STORING AGRICULTURAL PRODUCTS UNDER MODIFIED ATMOSPHERES

Firstly we should like to refer you to our ecosystem page. Having read this, you will appreciate that this conservation principle is based on manipulation of the atmospheric component of the ecosystem. We mantain the same atmospheric gases, (nitrogen, oxygen and carbon dioxide) but alter their ratios to reduce the proportion of oxygen. The MA method is of special interest in that it is the only fumigation alternative that enables one to carry out insect control in-situ. Although this method has been well researched, its commercial use until recently, has been rather limited. Possible reasons for its lack of commercial acceptance were its higher cost (in comparison with fumigation) and a lack of sufficient information on its reliability. However, cost comparisons between fumigation and alternative methods must be weighted against consumer acceptance, and as for its reliability, the extensive research (including our own contribution) on the effects of MAs on insects has provided a firm basis for the technology, and its potential to largely replace conventional fumigation.
The application of MAs and fumigants is most appropriate for bulk storage of grain either on-farm, or at central storage installations which are gastight according to accepted standards. High value commodities requiring treatment in relatively small lots may be treated in specially designed fumigation chambers that may be adapted for MA application, or in flexible plastic containers which are also suitable for bag and crate storage. Hermetic storage to which we have devoted a separate web-page, is in fact a special case of MA, where the living components of the ecosystem "bio-generate" their own atmosphere by their respiratory metabolism.
To complete this overview we shall describe the methods of MA generation and application, with emphasis on the main differences between them, and point out how our own work can promote the use of MAs as a fumigation alternative.

Generation of Modified Atmospheres

The objective is to attain a composition of atmospheric gases rich in CO₂, or in N₂, and low in O₂, or a combination of these gases within the storage enclosure or treatment chamber, for the time necessary to control the storage pests. At present, the most widely used source for production of such atmospheric gas compositions is tanker-delivered liquefied CO₂ or N₂. Availability and suitability of this means of gas supply must be questioned when the gases are transported over long distances from an industrial production area to the storage site. Therefore, alternative potential methods of generating MAs should also be considered.

1. Supply of Gases from Tankers
   When the target MA gas composition is <1% O₂ or high CO₂ concentration, a commonly used method is to supply N₂ or CO₂ from pressurized tankers. The practical aspects of purging grain storages have been described by Guiffre and Segal (1984) for CO₂, and by Banks et al. (1980) for N₂ and CO₂. A significant portion of the cost of applying MAs generated from tankers is for transportation and on-site purging. Bulk liquid gas is transported in conventionally insulated road tankers.
   For large-scale application of N₂ or CO₂, vapourizers are essential. These vapourizers consist of a suitably designed receptacle with a heating medium (electricity, steam, diesel fuel or propane), a hot-water-jacketed super-heated coil, and forced or natural draught. A forced-draught-type vapourizer with electrical super heating was found to be convenient.

2. Exothermic Gas Generators
   For on-site generation of MAs by combustion of hydrocarbon fuel to produce a low O₂ atmosphere containing some CO₂, commercial installations -termed exothermic gas generators or gas burners- are available. Such equipment was originally designed for MA storage of fresh fruits. Their MA composition is designed to allow the presence of approx. 2-3% O₂ and to remove CO₂ through scrubbers. Therefore, their use in the grain industry requires several adaptations, like tuning the equipment to obtain an O₂ level of <1%; utilization to full advantage of the CO₂ generated; and removal of excessive humidity from the atmosphere generated. Combustion of propane yields approx. 13%CO₂, and of butane approx. 15% CO₂. The MA generated is more toxic than a N₂ atmosphere deficient in O₂. This is due to the presence of CO₂ in the MA causing hypercarbia which together with hypoxia are synergistic in their effect on insect mortality. Equipment has been designed to operate with open flame burners, catalytic burners, and as internal combustion systems. Full-scale field trials using open flame burners (exothermic MA generators), and catalytic burners to provide a low O₂ gas mixture, have proved successful. Open flame burners are capable of producing high gas flow rates at low O₂ tension. Consequently, the generated MA can be applied directly to purge the treated enclosure. On the other hand, catalytic systems reduce the O₂ concentration in the atmosphere by a fixed fraction during passage through the catalyst, and therefore should be used preferably in a recirculation system. The development of a modified internal combustion engine for MA generation has also been reported. In spite of its advantages over the open flame and catalytic burners as an easily operated, transportable and independent system, information on field application of such combustion systems is lacking.

