Proceedings of the 7th Intematumal Working Conference on Stored-product Protection - Volume 1

Research on carbonyl sulfide as a fumigant for control ofstored grain insects

Tan Xianchang , Hou Xmgwei , Cheng Lizheng and Wu jianchun'

Abstract

Laboratory data showed that carbonyl sulfide (COS) wastOXICto stored gram insects. After 24-h exposure time, thedosages for 100% control of adults were 7.28 mg/L toRhizopertha domnuca (F ) and psocids, 14 5 mg./L toOruzoeptuiue suruuimeruns (L.) and Callosobruchuschinensis (L.), 29 2 mg/L to Sitopiuius oryzae (L ),Sitophslus zeanuus (Motschulsky) , Lasiodermaserricorne (F.), Cryptolestes pusilius (Schonherr),Callosoorucnu» malulaius (F ), Troqoderma ixiruibile(Balhon) and Triboliuni casianeum (Herbst), 44.2 mg/Lto Trtboliurn. confusum (Jacquelm du Val) The mosttolerant stages of T castaneum and T. confusuni werethe eggs and pupa.COSreduced gernunation of maize, soybean, mung bean,

wheat and paddy. The order of damage was maize> soybean> paddy> mung bean> wheat> sorghum> barley COSmight also cause changes m soybean colorCOS had adverse effect on quahty of wheat. Both the

bread made from wheat fumigated with COS at the dosageabove 50 mg/L and the nee made from paddy fumigated atthe dosage above 100 mg/L after 6 months aeration, had anoff odor.COS at 12 - 29% could cause igmtion or explosion by

spark Ignition could be mlubited by addmg CO2half of theCOSvolume.COSm the mtergranular air space decayed quickly, and

could keep 3 - 9 days dunng funugation of gram Dunngaeration, there was an obViOUSsmell of HzS m the gramfumigated With higher concentrations of COS, but no COSresidue could be detected after 1 day aeration.Field trails results showed that wheat and paddy fumigated

WithCOS at a dosage of 50g/m3 and 7 days exposure tunecontrolled the pests in the gram

Introduction

In Chma, stored gram is subject to infestatiOn by more than

1 Chengdu Gram Storage Research Institute, 95 Huapalfang stChengdu, Sichuan proVince, 610031, Chma

200 species of stored gram msect pests. Alummumphosphide is the major compound for dismfestanon of storedgram. More than 95% of stored gram m state warehouseswas fumigated With phosphme each year. Owing to theappearance of resistance of stored gram msect pests tophosphme in Chma (Zeng L 1998), there is an urgent needfor alternatives of phosphme fumigation of stored gram.Carbonyl sulfide is Similar to carbon disulfide and carbon

dioxide, havmg properties between these two compounds Itis a kmd of colorless, odorless and tasteless gas, but whenthe mdustnal products of carbonyl sulfide or pure COS isexposed m the air, a slight odor of hydrogen sulfide will begiven off Desmarcheher (1994) reported that carbonylsulfide may replace methyl bromide and phosphine forfurmgation. It is tOXiCto many of the major stored productmsect pests In the mtergranular air space, carbonyl sulfidedecays more slowly than methyl bromide. It has no adverseeffect on the germmation of wheat Zettler et al. (1997)reported the toxicity of carbonyl sulfide to 5 species ofstored product msects and considered it has the potential useas a fumigant of dned fruits and nutsThis paper summanzed the mam results of laboratory

expenments and field tratls of carbonyl sulfide, which werecarried out m Chma for control of stored, gram msect pests.

