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Fumigation trials with a mixture of methyl bromide and carbon dioxide in vertical bins
J. stored Prod. Res., 1973, Vol. 8, pp. 315-321.
Pergamon Press. Printed in Great Britain.
Fumigation Trials with a Mixture of Methyl Bromide and Carbon Dioxide in Vertical Bins M. Stored
CALDERON
Products
and Y. CARMI
Research
Laboratory,
(First received 5 May 1972, and injrral
Jaffa,
Israel
form 12 Jme 1972)
Abstract-The efficacy of a fumigant mixture containing methyl bromide and carbon dioxide was examined using the gravity penetration method in vertical bins of wheat. When applied as the mixture methyl bromide penetrated to the bottom of the bins and complete control of test insects at the base of the bins as well as the existing natural infestation was obtained. Methyl bromide applied alone under similar conditions was not detected at the bottom of the bins and the insects of the natural infestation, and test insects remained alive. It is assumed the carbon dioxide acted as a carrier and facilitated the penetration of the methyl bromide to the depth of 17 m through the grain bulk. INTRODUCTION
IN THE search for substitutes to ‘Calandrex’ (64% trichloro-ethylene, ‘26% carbon disulphide, 10% carbon tetrachloride), a fumigant mixture used in Israel, it was decided to examine the use of a fumigant mixture consisting of methyl bromide and carbon dioxide. Carbon dioxide is known to increase insect susceptibility to fumigants (ALINIAZEE and LINDGREN, 1969)) to prevent fire hazards when mixed with flammable materials (MONRO, 1969), and to be lethal to insects at high concentrations (HAREIN and PRESS, 1968). Its ability to penetrate the grain bulk is excellent, probably because absorption by the grain is very low. Methyl bromide, on the other hand, is known to be a very efficient fumigant but its use in silo bins is limited because of unsatisfactory distribution of the gas in the grain bulk (BROWN and HESELTINE, 1949). With the above characteristics in mind the two materials were combined to obtain the advantage of the high insect toxicity of methyl bromide and the high penetrating power of CO,. FUMIGATION
Material
OF
TWO
BINS
AT
REHOVOT
and methods
The trial was carried out at the ‘Shefa-on’ silos in concrete vertical bins 17 m high, 4 -20 m dia and each of 240 rn3 capacity. The bins contained an Israeli selected strain of Mexican wheat of lo-10 *5 per cent moisture content and within a temperature range of 20-24X. 315
316
M.
CALDERON and Y. CARMI
Bin 1 was treated with the MeBr + CO, mixture at a dose of 50 g/m3 MeBr and 250 g/m3 dry ice. Bin 2 was fumigated with MeBr only at a dose of 50 g/m”. All the openings of the bin except for the upper one were sealed. The blocks of dry ice were scattered over the surface of the grain, the upper opening was then sealed and the methyl bromide was applied from a cylinder connected by a tube to a garden sprinkler which was positioned centrally on the surface of the grain. The pressure developed by the MeBr in the cylinder set the sprinkler in motion, thus giving a more uniform distribution of the fumigant ( CALDERON and CARMI, 1969). Dry ice is marketed locally in blocks of 1-2 kg. The blocks were always purchased just before fumigation in order to minimize weight losses by sublimation. Checks of weight before and after transportation of the dry ice showed that loss of weight was negligible provided the blocks were closely packed and well wrapped. One kg dry ice releases 550 1. of CO, gas at 20°C. The fumigated bins remained sealed for 5 days. Samples were drawn through polyethylene tubes (4 mm i.d.) previously inserted to depths of 1 and 17 m from the grain surface in both bins, and also to 14 m in Bin 1. The CO, concentrations were measured by an Orsat apparatus. MeBr concentrations were measured by the Volhard method. Insect mortality was determined by examining the natural insect infestation in 1 kg wheat samples taken from the top and the base of the bin before and after the fumigation, and also by the insertion of cages, each containing 30 adults of Tribolium castuneum (Herbst.) (15-20 days old) and 1 g of bran and flour mixture. The cages were placed in the same positions as the gas sampling points. Results The estimated concentration time (CT) products of MeBr measured during the fumigation of the two bins are given in Figs. 1 and 2, and the concentrations of CO, are given in Table 1.