3. On-site N₂ Generators
   Commercial equipment, termed also "pressure-swing adsorption" systems, using the process of O₂ adsorption from compressed air passed through a molecular sieve bed, is available. For continuous operation a set of two adsorbers is provided, which operate sequentially for O₂ adsorption and regeneration. N₂ at a purity of 99.9% can be obtained through regulation of inlet air-flow. This method of N₂ generation is a relatively new approach in MA generation technology. Equipment is now being manufactured that is rated to supply an outlet flow rate of 120m³/h at an outlet purity of 98% N₂. However, in view of the high capital cost investment involved, it would seem wise to undertake a long-term cost-benefit analysis to explore the justification of usage of these installations.

4. Biogeneration of MAs
   Two principal forms of biogeneration of MAs exist, namely, "Hermetic storage" and "Assisted hermetic storage".
   Assisted hermetic storage: The term "assisted hermetic storage" was introduced by Banks (1984) in order to define a process in which MA generation is assisted by a biogenerator source without sacrificing the commodity. Using a similar approach, Calderon et al. (1981) examined the possibility of generating a MA by inoculating wet rice bran. The best known working example of assisted hermetic storage is that in use in China. With this method, removal of O₂ is achieved by recirculating storage gases through a closed system containing racks of moist grain and bran infected with a particular mould culture. This MA generation system merits further attention to explore potential applications at locations where a regular supply of industrial gases is non-existent or economically unfeasible.

METHODS FOR APPLYING MODIFIED ATMOSPHERES

Choice of Atmospheric Gas Composition
A simple and descriptive graphical presentation to illustrate the relationship between exposure period, O₂ and CO₂ concentration (at normal atmospheric pressure), and mortality of different insects life stages, was compiled from the literature by Annis (1987). In his review, he proposed provisional dosage regimes at grain temperatures of 20-29 °C.
A summary of these dosage regimes is given in Table 1, which shows that the use of an atmosphere with less than 1% O₂ requires considerably longer exposure times than 80% CO₂ atmospheres to kill insect populations other than Trogoderma granarium. The basis for preparing these regimes was the time response of the most tolerant developmental stage of the most tolerant insect species. In the absence of T. granarium, a low O₂ regime should be based on the response of S. oryzae pupae, while the CO₂ regimes should be based on Tribolium castaneum adults and larvae (Annis, 1987; Navarro and Jay, 1987).
Dosage regimes presented in Table 1 should be viewed as very generalized recommendations. More recently published information (Navarro and Jay, 1987; Reichmuth, 1987; Jay et al., 1990) indicates that further work is needed to enable precise dosage recommendations to be established for the application of MAs for the major stored-product insects under the wide range of intrinsic and extrinsic factors involved. Thus, recommended dosage regimes should be based on temperature ranges appropriate to specific climatic conditions and also to the dominant insect species found in the commodities involved. Aspects of commodity moisture content (Bell, 1987; Navarro, 1978), socioeconomically acceptable control levels, the time-frame within which control must be accomplished, and the expected leak-rate standard in which the MA treatment will be performed will probably all play an important role in future recommendations.

Table 1. Suggested provisional dosage regimes for control of all stages of the 12 most common insect species of stored grain, using modified atmospheres at temperatures between 20 and 29°C*.

Atmospheric gas concentration	Controls most common grain insects including Trogoderma granarium (yes/no)	Exposure period (days)
<1% O2 (in nitrogen)	yes	20
Constant % CO2 in air
40	no	17
60	no	11
80	no	8.5
80	yes	16
CO2 decay in air from >70 to 35%	no	15
Pressurized CO2 at >20 bar	**	<0.08

* Data, except those on pressurized CO₂, compiled from Annis (1987) . ** Available data are based only on Plodia interpunctella and Lasioderma serricorne.

