formate measured in compressed columns of unprocessed sultanas 24 h after application. Data shown as 3-D cone graph. Height of cone shows ethyl formate concentration. 24

26 Section 2: Mortality studies of pest populations sourced from Sunraysia to fumigation with ethyl formate and comparisons with an unexposed population to identify any development of tolerance to the fumigant. Background Insect populations obtained from the Sunraysia district, were raised and subjected to space fumigation treatments with ethyl formate. Insects were trapped during the autumn of 1999, several cultures were started at this time to obtain sufficient numbers by the spring of The major pests Plodia interpunctella, Oryzaephilus surinamensis and O. mercator were targeted, other species which were captured in abundance were also cultured. These included Tribolium confusum, Tribolium castaneum (Herbst) and Ephestia figulilella. Insect cultures after multiplication were transported to CSIRO in Canberra for mortality studies. The aim of this research was to prove the efficacy of the fumigant on local insect populations and pinpoint any resistance (tolerance) to ethyl formate which may have developed in local populations. It included: establishing whether the local Sunraysia pest populations had developed tolerance to ethyl formate fumigation. This was carried out by establishing a range of dosages which caused a range of mortalities for insect populations from Sunraysia (eg. 0, 50, 90, 99, and 100% mortality) and then comparing these results with results from cultures raised in Canberra which had no history of ethyl formate exposure. establishing dosage parameters to obtain 95 and 100% kill on local Sunraysia and Canberra populations. CSIRO Entomology (SGRL) background research has shown that ethyl formate is sorbed rapidly onto many grains and onto sultanas although at a much lower rate (section 1). This means that a dosage observed to kill insects exposed without sultanas present will be the dosage that needs to reach the insects in the fruit after sorption has been taken into account. At present sorption has not been studied in sufficient detail to know how much fumigant will be sorbed in every scenario. It was decided that at this stage mortality studies without fruit would be of more use than mortality studies with fruit present. Materials and Methods Bioassay methods Cultures of local insect populations were established by collecting insects from Sunraysia dried vine fruit packing establishments during the 1999 season and breeding up populations of these insects. The major pest species present were identified under an Olympus stereo zoom microscope and placed in incubation containers with their favoured food substrate. Insects were cultured at 25 o C in an incubation chamber under a 14 hour daylight - 10 hours dark regime. The chamber had no humidity controller and this was modified slightly by the addition of steam from a steam humidifier ( Eucybear brand ). The insects captured and cultured included, the beetles, Oryzaephilus surinamensis (common name sawtoothed grain beetle), Tribolium confusum (common name confused flour beetle), Tribolium castaneum (common name red flour beetle), Oryzaephilus mercator (common name merchant grain 25

27 beetle), the moths Plodia interpunctella (common name Indianmeal moth) and Ephestia figulilella (common name raisin moth). The Tribolium species were raised on a mixture of wholemeal stone ground flour, unprocessed sultanas and yeast. The rest of the insects were raised on unprocessed sultanas. All food substrates were frozen for 3 months prior to use to eliminate mite infestation and cross infestation of the cultures. Prior to use in the dosage trials insects were separated from the food substrate, either by sieving, running adults off the food or hand selecting the desired life cycle stage. After exposure to the fumigant a recovery time of 24 hours was allowed prior to estimating mortalities. During this period insects were kept at 25 o C on suitable food substrate in controlled temperature rooms. Fumigation methodology Insect lifecycle stages were separated from food substrate and other life cycle stages and placed in 150 ml glass jars with Bakelite lids. Ventilation was through mesh incorporated into the lid. The jars were placed in glass vacuum desiccators and exposed to a predetermined concentration of ethyl formate for 24 hours at 25 o C. Gas dosage was calculated using gas laws and applied to a liquid. In this case Ethyl formate dose (ml) = required Concentration (mg/l) x Volume of container (l) liquid density(g/l) the volume of the desiccators had been measured gravimetrically prior to the experiment by measuring the volume of water held by the sealed desiccator. In this case the Volume of the container (l) = weight of water at 25 o C x weight of water (g) (cc to ml) The weight of water at 25 o C is found in standard tables, supplied by SGRL (fumigant handling and measurement booklet pg 122). The liquid density of ethyl formate (eranol) was taken from the manufacturers specifications; for eranol this was 901 g/l. The addition of a gas (or liquid, which becomes a gas) to a sealed desiccator increases the pressure inside the desiccator. To make allowances for this the volume the gas will occupy in the desiccator is removed prior to addition. The volume to be removed is calculated using gas laws. Based on the general gas law PV = nrt The dosage of the fumigant in mls (for a gas) and hence the amount removed from the desiccator can be calculated either using the gas density or the volume of 1 mole: Dosage (ml) = C x V x 1/ gas density x T / T GD x P GD / P Or Dosage (ml) = C x V x Volume of 1 mole / molecular weight x T / Tmol x Pmol / P, 26