40ct.
products
g/m3per Im
co
hr
1890
14m
x----x
400
,7m
l . . . . . . . . .. . l
570
“E \ Cn
24
48
72
96
120
hr
FIG. 1. Concentration application
of methyl bromide in the grain mass at various intervals after in Bin 1 ‘Shefa-on’ silos. CT products calculated from these graphs are also shown.
317
Fumigation Trials in Vertical Bins
ct products g/m3per Im-
hr
2480
Bottom
0
hr
FIG. 2. Concentration of methyl bromide in the grain mass at various intervals after application in Bin 2 ‘Shefa-on’ silos. CT products calculated from these graphs are also shown.
From Figs. 1 and 2 it can be seen that high CT products of MeBr were the upper regions of both bins, while CT products at the bottom of the were obtained only when the mixture was used. The MeBr concentrations with time at the bottom of the bins and after 48 hr they could no longer This resulted in lower CT products compared to those at the upper layer TABLE
1. CONCENTRATIONS OF CO, (PER CENT IN INTERGRANULAR FUMIGATION OF BIN 1 AT ‘SHEFA-ON'SILOS
obtained in treated bins decreased be detected. of the grain.
AIR SPACE) DURING
Depth
2 hr
24 hr
Time 48 hr
4 days
5 days
Im 14 m 17 m
22 -4 0.0 0.0
11.6 12.9 18.8
5-o 0.0 0.0
2.0 0.0 0.0
I-O 0.0 0.0
The disappearance of the gas at the bottom of the bin was recorded also with CO, (Table 1). Th e 1ower CT products of both gases can be explained by leakage at the bottom of the bin. In the bin treated with MeBr + CO, mixture a complete mortality of all test insects was obtained in the cages placed at the top and at the base of the bin. In the bin treated only with MeBr a similar effect was obtained in the cages placed in the top layer of the grain, while all insects in the cages placed at the base of the bin remained alive. S.P.R.
s/4-P
M. CALDERON and Y. CARMI
318 TABLE
2. EFFECT OF FUMIGATION ON NATURAL
INFESTATION (I
Bin 2 (MeBr only) Before fumigation After fumigation Live Dead Live Dead
Bin 1 (MeBr + CO,) Before fumigation After fumigation Live Dead Live Dead Upper
surface
> 1000
-
T+S > 1000 G
Bottom
-
T-Tribolium castaneum (Herbst.) S-Sitophilw oryzae (L.) (adults) G- Trogoderma granarium Everts.
kg SAMPLES) IN BINS AT ‘SHEFA-ON’
-
> 1000
> 1000
-
T+S > 1000 G
T+S > 1000
-
-
> 1000
> 1000
> 1000
T+S > 1000
T+S
T+S
T+S
T+S
(adults) (Larvae)
The natural insect infestation in the two bins was very heavy. From the results given in Table 2, it can be seen that for the natural infestation also, complete mortality was obtained only in the bin treated with the MeBr + CO, mixture.
FUMIGATION
Material
OF
TWO
BINS
AT
BRURIM
and methods
In this trial at the ‘Hazera’ silos, two concrete vertical bins 20 m high, 5 m dia, and each of 400 m3 capacity were fumigated. The bins contained wheat, variety semi-dwarf ‘Hazera 2 152’ of 10 ‘5% m.c. and within a temperature range of 23-25X. The fumigation procedure and the methods of recording the results were the same as in the previously described trial except that the gas sampling tubes and the cages too
ct. products g/rr?per hr
80
Im 70
4m Eloitom
n E \ CA
5 6 u
1
2480
w---x . ... .
1840
.......
II00
60 50 40 30 20 IO 0 hr
FIG. 3. Concentration application
of methyl
in Bin 1 ‘Hazera’
bromide
silos. CT
in the grain
products shown.
mass at various
calculated
intervals
from these graphs
after
are also
Fumigation Trials in Vertical Bins
319
ct
6
s0
‘\
40
products
g/m3
\ \ \ \
Im
^
4m
x-----x
per hr
960 1820
Bottom
0
\ 30
\ \
2
24
48
72
96
hr
FIG. 4. Concentration of methyl bromide in the g-rain mass at various intervals after application in Bin 2 ‘Hazera’ silos. CT products calculated from these graphs are also shown.
containing test insects were placed at depths of 1, 4 and 17 m, in the grain bulk of both bins. The fumigation period lasted 4 days. Results
The estimated concentration time products of MeBr in the two bins are given in Figs. 3 and 4, and the CO, concentrations are given in Table 3. The results of this experiment were similar to those of the previous one. Thus, MeBr gas penetrated down to 17 m only when mixed with CO,. In this case high CTproduct values were also obtained at the base of the bin due to the good sealage which prevented leakage. This, as seen in Table 3, resulted in higher concentrations of CO, at the bottom of the bin than at the top, being maintained from 24 hr after introduction till the end of the fumigation period. TABLE
3.