High Pressure CO₂ application: In contrast to the conventional application of MAs at normal atmospheric pressure, the use of pressurized CO₂ in high-pressure chambers has been developed recently. Special equipment needed to withstand the high CO₂ pressure is expensive and therefore limits the market of this method. However, food industry processing high-value products such as drugs and spices may take advantage of this MA method in the future as well as the disinfestation of museum artifacts and other special commodities. The mode of action appears to be based on the rapid expansion of bubbles of CO₂ dissolved in the body fluids of the insects as the high pressure is released - somewhat similar to the "bends" experienced by divers.

Rate of Supply

Due to the relatively long exposure time involved, one basic concept with MA application methods is the combination of two separate phases: an initial 'purge' for the establishment of the desired atmospheric gas composition, and a subsequent 'maintenance' phase in which the desired gas composition is maintained during the exposure period (Banks and Annis, 1977). This concept differs from the 'single-shot' treatment suggested by Banks et al. (1980). This latter-type treatment is suitable basically for CO₂ when an initial concentration of higher than 70% is established and the gastightness of the structure is sufficient to allow maintenance of a concentration at above 35% for at least 10 days.
With MA treatment a large volume of the intergranular free space plus the headspace of the silo needs to be displaced. The rate of gas supply is purely an economic aspect of the application of MA s, since a substantial portion of the expense involved consists of the cost of transporting the liquid CO₂ or N₂ and of the on-site purging, which is a time-consuming process (Guiffre and Segal, 1984). If on-site bulk gas tanks are not installed, truck demurrage charges must be added. With gas burners the aspect of transportation is less critical, since the quantities of hydrocarbon gas used are considerably less.
The gas supply rates required for the application of selected MA s are listed in Table 2. The proposed supply time at 'purge' phase for a MA of <1% O₂ is considerably shorter than for the other MA s applied at normal atmospheric pressure. This shorter 'purge' time derives from the physical characteristics of N₂ (Banks and Annis, 1977). A method (not included in Table 2) that has been used by us in small bins of 50-tonne capacity consists of direct gas supply to the bin in a liquid state, thereby reducing the supply time considerably. This method is discussed in the section on gas supply in a liquid state.
The shortest supply time is achievable using pressurized CO₂ system (Table 2). The natural pressure of liquid CO₂ is advantageous in creating high pressure in the exposure chamber.

Table 2. Rates of gas supply requirements for modified atmosphere application.

Selected atmospheric gas concentration	Application phase	Amount of gas per tonne commodity	Supply time (h)
<1% O2 in N2	Purge	1-2 m3 N2	<12
	Maintenance	0.01-0.06 m3 N2	**
>70% CO2 in air	Purge	0.5-1.9 m3 CO2	<48
	Maintenance	0.02-0.04 m3 CO2	**
Gas burner <1% O2 with >14% CO2	Purge	17-66 g C3 H8	<48
	Maintenance	0.6-1.2 g C3 H8	**
>70% CO2 in air	Single-shot	0.5-1.0 m3 CO2	<48
Pressurized CO2 at >20 bar	Single-shot	>18 kg CO2	<0.5

* Compiled from Banks (1984a) (except data on pressurized CO₂). Only gas composition supported by field experience are presented in this table. Basic assumptions for above requirements are: that storage is filled with grain (minimum headspace) and pressure decay time is <5 mins for decay from 500 to 250 Pa.
** According to the dosage regime, see also Table 1.

Structural Requirements

Storage structures designed specifically for the application of MA s are practically non-existent, apart from those in Australia. According to Banks and Ripp (1984) there is in Australia an increasing trend toward the use of sealed storage for dry grain, accompanied by the conversion of existing structures to sealed storage rather than construction of new installations. Large-scale operations of this type have not yet been reported from other parts of the world. Therefore, before deciding on the method of MA application, careful examination should be made of sealing requirements to obtain a standard acceptable for maintaining the gas composition over the designed exposure period. For application of pressurized CO₂, especially designed chambers and installations to withstand the high pressures are needed.

