The information here is provided by EcO2 B.V. for detailed study about technique used for the extermination of insects in food supplies and ships :

Abstract

The objective of this study was to investigate the possibility of using controlled atmosphere to exterminate insects and other pests at all stages of development in all kinds of food supplies, buildings, silos and ships. During the study, the following levels were monitored accurately: O2, CO2, N2, temperature and relative humidity. Experiments were conducted to test the efficacy of various percentages of the factors mentioned above in various combinations. The times needed for pest eradication varied with temperature, ranging from 2 to 9 days for stored product pests at 27-28oC and 9-10 days for the timber pest Xyleborus dryographus at 27oC. Mice and rats were controlled in warehouses by a 6-h exposure to a 16% O2 atmosphere achieved by purging with CO2 gas as an atmosphere replacement.

Introduction

The Montreal Protocol, has decided that the use of methyl bromide should gradually be discontinued in developed countries by 2005 and in developing countries by 2015. At present, the fumigant is used as a preplant soil sterilant and for the control of pests in buildings and food supplies. In the Netherlands the Ministry of Housing, Spatial Planning and the Environment instructed EcO2 to develop an alternative for this fumigant based on the principle of Controlled Atmosphere (CA). In collaboration with ‘TNO Industrie’ (the Netherlands Organization for Applied Scientific Research, section Industry), various tests were carried out with a variety of insects and pests, including Sitophilus spp., Rhyzopertha dominica, Tribolium spp., Plodia interpunctella, Ephestia spp., Blattella germanica, Xyleborus dryographus, Rattus norvegicus, Rattus rattus and Mus musculus domesticus.

The products and situations in which research was conducted, included rice and corn in grain silos and ships, various spices, cocoa beans, ginger, peanuts, furniture and floorboards in airtight environmental test chambers with a capacity of 160 m3.

The tests were carried out using a gas burner producing carbon dioxide (CO2), nitrogen (N2) and oxygen (O2) with an output capacity of 150 m3/h, the gas burner being fuelled with natural gas or propane gas and a 380V electric supply. The heat that is thus released is reused to heat the products by means of a closed circulation system, while at the same time it is used to control the relative humidity (r.h.) of the products during the treatment. To plan the tests, the research results reported by Annis (1987);, Bell and Armitage (1992), Banks and Fields (1995) and Navarro and Jay(1987) were used as guidance.

1. EcO2 technique for ships

The tests were carried out in six different ships, three filled with Surinam rice contaminated with Sitophilus oryzae, treating bulks of 400 t, 800 t, and 1500 t, and three filled with wheat contaminated with Plodia interpunctella, treating bulks of 500, 750 and 1500 t.

An injection system was installed in the cargo consisting of pipes, hoses and distribution stations to achieve optimal distribution of the inert gas, while at critical locations, meters were installed to measure the levels of O2, temperature and r.h. Once this was done, the ships holds were well sealed in order to guarantee that the Atmosphere composition required to exterminate the insects could be maintained.

The temperatures that were used on rice were 22°C and 28°C, at a r.h. of 50% and on wheat were 18°C and 27°C, at a r.h. of 50%. The Atmosphere applied contained 1% O2 and 12% CO2
The treatment times applied were 20 days at 22°C and 9 days at 28°C against S. oryzae on rice, and 6 days at 18°C, and 4 days at 27°C against P. interpunctella on wheat, in each case after achieving the target atmosphere, which, depending on the ship, required from 12 to 36 h. In all tests, all of the insect stages, eggs, larvae, pupae and adults, were exterminated. Samples taken after treatment that were stored in an incubator in the laboratory for 6 weeks following treatment, showed the same result.

In the holds there where placed, four test boxes, with approx. 6000 pcs off all stages of insects.

The study also investigated whether the CA technique left any residues on the rice cargo that was treated. No residues were identified.

2. EcO2 technique in Environmental Test Chamber 160 m3

During these tests, the following products were treated, which were contaminated with insects as follows:

Cocoa beans; Ephestia spp.
Ginger; Tribolium spp., Blattella germanica
Various spices; Rhyzopertha dominica
Furniture and floorboards; Xyleborus dryographus

The environmental test chambers were constructed from aluminium PUR panels, measuring 160 m3, which could be closed by gastight doors. A closed heat system was built in that allowed for separate product and room temperature control and monitoring. Humidity was controlled and monitored via the PLC. The whole installation is fully automated and computer-controlled. The controls and drives can be regulated and adjusted by remote control.

The conditions in which these tests were conducted varied per product, as listed below.

Cocoa beans, Ephestia spp.; 18° C and 27° C at 40% r.h., air composition consisting of 1% O2 and 11½% CO2.

Ginger, Tribolium spp.; 18° C and 28° C at 50% r.h., air composition consisting of < 1% O2 and 12% CO2.

Ginger, Blattella germanica; 28° C and 45º C at 50% r.h., air composition consisting of < 1% O2 and 11½% CO2.