The Toxicity of Carbonyl Sulfideto Stored Grain Insect Pests

Test msects have been reared in laboratory on standard dietsat 28°C and 70% r. h for several years. The test msectswere Rhizoperiha domrnica (F), Oruaiephilu»surnuimensis (L.), Callosobruchus chinensis (L.) ,Suophiiu» oryzae (L), Sitophilus zeamuus( Motschulsky ), Las uxle t'ma serriconl,e (F. ),Cryptolestes puszllus (Schonherr), Callosobruchusmaculatus (F) , Trogoderma varwbl,le (Balhon) ,Tnbol mm castaneum (Herbst), Tnbol ium confusum(Jacquehn du Val) and Psocid (a speCiesof Ll,poscehdae).Zhuzhou PestICide Factory, Hunan Provmce prOVided

mdustnal product of carbonyl sulfide Its punty was higherthan 99% , and it was stored m a steel camster for storage ofhquefied petroleum gasBiOassayswere conducted m 500 ml fumigatIon bottles

With ground glass valve, a rubber tube was fitted between

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Proceedmqs of the 7th Internaiumal Working Conference on Stored-product Protection. - Volume 1

the valve and a vacuum pump. Required concentrations of exposure time, apart from specially mentioned ones, insectscarbonyl sulfide were introduced by reducing pressure, and were put m wheat for 7 days, then mortality was assessedthe system was equilibrated to atmosphere pressure after and adjusted according to Abbott's formula. Results werecarbonyl sulfide was introduced Assays were performed m discarded when control mortality exceeded 10%.triplicate, With 30 or 50 msects at 28°C. After 24-hours

Table 1. Toxicity of carbonyl sulfide to major insects of stored grain.

Mortality (% )1(5. D.)

Insects Concentration of carbonyl sulfide (rng/L)

1.45 2.91 7.28 14.5 29.2 43.7 72.8

R. donunLCa(adults)2 94.6(4.1) 98.6(2.3) 100 100 100 100 100

Psocids' 0 80.5(5.6) 100 100 100 100 100

O. sunnarnensis(adults) 0.7 1.3 98.6(1.2) 100 100 100 100

C. chinensis (adults)? 0 0 85.4(2.9) 100 100 100 100

S.oryzae(adults) 12.6(1.5) 9.6(0.6) 28.4(10.5) 97.5(2.3) 100 100 100

S. zeamais(adults) 1.3 1.6(0.6) 0 44.5(10 .5) 100 100 100

L .serricorne (adults)? 7.8(5.0) 27.1(3.5) 64.3(2.1) 84.6(1.7) 100 100 100

C. pusillus (adults) 0.51 0.41 10.5(5.3) 98.7(2.0) 100 100 100

C. maculatus (adults) 9.7 13.8(1.7) 21.8(5.7) 89.7(8,3) 100 100 100

T. variabtle(adults) 0 1.5 31.5(14.1) 86.6(11.5) 100 100 100

(larvae) 0 0 0 85.0(9.0) 100 100 100

T castaneum. (adults) 0 2.7(3.8) 22.0(11.0) 98.7(2.6) 100 100 100

(pupae) 0 0 0 4.2(5.3) 100 100 100

(larvae) 1.1 1.1 17.9(0.4) 56.6(12.3) 100 100 100

(eggs) 6.4(3.4) 1.3(0.9) 6.5(2.0) 31.0(4.7) 100 100 100

T. confusum. (adults) 0 0 0 97.9(1.1) 99.3(1.2) 100 100

(pupae) 0 0 0 28.2(12.7) 100 100 100

(larvae) 0 0 0 58.9(11.6) 100 100 100

(eggs) 0 0 2.4(1.0) 0.1 25.6(18.0) 98.7(4.6) 100

1 exposure 24 hr , temperature 28t:2 mortality assessed at 24 hr after dosmg

Adults of R dominuxi and Psocid were the mostsusceptible to carbonyl sulfrde, as 7. 28mgIL concentrationgave 100% mortality (Table O. O. euruusmensis and C.chinensis were less susceptible as 14. 5mgIL gave 100 %mortality. For 100% control of S oruzae , S. zeamais ,L. sericorne , C. pusills , C. maculaius , T. uiruibileand T. castaneum 29. 2mgIL was needed. T. confusumiwas tolerant to carbony 1 sulfide, having 100% mortalityonly at 44. 2mgIL T. castoneum. and T. confusum. eggsand pupae were more tolerant to carbonyl sulfide than larvaeand adults. The eggs of T confusum. were the mosttolerant stage. Desmarcheher (1994) also found that themost susceptible species tested were adult Psocid and adultR. dominica Zettler et al. (1997) also indicated that theegg and pupa stages of T confusum. were the leastsusceptible to carbonyl sulfide.