28 Where gas density (g/l) and volume of 1 mole (l) are found in tables, C = required concentration, mg/l V = volume, (L) T = Lab temperature, o K P = Lab pressure, mb T GD = temperature for gas density, o K P GD = pressure for gas density, mb Tmol = temperature for 1 mole, o K P mol = pressure for 1 mole, mb In this experiment we used the volume of 1 mole Pressure and temperature were measured every day prior to fumigation. eg. Gas removed (ml) = C x V x (v of 1 mole) / (mol wt) x 296.7/ 293 (t/tmol) x / (Pmol/P) (only the blue, bold, italic, text changes day to day) Verification of the gas dosage was carried out using a Shimadzu gas chromatograph GC-6AM, with FID (flame ionisation detector at 280 o C) and a SP 2401/SE 30 glass column. Helium was used as the carrier gas at 80 o C with an injection port temperature of 80 o C. Dosage was with headspace gas of 40ul per injection. Retention time for ethyl formate was 0.62 minutes. Gas concentration in the desiccators was checked 1 hour after dosage and 24 hours after dosage prior to unsealing the desiccators. Gas standards for the GC were made up each day. The range of the standards depending on the dosage. The standards were made up in Quickfit Erlenmeyer flasks with ground glass joints, of known volume (1.165, 1.197, l) and Quickfit cone adaptors with plastic cap and rubber septa. The dosage calculations for standards were calculated as above for gas dosage and gas volume (mls) removed prior to gas addition. Standard curves were graphed using Microsoft Excel with area/1000 on the x-axis and concentration on the y-axis. A trendline and R 2 equation was plotted from the standards data, with the slope equation used to estimate y intercept for each point. Figure 2.1. is an example of the generated curve and associated slope. 27

29 Shimadzu -EtF- 40 ul injection 8/2/00-10/2/00 Concentration EtF (mg/l) y1 = 0.145x R 2 = y2 = x R 2 = y3 = x R 2 = Area/1000 y1 y2 y3 Linear (y1) Linear (y3) Linear (y2) Figure 2.1 Examples of standard curves generated during the experiments. EtF = Ethyl formate. Insect mortality was calculated after the insects had been removed from the fumigation desiccators for 24 hours. Insects were kept at 25 o C on a small amount of food during this time. At this stage all dead insects were removed and counted. After a further 24 hours any insects which died were also removed and added to the mortality. (In these experiments mortality at 24 hours did not change with further incubation.) Results and Discussion Canberra insect cultures Initial observations were made with Canberra (SGRL) cultures of T. castaneum (Tc4), T. confusum (Tco37) and Ephestia kuehniella (Ek ; chosen due to it s similarity to raisin moth). Both adult and larval stages of the two beetles were observed along with the larval stage of the moth. Dosages of 0, 5, 10 and 20 gm -3 were selected as starting point concentrations for mortality studies, based on recent observations with Sitophilus species: a grain pest. From discussion it was felt that these dosages should give a range of mortalities including 100% (figure 2.2. and table 2.1). During the experiments the dosage range was adjusted as needed. Initial results showed quite low mortalities for the adult and larval stages of the flour beetles T. castaneum (Tc4) and T. confusum (Tco37). The mortality range for larval E. kuehniella (Ek) in the initial dosages was within expectations (Figure 2.2. and table 2.1). As a result a higher range of concentrations was selected for a second exposure (on Tuesday 8/2/00). This consisted of 0, 20, 40, 60 gm -3 of ethyl formate. 28