SPACE)
DURING
CONCENTRATIONS FUMIGATION
OF
CO,
(PER CENT
IN INTERGRANULAR
OF A BIN IN ‘HAZERA'
SILO WITH
AIR
MeBr +
co, Time Depth
2 hr
24 hr
48 hr
4 days
lm 4m 17 m
27-O 4-2 0.0
10.4 19.0 19.4
3.6 6.0 13-4
0.8 2.4 4.6
320
M. CALDERONand Y. CARMI
Complete mortality of test insects was obtained in the cages placed at the top and bottom of the bin treated with the MeBr + CO, mixture. In the bin treated with MeBr only, 100 per cent kill was achieved only in the cages in the top layer. In the samples of wheat taken before and after the fumigation no natural insect infestation was found.
DISCUSSION
Methyl bromide is an advantageous fumigant for the fumigation of bulk grain mainly because of the low residue levels remaining after treatment. However, the use of this fumigant in vertical bins is generally limited to those equipped with recirculation systems due to its limited penetration. JOFFE and NOLTE. (1957) used MeBr successfully for fumigation of bulk maize by applying the fumigant to the grain surface, though the grain depth was only 5 m. The main finding in our trials is that the MeBr gas when mixed with CO, applied at the grain surface can penetrate to the bottom of high vertical bins containing wheat, whereas when MeBr is applied alone penetration is limited. We assume that the penetration of MeBr down to at least 17 m through the mass of wheat is due to the CO, which acts as a carrier of the MeBr. The MeBr when applied as the mixture probably reached the depth of 20 m (the height of the fumigated bin) but this could not be demonstrated since gas sampling tubes and cages with test insects could not be inserted at this point. Insect mortality results reflected the gas concentrations recorded in the bulk. Thus, complete mortality was found only in the bins where MeBr penetrated to the bottom. The results of this study may have important applications in commercial fumigations by the gravity penetration method. Carbon tetrachloride is an important component in many commercial fumigation mixtures for fumigation by the gravity method, because of its excellent penetrating properties. However, there is a tendency today to minimize the use of this fumigant because of its potential health risk in form of residues in grain. It can be detected a considerable time after treatment (FAO/WHO MEETING, 1965; BIELORA~ and ALUMOT, 1966). The difficulty in finding a suitable substitute for carbon tetrachloride with similar penetrating properties limits the choice of composition of fumigants mixtures for treating vertical bins. The MeBr + CO, mixture may provide a solution to this problem.
REFERENCES ALINAIZEE, M. T. and LINDGREN,D. L. (1969) Effect of CO, on toxicity of HCN and MeBr to adults of the confused flour beetle and granary weevil at two different temperatures. J.ccon. Ent. 62,904--906. BIELORAI,R. and ALUMOT,E. (1966) Determination of residues of a fumigant mixture in cereal grain by electron-capture gas chromatography. J.A&c. Fd Chem. 14,622-625. BROWN,W. B. and HESELTINE,H. K. (1949) Fumigation of grain in silo bins. Milling, 112,229-230, 233. CALDERON, M. and CARMI,Y. (1969) A simple sprinkling apparatus for fumigation of grain bins by gravity penetration. Progress Report of the Stored Products Research Lab. 1968/g. pp. 43. FAO/WORLD HEALTH ORGANIZATION (1965) Evaluation of the hazards to consumers resulting from the use of fumigants in the protection of food. Rome FAO Meeting Report No p1/1965/10/2 WHO/ Food Add/28 65.
Fumigation Trials in Vertical Bins
321
HAREIN, P. K. and PRESS, A. F. (1968) Mortality of stored peanut insects exposed to mixtures of atmospheric gases at various temperatures. J. stored Prod. Res. 4, 77-82. JOFFE, A. and NOLTE, M. C. A. (1957) Methyl bromide fumigation of horizontally stored bulk maize. J. ent. Sot. S. Afr. 20, 144-153. JONES, R. M. (1938) Toxicity of fumigant CO, mixtures to the red flour beetle. J. econ. Ent. 28,926 933. MONRO,H. A. U. (1969) Manual offumigation for insect control. F.A.O. Agricultural Studies No. 79.