According to the above results, It could be considered thata dosage of 30mgIL and one day exposure time are enough tocontrol the most insects tested, but It needs either a higherdosage or a longer exposure time for the control of the eggsof T confusum.

The Effect of CarbonylSulfide on Seed Germination

Seeds of wheat, paddy, maize, sorghum, barley, soybeanand mung bean were placed m 500ml bottle and furrugatedfor 7 days at the dosages of 0, 25, 50, 100, 250 and500mgIL at 30°C and aerated for 7 days. Germmation wastested by standard method There were 4 replicates for eachtreatment.

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Proceedings of the 7th International Worhng Conference on Stored-product Protection. - Volume 1

Table 2. Effect of carbonyl sulfide on the gemuna non rate of seed (% ) .

Concentration of carbonyl sulfide (rng/L)

Seed 0 25 50 100 250 500

Wheat 98.5 95.0 92.3 81.0 79 8 78.0

Paddy 95.3 92.3 89.8 36.8 76.1 91.8

Maize 96.6 77.5 79.0 60.0 28.2 13.4Sorghum 62.5 59.8 60.2 57.3 70.2 64.8

Barley 24.0 55.0 63.3 59.5 79.8 81.0

Soybean 95.5 92.0 90.3 91.3 27.3 54.0

Mung bean 90.8 88.0 89.3 78.5 61.0 50.0

Among the 7 tested seeds, the germmation of soybean,mung bean and wheat decreased when the dosage increased(Table 2). Soybean color changed from yellow to greenafter fumigation and as the dosage mcreased, the colorchange increased The paddy seeds showed the lowestdegree of germmation at 100mgIL among testedconcentrations. It seemed that the change of carbonylsulfide concentration had no adverse effect on sorghumgermmation, and on the contrary, the mcrease of carbonylsulfide concentration tended to have a positive effect onbarley gernunation. The results of wheat (Table 2) wereunlike that showed by Desmarcheher (1994) as carbonylsulfide had no adverse effect on the germmation of wheat.Maybe there were no higher dosage treatments in hisexpenments Accordmg to the results of this paper, it couldbe recognized that except for sorghum and barley, the testedspecies of seeds should not be treated by carbonyl sulfidefurmga tion in practice.

The Effect of Carbonyl Sulfide onQuality of Wheat and Paddy

Each treatment of 1kg wheat or paddy was fumigated with

carbonyl sulfide at the dosage of 0 g/rn", 50 g/rn", 100 g/rrr' or 200 g/rrr' separately m fumigation bottle at 100%packmg rate at 30°C. After 7 days exposure and 187 daysaeration m enamel tray at room temperature, the wheat wasnulled With Brabender null. The obtamed flour was used fordetermma tion of properties of dough by the Bradenderfarnograph and Brabender extensograph and for makmgbread and steam bread for taste test Paddy was milled after180 days aeration, the nee obtamed was used fordetermmation of the water absorption of nee, expansion andiodine-blue value of cooking nee, and dry substance m neecookmg water and the taste test of cooked nee.Carbonyl sulfide fumigation at all dosage rate reduced

flour quahty (Table 3) It reduced the consistency ofdough, curve area of extensogram and the volume of bread.At the highest concentration. It also gave an unpleasantflavor to bread and steam bread even after 180 daysaeration Carbonyl sulfide had no obvious adverse effect onthe water absorption of nee, expansion of cooking rice,iodine- blue of cookmg nee and dry substance m rice cookmgwater, but It could also bring an unpleasant flavor to cookednee If the fumigation dosage was higher than 100 g/rrr'.