Various spices, Rhyzopertha dominica; 15º C and 27º C at 45% r.h., air composition consisting of < 1½% O2 and 12% CO2.

Furniture, floorboards, Anobium punctatum, Xyleborus dryographus; 25º C and 30º C at 50% r.h., air composition consisting of < 1% O2 and 11½% CO2.

A) Test with cocoa beans contaminated with Ephestia spp.;

For this test a total of 3000 tons of cocoa beans were treated, half at 18º C and 40% r.h. for a test period of 6 days, and the other half at 27º C and 40% r.h. for a test period of 4 days. After reaching the correct atmosphere, the time, which was needed to achieve the pull down, took 12 hours.

The cocoa beans were placed on pallets in the environmental test chamber, including 4 test boxes of Ephestia in all stages, following with the doors closed and the installation switched on. Heating the product to 18º C took 12 h, and to 27º C took 18 h. During the test, at 18oC, 6 days, 4 days after reaching the required experimental conditions, the 4 test boxes were removed from the environmental test chamber and placed in an incubator at 28º C and 40% r.h. A similar operation was performed after 4 days in the experiment at 27oC.

After six weeks, the test boxes were removed from the incubator and investigated by ‘Handels Laboratorium Verweij’ in Rotterdam. No survival of eggs, larvae, pupae or adults was recorded at either temperature. An estimated of each stage was present in the samples.

B) Test with ginger contaminated with Tribolium spp.;

For this test, we treated a total of 1000 tons of ginger, of which 500 tons at 18º C and 50% r.h. for a test period of 5 days, and 500 tons at 28º C and 50% r.h. for a test period of 2 days. It took 7 hours to reach the pull down.

For the experiment at each temperature, the ginger was placed on pallets in the environmental test chamber, including 4 test boxes of Tribolium in all stages, following which the doors were closed and the installation was switched on. Heating the product 18º C took 8 h and to 28º C took 12 h. During the tests, 5 days after reaching experimental conditions at 18oC and 2 days after reaching experimental conditions at 28oC, the 4 test boxes were removed from the environmental test chamber and placed in a kiln at 28º C and 50% r.h..

After six weeks, the test boxes were removed from the kiln and investigated by ‘Handels Laboratorium Verweij’ in Rotterdam. No survivals from an estimated minimum sample size of 8.000 pcs of each stage at either temperature were recorded.

C) Test with ginger contaminated with Blattella germanica;

For this test, a total of 500 tons of ginger was treated, of which 300 tons were exposed at 28º C and 50% r.h. for a test period of 6 days, and 200 tons at 45º C and 50% r.h. for a test period of 9 days. Exclusive of the time to attain test conditions. The time to reach the pull down took 12 hours.

For the test at each temperature, the ginger was placed on pallets in the environmental test chamber, including 4 test boxes of B. germanica in all stages, following which the doors were closed and the installation was switched on. Heating the product to 28º C took 12 h and to 45º C took 18 h. During the test, 6 days after reaching the target conditions at 28oC, and 9 days afterwards at 45oC, the 4 test boxes were removed from the environmental test chamber and placed in an incubator at 28º C and 50% r.h..

After six weeks, the test boxes were removed from the kiln and investigated by ‘Handels Laboratorium Verweij’ in Rotterdam. The results obtained are shown in Table 1.

Table 1. Mortality of Blatella germanica in consignments of ginger exposed in the EcO2 CA chamber

(N) Based on a sample size of approx. 4.000 pcs of all stages in each test box.

D) Test with various spices contaminated with Rhyzopertha dominica;

For this test, a total of 800 tons of spices was treated, of which 300 tons were exposed at 15º C and 45% r.h. for a test period of 12 days, and 500 tons at 27º C and 45% r.h. for a test period of 6 days, after establishing experimental conditions.

The spices were placed on pallets in the environmental test chamber, including 4 test boxes of R. dominica in all stages, following which the doors were closed and the installation was switched on. Heating the product to 15º C took 6 h, and to 27º C, 14 h. During the test, 12 days after reaching experimental conditions at 15oC, and after 6 days at 27oC, the 4 test boxes were removed from the environmental test chamber and placed in an incubator at 28º C and 45% r.h..

After six weeks, the test boxes were removed from the kiln and investigated by ‘Handels Laboratorium Verweij’ in Rotterdam. No survivals from an estimated minimum sample size of approx. 7.500 pcs of each stage at either temperature were recorded.

E) Test with furniture contaminated with Xyleborus dryographus;

For these tests, a total of 600 pieces of furniture were treated, of which 150 pieces were exposed at 15º C and at 45% r.h. for a test period of 20 days, 300 pieces at 22º C and at 45% r.h. for a test period of 15 days and 150 pieces at 27º C and at 45% r.h. for a test period of 10 days, exclusive of pull-down.