Pergamon Press. Printed in Great Britain.
Fumigation Trials with a Mixture of Methyl Bromide and Carbon Dioxide in Vertical Bins M. Stored
CALDERON
Products
and Y. CARMI
Research
Laboratory,
(First received 5 May 1972, and injrral
Jaffa,
Israel
form 12 Jme 1972)
Abstract-The efficacy of a fumigant mixture containing methyl bromide and carbon dioxide was examined using the gravity penetration method in vertical bins of wheat. When applied as the mixture methyl bromide penetrated to the bottom of the bins and complete control of test insects at the base of the bins as well as the existing natural infestation was obtained. Methyl bromide applied alone under similar conditions was not detected at the bottom of the bins and the insects of the natural infestation, and test insects remained alive. It is assumed the carbon dioxide acted as a carrier and facilitated the penetration of the methyl bromide to the depth of 17 m through the grain bulk. INTRODUCTION
IN THE search for substitutes to ‘Calandrex’ (64% trichloro-ethylene, ‘26% carbon disulphide, 10% carbon tetrachloride), a fumigant mixture used in Israel, it was decided to examine the use of a fumigant mixture consisting of methyl bromide and carbon dioxide. Carbon dioxide is known to increase insect susceptibility to fumigants (ALINIAZEE and LINDGREN, 1969)) to prevent fire hazards when mixed with flammable materials (MONRO, 1969), and to be lethal to insects at high concentrations (HAREIN and PRESS, 1968). Its ability to penetrate the grain bulk is excellent, probably because absorption by the grain is very low. Methyl bromide, on the other hand, is known to be a very efficient fumigant but its use in silo bins is limited because of unsatisfactory distribution of the gas in the grain bulk (BROWN and HESELTINE, 1949). With the above characteristics in mind the two materials were combined to obtain the advantage of the high insect toxicity of methyl bromide and the high penetrating power of CO,. FUMIGATION
Material
OF
TWO
BINS
AT
REHOVOT
and methods
The trial was carried out at the ‘Shefa-on’ silos in concrete vertical bins 17 m high, 4 -20 m dia and each of 240 rn3 capacity. The bins contained an Israeli selected strain of Mexican wheat of lo-10 *5 per cent moisture content and within a temperature range of 20-24X. 315
316
M.
CALDERON and Y. CARMI
Bin 1 was treated with the MeBr + CO, mixture at a dose of 50 g/m3 MeBr and 250 g/m3 dry ice. Bin 2 was fumigated with MeBr only at a dose of 50 g/m”. All the openings of the bin except for the upper one were sealed. The blocks of dry ice were scattered over the surface of the grain, the upper opening was then sealed and the methyl bromide was applied from a cylinder connected by a tube to a garden sprinkler which was positioned centrally on the surface of the grain. The pressure developed by the MeBr in the cylinder set the sprinkler in motion, thus giving a more uniform distribution of the fumigant ( CALDERON and CARMI, 1969). Dry ice is marketed locally in blocks of 1-2 kg. The blocks were always purchased just before fumigation in order to minimize weight losses by sublimation. Checks of weight before and after transportation of the dry ice showed that loss of weight was negligible provided the blocks were closely packed and well wrapped. One kg dry ice releases 550 1. of CO, gas at 20°C. The fumigated bins remained sealed for 5 days. Samples were drawn through polyethylene tubes (4 mm i.d.) previously inserted to depths of 1 and 17 m from the grain surface in both bins, and also to 14 m in Bin 1. The CO, concentrations were measured by an Orsat apparatus. MeBr concentrations were measured by the Volhard method. Insect mortality was determined by examining the natural insect infestation in 1 kg wheat samples taken from the top and the base of the bin before and after the fumigation, and also by the insertion of cages, each containing 30 adults of Tribolium castuneum (Herbst.) (15-20 days old) and 1 g of bran and flour mixture. The cages were placed in the same positions as the gas sampling points. Results The estimated concentration time (CT) products of MeBr measured during the fumigation of the two bins are given in Figs. 1 and 2, and the concentrations of CO, are given in Table 1.
40ct.
products
g/m3per Im
co
hr
1890
14m
x----x
400
,7m
l . . . . . . . . .. . l
570
“E \ Cn
24
48
72
96
120
hr
FIG. 1. Concentration application
of methyl bromide in the grain mass at various intervals after in Bin 1 ‘Shefa-on’ silos. CT products calculated from these graphs are also shown.