Table 3. Effect of carbonyl sulfide fumigation on quality of wheat flour.

Dosage (g/m")

Test 0 50 100 200

Test using fannnograph Developmg time (nun) 1.2 1.2 1.2 1.2

Stability time (mm) 3.1 2.8 2.8 2.8

Degree of softenmg (F U 105 110 100 105

Test usmg extensograph Extensibility (ern) 14.3 14.8 14.9 14.9

Consistency (B. U ) 300 255 255 240

Curve area (em") 66.8 61.6 59.2 56.2

Bread test Volume (rnl) 568 547 553 522

Unpleasant flavor No No NO ObVIOUS

Steam bread test after 1 day aeration Volume (rnl) 335 347 350 348

Unpleasant flavor No Slight Slight Obvious

Steam bread test after half a year aeration Unpleasant flavor No No No Slight

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Proceedmqe of the 7th International Worhng Conference on Stored-product Protection - Yoiume 1

A 6 6, ........,'A ................6. 6., ........" ............, ........

" A A ~ <..c., ...., ........, ........, ........, ...."""",,-~_~~~ ...... __ .-...._-.... ~~ __ ....6.. b. ~

40 50 60

Research on the Safety ofCarbonyl Sulfide

Carbonyl sulfide IS a kmd of flammable gas If It IS used as afumigant for stored gram funugation, Its flammability andthe safety measure should be studied,The expenments were conducted m PVC film sachets With

a pipe for mtroducmg the gas. A pair of electrodes wasmstalled in the sachet for producmg electric spark. A seriesof gas mixtures at different concentrations m the air,carbonyl sulfide and carbon dioxide were added to thesebags. Then ignited It by an induction coil, Its combustion or

COS CO2

(VV)

I 05

04

1 02

I 0

5 10 15 20

COS III arr % ( v I v ) ( A flammable 6 not flammable)

25 30

explosion was observed. The results are Illustrated m figure1 In figure, The flammable region was inside the trianglearea, outside of which was the safe region. The flammabilitygas concentration range of smgle carbonyl sulfide m the airwas 12 - 29% and outside tlus range the gas mixture wasnot flammable. ThIS data IS very similar to the data of Saxand leWIS (1989). The myroducyion of carbon dIOXIde tothe mixture of carbonyl sulfide and air reduced theflammabihty of the gas mixture. When the volume ratio ofcarbonyl sulfide: carbon dIOXIdewas equal to 1 0.5, the gasmixture was not flammable ThIS result gives a possibility toensure the safety when carbonyl sulfide IS used as a fumigantfor stored gram fumigation.

Fig. 1. Flammable region of gas mixture of carbonyl sulfide, arr and carbon dioxide

Sorption of CarbonylSulfide in Grain Fumigation

Wheat, paddy and maize were fumigated m 500mlfumigation bottles at a 90% packmg rate at 30°C and dosageof carbonyl sulfide was 100g/m3• After dosmg, gas sampleswere taken out by syrmge at different times Theconcentration of carbonyl sulfide was analyzed by gaschromatography WIth flame photometnc detector (sulfurfilter}, column 4m x 3.2 mm, front 2m packed WIth 30%dioctyl phthalate on Shimahte , other 2m packed With 25 %polythylene glycol 600 on Shima lite , column temperature60°C.