For the test at each temperature, the furniture was placed in the environmental test chamber, together with 4 test boxes of X. dryographus in all stages, following which the doors were closed and the installation was switched on. Heating the product to 15º C took 20 hours, to 22º C, 28 h and to 27º C, 36 h. During the tests, 20, 15 and 10 days respectively after arrival at the target conditions, the 4 test boxes were removed from the environmental test chamber and placed in an incubator at 28º C and 45% r.h..

After six weeks, the test boxes were removed from the kiln and investigated by ‘Handels Laboratorium Verweij’ in Rotterdam. The results obtained are summarised in Table 2.

Table 2. Mortality of Xyleborus dryographus exposed with furniture in the EcO2 CA chamber

F) Test with floorboards contaminated with Xyleborus dryographus;

For this test, we treated a total of 1000 M3 of floorboards, of which 300 M3 at 15º C and 55% r.h. for a test period of 18 days, 400 M3 at 22º C and 55% r.h. for a test period of 14 days and 300 M3 at 27º C and 55% r.h. for a test period of 9 days, exclusive of pull-down.

For the test at each temperature, floorboards were placed in the environmental test chamber, together with 4 test boxes of X. dryographus in all stages, following which the doors were closed and the installation was switched on. Heating the product to 15º C took 12 h, to 22º C, 18 h, and to 27º C, 22 h. During the test, 18, 14 and 9 days respectively after reaching target conditions, the 4 test boxes were removed from the environmental test chamber and placed in an incubator at 28º C and 45% r.h..

After six weeks, the test boxes were removed from the kiln and investigated by ‘Handels Laboratorium Verweij’ in Rotterdam. Results are summarised in Table 3.

Table 3. Mortality of Xyleborus dryographus exposed with floorboards in the EcO2 CA chamber

(N) Based on a sample size of approx 2.700 pcs of all stages in each test box.

3. EcO2 technique in buildings and storage sheds

A) Storage shed contaminated with Rattus rattus and Mus musculus domesticus;

For this test, two storage sheds were treated, of volumes 100,000 m3 and 200,000 m3. Since the temperature level is of no importance in this type of treatment, only O2 measuring points were installed in the buildings during the tests. The objective of the tests was to find out what quantity of CO2 would be required to exterminate Rattus rattus/norvegicus and Mus musculus domesticus in buildings, expressed as a percentage of the total volume to be treated.

In each of the storage sheds,, an injection system consisting of pipes, hoses and distribution stations was installed, in order to achieve better distribution of the inert gas, while at critical locations, O2 meters were installed. Once this was done, each shed was sealed off to be as gastight as possible in order to achieve the air composition required to exterminate the pest. The target for control was set as the lowering of O2 to 16% of the atmosphere (Cassells et al., 1997).

For the 100,000 m3 shed the air composition reached 16% O2 after application of 50% of the volume of the building of CO2, whereas for the 200,000 m3 building, only CO2 to the level of 25% of the volume of the building was used.

From the time of reaching pull-down to 16% O2, the treatment time decided was 6 h exclusive of installation and break-down of the injection system, sealing activities and declaring the shed to be gas-free.

The CA technique did not leave any residual effect on the goods stored in the shed.

Conclusions

Based on the results yielded by the tests, we reached the conclusion that the EcO2 technique, based on the principle of Controlled Atmosphere, constitutes a good alternative for methyl bromide and also for phosphine. The studies furthermore show that the technique leaves no residues on the treated products.

What became apparent from the tests, was that the time required for treatment depended on the following data: correct temperature level, air composition, r.h., type of product and type of pest present.

Initially, the tests with Blattella germanica, for example, failed due to the fact that the temperature level was set too low, resulting in too short a period of treatment. Following further research, it was decided to repeat the test at a higher temperature level. This means that if a lower temperature of approximately 28º C is applied, it is recommended that the time of treatment should be extended to at least 12 days from the 6 days tested here.

The other tests, apart from the furniture and floorboards, showed that treatment at lower temperatures and for extended periods of time will produce the desired result. However, with an average temperature of between 25º and 27º C and the right air composition, the EcO2 technique constitutes a very good and economically sound alternative.

The tests with furniture and floorboards showed that the method fails to achieve results at a lower temperature and with the period of treatment that was applied. Extended periods of treatment will be required which, however, do not constitute an economically sound option. The ideal temperature for treatment, therefore, is 27º C.

Finally, it should be point out that the studies mentioned form only part of the total volume of studies conducted by EcO2 over the past years. The EcO2 technique for buildings proved very successful in the tests, due, to some extent, to the speed of treatment – approximately 6 hours after reaching pull-down – and the absence of constraints due to statutory regulations and distance requirements, making this a technique that can be applied quickly and in any location and one that is economically feasible.

Acknowledgement

We hereby express our gratitude for the research and supervision by Job Klijnstra of the TNO Institute of Industrial Technology in the Netherlands, and the guidance of Joop van Haasteren of the Ministry for Housing, Spatial Planning and the Environment in the Netherlands.

References