Application of MA in a Gaseous State

For application of N₂ or CO₂ into upright storages, simple inlet systems fitted into the bin wall can be used for gas introduction. The design of the system should be such as to prevent excessive pressure buildup over weak areas of the silo bin wall, especially around the inlet pipe. For purge rates of 6m³/min. an inlet pipe of 8 cm diameter has proven convenien . However, in bins equipped with a grain aeration system, it is advantageous to use the inlet duct system as the gas introduction point in order to obtain improved purging efficiency.
When purging upwards, high CO₂levels tend to remain in the lower layers of large bins and this may result in uneven and sometimes inadequate CO₂ concentrations for insect control, especially in the upper layers of bins. To overcome this, especially in the 'single-shot' CO₂ application method where no maintenance phase is used, it is important to introduce an air injector into the CO₂ stream so as to produce a CO₂-air pre-mix at the designed concentration, or to recirculate the CO₂-air mixture until the desired CO₂ concentration is attained in all regions of the bin.
For the application of CO₂, Jay (1971; 1980) proposed three methods. These, together with the recirculation and blending method comprise the five basic application methods suitable for MA s at normal atmospheric pressure. They are summarized in Table 3 and presented schematically in the figure. Recirculation gives the most uniform concentration and it can be applied by moving the gases inside the bins upwards or downwards (Navarro et al., 1986). The main gain in using downwards flow is with application by burner gas. It permits advantage to be taken of the long path of the external gas delivery pipe to cool and thereby dehumidify the hot gases after the burner.
The pressurized CO₂ method is most advantageous when extremely short exposure time is a pre-condition (Table 3, method 6).

Application of MA in Liquid or Solid State

For small silos (including GrainPro Cocoons) and MA treatment chambers of up to 100 m³, a direct supply of CO₂ from cylinders equipped with a siphon, or that can be inverted with a bascule, is feasible. By this means, CO₂ is released in a liquid state from the pressurized cylinder.
A large volume of CO₂ can thus be introduced into the treated enclosure in a relatively short time, thereby causing displacement by lift-out of a substantial portion of the atmosphere from the free space of the treated structure. Great care should therefore be taken to install a large enough vent pipe and to ensure that the structure can withstand the pressure build-up at the initial purging phase. In addition, it is strongly recommended that the pressure of the treated structure be monitored. Our experience with this method of gas supply has been that at a rate of 4 m³ CO₂/min, the pressure build-up within a chamber of 110 m³ was less than 60 Pa when the vent pipe's internal diameter was 75 mm. Application of CO₂ in the form of dry ice to control insects infesting flour in hopper cars and in freight containers has been investigated. The results indicate that further field trials are needed before recommending this method of application under commercial conditions.

Table 3. Methods of application of modified atmospheres

Methods of application	Applicable MA	Main advantages	Main disadvantages	Reference
1. Purge a full silo from the top.	CO2	Requires only one application. Labour requirements are minimal.	Purging time is long. Some CO2 is lost in outflow with air mix.	(4) (5)
2. Apply CO2 in the grain stream (snow, dry ice).	CO2	Method is fast. No vaporization equipment is needed.	Danger of explosion (static electricity). Constant supervision during application.	(4)
3. Lift the atmosphere out (air displacement method).Continuous purge from bottom.	CO2 N2 GB*	Labour requirements are low. No loss of gas in mixing. Works best with N2.	Gas purging region of silo should be leak-free. With CO2 it creates high localized concentration, so blending may be necessary.	(1)(2)(4)(7)
4. Blending and purging.	CO2	Homogenous concentration is obtained. No loss of gas in mixing.	Air CO2 mixing equipment is necessary.	(8)
5. Recirculation.	CO2 GB	Homogenous concentration is obtained. No loss of gas in mixing.	Recirculation equipment is necessary.	(6) (8)
6. Pressurized CO2 at >20 bar	CO2	Short exposure time required for complete control.	Method is costly and needs special exposure chamber.	(3)

* GB, gas burner atmosphere, consisting of <1%O₂, 15% CO₂, and 84% N₂.
** (1) = Banks and Annis (1977).
(2) = Fleurat Lessard and Le Torc'h (1987).
(3) = Gerard et al. (1988).
(4) = Jay (1980).
(5) = Jay and Pearman (1973).
(6) = Navarro et al. (1979).
(7) = Storey (1973).
(8) = Wilson et al. (1984).

SLIDE SHOW: This is a series of 10 slides showing various aspects of our investigations.

For Netscape 6 users you may need to move slide-window to front

WE'VE SEPARATED OUR OWN PAPERS INTO BIOLOGICAL/PHYSIOLOGICAL STUDIES, AND COMMERCIAL SCALE TRIALS.