317
Fumigation Trials in Vertical Bins
ct products g/m3per Im-
hr
2480
Bottom
0
hr
FIG. 2. Concentration of methyl bromide in the grain mass at various intervals after application in Bin 2 ‘Shefa-on’ silos. CT products calculated from these graphs are also shown.
From Figs. 1 and 2 it can be seen that high CT products of MeBr were the upper regions of both bins, while CT products at the bottom of the were obtained only when the mixture was used. The MeBr concentrations with time at the bottom of the bins and after 48 hr they could no longer This resulted in lower CT products compared to those at the upper layer TABLE
1. CONCENTRATIONS OF CO, (PER CENT IN INTERGRANULAR FUMIGATION OF BIN 1 AT ‘SHEFA-ON'SILOS
obtained in treated bins decreased be detected. of the grain.
AIR SPACE) DURING
Depth
2 hr
24 hr
Time 48 hr
4 days
5 days
Im 14 m 17 m
22 -4 0.0 0.0
11.6 12.9 18.8
5-o 0.0 0.0
2.0 0.0 0.0
I-O 0.0 0.0
The disappearance of the gas at the bottom of the bin was recorded also with CO, (Table 1). Th e 1ower CT products of both gases can be explained by leakage at the bottom of the bin. In the bin treated with MeBr + CO, mixture a complete mortality of all test insects was obtained in the cages placed at the top and at the base of the bin. In the bin treated only with MeBr a similar effect was obtained in the cages placed in the top layer of the grain, while all insects in the cages placed at the base of the bin remained alive. S.P.R.
s/4-P
M. CALDERON and Y. CARMI
318 TABLE
2. EFFECT OF FUMIGATION ON NATURAL
INFESTATION (I
Bin 2 (MeBr only) Before fumigation After fumigation Live Dead Live Dead
Bin 1 (MeBr + CO,) Before fumigation After fumigation Live Dead Live Dead Upper
surface
> 1000
-
T+S > 1000 G
Bottom
-
T-Tribolium castaneum (Herbst.) S-Sitophilw oryzae (L.) (adults) G- Trogoderma granarium Everts.
kg SAMPLES) IN BINS AT ‘SHEFA-ON’
-
> 1000
> 1000
-
T+S > 1000 G
T+S > 1000
-
-
> 1000
> 1000
> 1000
T+S > 1000
T+S
T+S
T+S
T+S
(adults) (Larvae)
The natural insect infestation in the two bins was very heavy. From the results given in Table 2, it can be seen that for the natural infestation also, complete mortality was obtained only in the bin treated with the MeBr + CO, mixture.
FUMIGATION
Material
OF
TWO
BINS
AT
BRURIM
and methods
In this trial at the ‘Hazera’ silos, two concrete vertical bins 20 m high, 5 m dia, and each of 400 m3 capacity were fumigated. The bins contained wheat, variety semi-dwarf ‘Hazera 2 152’ of 10 ‘5% m.c. and within a temperature range of 23-25X. The fumigation procedure and the methods of recording the results were the same as in the previously described trial except that the gas sampling tubes and the cages too
ct. products g/rr?per hr
80
Im 70
4m Eloitom
n E \ CA
5 6 u
1
2480
w---x . ... .
1840
.......
II00
60 50 40 30 20 IO 0 hr
FIG. 3. Concentration application
of methyl
in Bin 1 ‘Hazera’
bromide
silos. CT
in the grain
products shown.
mass at various
calculated
intervals
from these graphs
after
are also
Fumigation Trials in Vertical Bins
319
ct
6
s0
‘\
40
products
g/m3
\ \ \ \
Im
^
4m
x-----x
per hr
960 1820
Bottom
0
\ 30
\ \
2
24
48
72
96
hr
FIG. 4. Concentration of methyl bromide in the g-rain mass at various intervals after application in Bin 2 ‘Hazera’ silos. CT products calculated from these graphs are also shown.
containing test insects were placed at depths of 1, 4 and 17 m, in the grain bulk of both bins. The fumigation period lasted 4 days. Results
The estimated concentration time products of MeBr in the two bins are given in Figs. 3 and 4, and the CO, concentrations are given in Table 3. The results of this experiment were similar to those of the previous one. Thus, MeBr gas penetrated down to 17 m only when mixed with CO,. In this case high CTproduct values were also obtained at the base of the bin due to the good sealage which prevented leakage. This, as seen in Table 3, resulted in higher concentrations of CO, at the bottom of the bin than at the top, being maintained from 24 hr after introduction till the end of the fumigation period. TABLE
3.