30 Table 2.1. Mortality of larvae, adults and pupae of three insect species when exposed to varying concentrations of ethyl formate in desiccators for 24 hours. Twenty insects from SGRL were in each sample, 5 samples per desiccator giving a total of 100 insects per desiccator. Carried out on 7 th and 8 th of February Sample Desired Conc. gm -3 Final Conc. gm -3 Ephestia kuehniella (larvae) Tribolium castaneum (adults) % mortality Tribolium castaneum (larvae) Tribolium confusum (adults) Tribolium confusum (larvae) (pupae) Figure 2.2. Mortality of three insect species exposed to varying concentrations of ethyl formate in desiccators for 24 hours, 20 insects per sample 7/2/00. EK = E. kueheniella, TC4 = T. castaneum, TCo37 = T. confusum. 29

31 Table 2.2 and Figure 2.3 show gas concentrations used and mortalities achieved during the second 24 hour fumigation on the 8 th and 9 th of February. Twenty T. confusum (Tco37) adults and larvae were placed in each desiccator. Then treated with ethyl formate at concentrations of 0, 20, 40, 60 gm -3. Table 2.2 Mortality of larvae and adults of T. confusum when exposed to varying concentrations of ethyl formate in desiccators for 24 hours on the 8 th and 9 th of February Twenty insects from SGRL were in each sample, N= 2 samples per desiccator giving a total of 40 insects per desiccator. 8/2/00 % mortality Desired Start Final T. confusum Conc. Conc. Conc. Tco37 (adults) Sample Desiccator gm -3 gm -3 gm -3 T. confusum Tco37 (larvae) Figure 2.3. Mortality of larvae and adults of T. confusum exposed to ethyl formate on 8/2/00 for 24hours Similar mortalities at 20gm -3 were achieved when compared to the first trial (Figure 2.1.) but 100% mortality at a dosage of 40 gm -3 indicated that at this stage a dosage range which included increments between 20 and 40gm -3, should probably give a range of mortalities from 0 to 100%, including 50 and 95% mortality for either Tco37 adults or larvae. To obtain a more replicable result larger numbers of insects were exposed to a dose range of 0, 20, 25, 30, 40 gm -3 in the 3 rd fumigation on the 9 th of Feb. The insects selected were Tco37 adults, Tc4 larvae and Oryzaephilus surinamensis (Os) adults. The adult Tco37 beetles were chosen because T. confusum are more numerous in Sunraysia than T. castaneum, while selection of Tc4 larvae was due 30

32 to a large number of these being available in a clean state already removed from food substrate and saving at least ½ a days work. O. surinamensis was included because it is the most numerous beetle pest in Sunraysia. Insects were weighed into the sample jars, using pre-estimated insect weights with the aim to add approximately 200 insects per jar. This was replicated twice and gave approximately 600 insects per desiccator. Adding insects above this level per desiccator was discussed but work at SGRL showed that both live and dead insects selectively sorb ethyl formate and it was feared that a higher quantity of insects may have caused reduced mortalities due to reduced fumigant concentrations and effectiveness. Thus we did not wish to investigate this at present, therefore the lower but still statistically significant levels of approximately insects per jar was chosen. Results are shown in table 2.3 and Figure 2.4. Table 2.3. Mortality of T. confusum adults, T. castaneum larvae and O. surinamensis adults when exposed to varying concentrations of ethyl formate in desiccators for 24 hours on 10/2/ Tc4 larvae weighed ~ 0.6g, 190 TCo37 adults weighed ~ 0.46g, 320 Os adults weighed ~ 0.16g each sample was replicated in separate desiccators giving approximately insects per desiccator. Sample Desired Conc. gm -3 Start Conc. gm -3 Final Conc. gm -3 Tribolium castaneum Tc4 (larvae) % mortality Tribolium confusum Tco37 (adults) Oryzaephilus surinamensis Os (adults)