Calderon, M. and Navarro, S. (1979) Increased toxicity of low oxygen atmospheres supplemented with carbon dioxide on Tribolium castaneum adults. Ent. exp. et. appl. 25: 39-44.

Calderon, M. and Navarro, S. (1980) Synergistic effect of CO2 and O2 mixture on stored grain insects. Proc. Symp. Cont. Atmosph. Storage, Rome: 79-84.

Donahaye, E. and Navarro, S. (1988). Sensitivity of two dried fruit pests to methyl bromide alone, and in combination with carbon dioxide or under reduced pressure. Trop. Sci. 29: 9-14.

Donahaye, E. (1990). Laboratory selection for resistance by the red flour beetle Tribolium castaneum Herbst.) To an atmosphere of low oxygen concentration. Phytoparasitica 18: 189-202.

Donahaye, E. (1990). Laboratory selection of resistance by the red flour beetle Tribolium castaneum (Herbst.) to a carbon dioxide enriched atmosphere. Phytoparasitica 18: 299-308.

Donahaye, E. (1992). Physiological differences between strains of Tribolium castaneum selected for resistance to hypoxia and hypercarbia, and the unselected strain. Physiological Entomology 17: 219-229.

Donahaye, E., Daliah Salach and Miriam Rindner (1992). Comparison of the sensitivity of the developmental stages of three strains of the red flour beetle, Tribolium castaneum (Herbst), to modified atmospheres J Econ. Ent
85:1450-1452.

Donahaye, E. (1993). Biological differences between strains of Tribolium castaneum selected for resistance to hypoxia and hypercarbia, and the unselected strains. Physiological Entomology 18, 247-250.

Donahaye, E.J., Navarro, S. Miriam Rindner and Azrieli, A. (1996) The combined influence of temperature and modified atmospheres on Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). J. stored Prod. Res. 32: 225-232.

Friedlander, A. and Navarro, S. (1979) Triglyceride metabolism in Ephestia cautella pupae exposed to carbon dioxide. Experientia 35: 1424-1425.

Friedlander, A. and Navarro, S. (1979) The effect of controlled atmospheres on carbohydrate metabolism in the tissue of Ephestia cautella (Wlk.) pupae. Insect Biochem 9: 79-83.

Friedlander, A., and Navarro, S. (1983) Effect of controlled atmospheres on the sorbitol pathway in Ephestia cautella (Walker) pupae. Experientia 39: 744-746.

Friedlander, A., Navarro, S. and Silhacek, D.L. (1983) The effect of carbon dioxide on NADPH production in Ephestia cautella (Wlk.) pupae. Comp. Biochem. and Physiol. 77B,4:839-842.

Friedlander, A. and Navarro, S. (1984) The glutathione status of Ephestia cautella (Walker) pupae exposed to carbon dioxide. Comp. Biochem. and Physiol. 79C, 1: 217-218.

Navarro, S. and Donahaye, E. (1972) An apparatus for studying the effects of controlled low pressures and composition of atmospheric gases on insects. J. stored Prod. Res. 8: 209-212.

Navarro, S. and Calderon, M. (1973) Carbon dioxide and relative humidity: interrelated factors affecting the loss of water and mortality of Ephestia cautella (Wlk.) (Lepidoptera, Phycitidae). Israel Jour. of Entomology 8: 143-152.

Navarro, S. and Calderon, M. (1974) Exposure of Ephestia cautella (Wlk.) pupae to carbon dioxide concentrations at different relative humidities: The effect on adult emergence and loss in weight. J. stored Prod. Res. 10: 237-241.

Navarro, S. and Friedlander, A. (1974) The effect of carbon dioxide anesthesia on the lactate and pyruvate levels in the hemolymph of Ephestia cautella (Wlk.) pupae. Comp. Biochem. Physiol. 50 B:187-189.

Navarro, S. (1978) The effect of low oxygen tensions on three stored-product insect pests. Phystoparasitica 6: (2) 51-58.

Navarro, S., Amos, T.G. and Williams, P. (1981) The effect of oxygen and carbon dioxide gradients on the vertical dispersion of grain insects in wheat J. stored Prod. Res. 17: 101-107.