SPACE)
DURING
CONCENTRATIONS FUMIGATION
OF
CO,
(PER CENT
IN INTERGRANULAR
OF A BIN IN ‘HAZERA'
SILO WITH
AIR
MeBr +
co, Time Depth
2 hr
24 hr
48 hr
4 days
lm 4m 17 m
27-O 4-2 0.0
10.4 19.0 19.4
3.6 6.0 13-4
0.8 2.4 4.6
320
M. CALDERONand Y. CARMI
Complete mortality of test insects was obtained in the cages placed at the top and bottom of the bin treated with the MeBr + CO, mixture. In the bin treated with MeBr only, 100 per cent kill was achieved only in the cages in the top layer. In the samples of wheat taken before and after the fumigation no natural insect infestation was found.
DISCUSSION
Methyl bromide is an advantageous fumigant for the fumigation of bulk grain mainly because of the low residue levels remaining after treatment. However, the use of this fumigant in vertical bins is generally limited to those equipped with recirculation systems due to its limited penetration. JOFFE and NOLTE. (1957) used MeBr successfully for fumigation of bulk maize by applying the fumigant to the grain surface, though the grain depth was only 5 m. The main finding in our trials is that the MeBr gas when mixed with CO, applied at the grain surface can penetrate to the bottom of high vertical bins containing wheat, whereas when MeBr is applied alone penetration is limited. We assume that the penetration of MeBr down to at least 17 m through the mass of wheat is due to the CO, which acts as a carrier of the MeBr. The MeBr when applied as the mixture probably reached the depth of 20 m (the height of the fumigated bin) but this could not be demonstrated since gas sampling tubes and cages with test insects could not be inserted at this point. Insect mortality results reflected the gas concentrations recorded in the bulk. Thus, complete mortality was found only in the bins where MeBr penetrated to the bottom. The results of this study may have important applications in commercial fumigations by the gravity penetration method. Carbon tetrachloride is an important component in many commercial fumigation mixtures for fumigation by the gravity method, because of its excellent penetrating properties. However, there is a tendency today to minimize the use of this fumigant because of its potential health risk in form of residues in grain. It can be detected a considerable time after treatment (FAO/WHO MEETING, 1965; BIELORA~ and ALUMOT, 1966). The difficulty in finding a suitable substitute for carbon tetrachloride with similar penetrating properties limits the choice of composition of fumigants mixtures for treating vertical bins. The MeBr + CO, mixture may provide a solution to this problem.
REFERENCES ALINAIZEE, M. T. and LINDGREN,D. L. (1969) Effect of CO, on toxicity of HCN and MeBr to adults of the confused flour beetle and granary weevil at two different temperatures. J.ccon. Ent. 62,904--906. BIELORAI,R. and ALUMOT,E. (1966) Determination of residues of a fumigant mixture in cereal grain by electron-capture gas chromatography. J.A&c. Fd Chem. 14,622-625. BROWN,W. B. and HESELTINE,H. K. (1949) Fumigation of grain in silo bins. Milling, 112,229-230, 233. CALDERON, M. and CARMI,Y. (1969) A simple sprinkling apparatus for fumigation of grain bins by gravity penetration. Progress Report of the Stored Products Research Lab. 1968/g. pp. 43. FAO/WORLD HEALTH ORGANIZATION (1965) Evaluation of the hazards to consumers resulting from the use of fumigants in the protection of food. Rome FAO Meeting Report No p1/1965/10/2 WHO/ Food Add/28 65.
Fumigation Trials in Vertical Bins
321
HAREIN, P. K. and PRESS, A. F. (1968) Mortality of stored peanut insects exposed to mixtures of atmospheric gases at various temperatures. J. stored Prod. Res. 4, 77-82. JOFFE, A. and NOLTE, M. C. A. (1957) Methyl bromide fumigation of horizontally stored bulk maize. J. ent. Sot. S. Afr. 20, 144-153. JONES, R. M. (1938) Toxicity of fumigant CO, mixtures to the red flour beetle. J. econ. Ent. 28,926 933. MONRO,H. A. U. (1969) Manual offumigation for insect control. F.A.O. Agricultural Studies No. 79.