Navarro, S., Lider, O. and Gerson, U. (1985) Response of adults of the grain mite, Acarus siro L. to modified atmospheres. J. Agric. Entomol. 2(1): 61-68.

Navarro, S., Dias, R. and Donahaye, E. (1985). Induced tolerance of Sitophilus oryzae adults to carbon dioxide. J. stored Prod. Res. 21: 207-214.

Tunç, I. and Navarro, S. (1983) Sensitivity of Tribolium castaneum eggs to modified atmospheres. Ent. exp. et. appl. 34: 221-226.

Rindner, Miriam, S. Navarro, E. Donahaye, R. Dias A. Azrieli and Glory Sabio (200). The combined effect of heat and CO₂ on diapausing larvae of the khapra beetle Trogoderma granarium. (Accepted for publication in Proc. CAF Conference, Fresno Ca. Oct 2000)

Zettler, J.L. and Navarro, S.(2001). Effect of modified atmospheres on microflora and respiration of California prunes. In: Donahaye, E.J., Navarro, S. and Leesch J.G. [Eds.] (2001) Proc. Int. Conf. Controlled Atmosphere and Fumigation in Stored Products, Fresno, CA. 29 Oct. - 3 Nov. 2000, Executive Printing Services, Clovis, CA, U.S.A. pp. 26-35
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Navarro, S. (2000). III- Critical limits of degree of sealing for successful application of controlled atmosphere or fumigation. In: Donahaye, E.J., Navarro, S. and Leesch J.G. [Eds.] (2001) Proc. Int. Conf. Controlled Atmosphere and Fumigation in Stored Products, Fresno, CA. 29 Oct. - 3 Nov. 2000, Executive Printing Services, Clovis, CA, U.S.A. pp. 507-520
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Navarro, S. Donahaye, E. Miriam Rindner and Azrieli A. (2000). Storage of dates under carbon dioxide atmosphere for quality preservation. In: Donahaye, E.J., Navarro, S. and Leesch J.G. [Eds.] (2001) Proc. Int. Conf. Controlled Atmosphere and Fumigation in Stored Products, Fresno, CA. 29 Oct. - 3 Nov. 2000, Executive Printing Services, Clovis, CA, U.S.A. pp. 307-315
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Commercial-scale trials:

Navarro, S. Gonen, M. and Schwartz, A. (1979) Large scale trials on the use of modified atmospheres for the control of stored grain insects. Proceeding of the Second International Working Conference on stored product entomology, September 1978, Ibadan, 260-270.

Navarro, S., Jay, E.G., and Leesch, J.G. (1986) Recirculation rate requirements for adequate distribution of carbon dioxide in grain silos. Transactions of the ASAE 29(5): 1348-1354.

Navarro, S., and Jay, E. G. (1987) Application of modified atmospheres for controlling stored grain insects. BCPC Monograph No. 37. Stored Products Pest Control, 37, 229-236.

Williams, P., Minett, W., Navarro, S. and Amos, T.G. (1980) Sealing a farm silo for insect control by nitrogen swamping for fumigation. Aust. J. Exp. Anim. Husb. 20: 108-114.

Here are the other references cited on this page

Annis P. C. (1987) Towards rational modified atmosphere dosage schedules: a review of current knowledge. Proc. 4th Int. Conf. Stored-Product Protection, Tel-Aviv, Israel, Sep. 1986, 128-148.

Banks H. J. (1984a) Current methods and potential system for production of modified atmospheres for grain storage. Modified Atmosphere and Fumigation in grain Storages, 523-542.

Banks H. J. (1984b) Assessment of sealant systems for treatment of concrete grain storage bins to permit their use with fumigants or modified atmospheres: laboratory and full scale tests. CSIRO, Div. of Entomol., 38pp.

Banks H. J. and Annis P. C. (1977) Suggested procedures for modified atmosphere storage of dry grain. Division of Entomology Technical Paper CSIRO, AUSTRALIA, No. 13, 23pp.

Banks H. J. and Annis P. C. (1980) Conversion of existing grain storge structures for modified atmosphere use. Modified Atmosphere Storage of Grains, Amsterdam, Elsevier, 461-473.

Banks, H.J., Annis, P.C., Henning, R.C., and Wilson, A.D. (1980) Experimental and commercial modified atmosphere treatments of stored grain in Australia, In: Shejbal, J. ed. Modified Atmosphere Storage of Grains. Amsterdam, Elsevier, 207-224.

Banks, H. J., and Ripp, B. E. (1984) Sealing of grain storages for use with fumigants and modified atmospheres. Proceedings of the 3rd International Working Conference on Stored-Product Entomology. Manhattan, Kansas, USA. October 1983. 375-390.

Bell, C. H. (1987) Effect of grain moisture content on the establishment and maintenance of a low oxygen atmosphere containing carbon dioxide. BCPC Monograph No. 37. Stored Products Pest Control, 37, 237-246.

Fleurat Lessard, F., and Le Torc'h J. M. (1987) Practical approach to purging grain with low oxygen atmosphere for disinfestation of large wheat bins against the granary weevil, Sitophilus granarius. In: Donahaye, E., and Navarro, S. ed. Proceedings of the 4th International Working Conference on Stored-Product Protection. Tel Aviv, Israel. September 1986. 208-217.

Gerard D., Kraus J., and Quirin, K. W. (1988) Rueckstandsfreie Durckentwesung mit natuerlicher Kohlensaeure. (Residue free insect control using natural carbon dioxide under high pressure). Gordian, 88:90-94.

Guiffre, V., and Segal, A. I. (1984) Practical approaches to purging grain storages with carbon dioxide in Australia. In: Ripp, B. E., et al., ed., Modified atmosphere and fumigation in grain storages. Amsterdam, Elsevier, 343-358.

Jay, E. (1971) Suggested conditions and procedures for using carbon dioxide to control insects in grain storage facilities. USDA, ARS 51-46: 6p.

Jay, E. (1980) Methods of applying carbon dioxide for insect control in stored grain. AAT-S-13, No. 13,1-7.

Jay, E., and d'Orazio, R. (1984) Progress in the use of modified atmosphere in actual field situations in the United States. In: Ripp, B. E., et al., ed., Modified Atmosphere and Fumigation in Grain Storages. Amsterdam, Elsevier. 3-13.

Jay, E.G., and Pearman, C. G. (1973) Carbon dioxide for control of an insect infestation in stored corn (maize). J. Stored Prod. Res. 9, 25-29.

Jay, E.G., Banks, H. J., and Keever, D. W. (1990) Recent developments in modified atmosphere technology. In Champ, B. R., Highley, E., and Banks, H. J. (eds) Fumigation and Modified Atmosphere Storage of Grain. February 1989, Singapore. ACIAR Proc. No. 25.134-143.

Reichmuth, C. (1987) Low oxygen content to control stored product insects. In: Donahaye, E., and Navarro, S., ed., Proceedings of the 4th International Working Conference on Stored-Product Protection. Tel Aviv, Israel, September 1986. 194-207.

Ripp, B. E., Banks, H. J., Bond, E. J., Calverley, D. J., Jay, E.G., and Navarro, S. (1984) Modified Atmosphere and Fumigation in Grain Storages. Amsterdam, Elsevier. 798

Ronai, K. S. and Jay, E. (1982) Experimental studies on using carbon dioxide to replace conventional fumigants in bulk flour shipments. Association of Operative Millers - Bulletin, 3954-3958.

Sharp, A. K. and Banks, H. J. (1980) Disinfestation of stored durable foodstuffs in freight containers using carbon dioxide generated from dry ice. First International Conference on Technology for Development, 310-314.

Shejbal, J. (1980) Modified atmosphere storage of grains. Developments in Agricultural Engineering, Elsevier, Amsterdam, 608 pp.

Stahl, E., Rau, G. and Adolphi, H. (1985) Entwesung von Drogen durch Kohlendioxid-Druckbehandlung (PEX-Verfahren). Pharm. Ind. 47, 528-530.

Storey, C. L. (1973) Exothermic inert-atmosphere generators for control of insects in stored wheat. Journal of Economic Entomology, 66, 511-514.

Wilson, A. D. Banks, H. J. Annis, P. C. and Guiffre, V. (1980) Pilot commercial treatment of bulk wheat with CO₂ for insect control: the need for gas recirculation. Australian Journal of Experimental Agriculture and Animal Husbandry, 20,618-624.