Results showed that, carbonyl sulfide m wheat (moisturecontent 13.8 %) decayed rapidly, and 3 days after dosmg,ItS concentration could not be detected. In maize (moisturecontent 13.1 %) It mamtamed 6 days In paddy (rnoisturecontent 12.0%) It decayed slowly as the concentrationlowered nearly to nil at the 9th day. In an empty bottle, thesame dosage of carbonyl sulfIde was added at the begmmngtime of the first 5 days, the concentration reduced from100 % to about 35 %, but durmg the 5 - 15th days itsconcentratIOn lowered to less than 5%. These results could

be explained that decompositron of carbonyl sulfide wasclosely relative to the moisture content of environment.Carbonyl sulfide under m water vapor hydrolyzes to carbondIOXIdeand hydrogen sulfide (Ferm 1957). In the emptybottle, carbonyl sulfide reacted WIth the moisture in thebottle, and at the begmnmg It decayed rapidly, but after themoisture was exhausted, It decayed slowly.

Field Trails of Carbonyl SulfideFumigation to Control Insect

Pests of Stored Grain

FIeld tnals were conducted in No 27 Warehouse ofMongyong Grain Station of Pengzhou City m June, 1996.250kg of wheat or paddy was stored m bamboo mat bins,

covered With PVC plastic film sheets and sealed to theground WIth dry sand. The dosages of carbonyl sulfide wereo g/rrr", 50 g/rrr' and 100 g/m3 respectively. Everytreatment was duplicated. Insects tested were S. zeamuus ,T. confusum and R. donmuca. One hundred adultmsects were placed m nylon net sachets WIth a small amountof broken wheat. Before fUmIgation, the sachets WIthmsects were Just put under the top surface of the gram

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Proceedmas of the 7 th Iniernatumal Working Conference on Stored-product Protectwn - Volume 1

After 7 days exposure, the mortahty of msects wasassessed. After 24hrs, samples were analyzed for COSresidues by gas chromatography The detected lowestconcentration of carbonyl sulfide was 0.005 mglkg, therecovery from wheat was 93.5% and 83.6% from paddyAn exposure time of 7 days at dosages of 50 - 100 g/rrr' IS

Table 4. Results of field trails

enough for controlhng adults of 5 zeamais , T.confueum and R. dominica (Table 4). In experimentsthe lower dosage was 50g/m3, so It could be reduced for thecontrol of these msects m practice There were no COSresidues detected m any of the samples

Grain Dosage (g/m")Mortahty of msects (%) Residue of COS

S. zeamais T confusum R dormmea in gram (rng.vkg)

0 3.2 0.8 3.4

50 100 100 100 Not detected

100 100 100 100 Not detected

0 a a 29

50 100 100 100 Not detected

100 100 100 100 Not detected

Wheat

Paddy

Summary

1. Carbonyl sulfide IS effective to control many species ofstored gram msect pests, among them R. dommica andPsocids are most sensitive.

2. Except sorghum and barley, carbonyl sulfide fumigationcan reduce seed germmation of the other gram tested Italso causes color change m soybean.

3 Carbonyl sulfide fumigation has adverse effect on thequahty of flour and nee. It can bring an unpleasant flavorto the bread and cooked nee, even aerated for half ayear.

4. Explosion of carbonyl sulfide in atr IS not VIOlent. Addmgcarbonyl dIOXIde to the mixture of carbonyl sulfide, aircan mlubrt explosion and ignition of It.

5. Under field condition, carbonyl sulfide fumigation at adosage of 50 g/nr' is effective to control msect pests ofstored gram.

6 There are no COS residues m gram 1 day after the end offumigation.

7. Carbonyl sulfide IS not a good fumigant for controllmg

insect pests of stored gram, but It IS worth studying ItSuse m other fields as a fumigant.

References

Desmarchelier, J. M. 1994 Carbonyl sulphide as a fumigantfor control of insects and mites. Proceedmg of the 6thInternational Workmg Conference on Store-productProtection 1, 78 - 82pFerm, F. J. 1957, The chemistry of carbonyl sulfide,Chemical Reviews, 57, 621 - 640pSax, N.1. and Lewis, R. J. 1989, Dangerous properties ofmdustnal matenals, 7th ed New York, Van NostrandReinhold.Zettler. J. L ; Leech, J. G. ; GIll, R. F and Mackey, B. E.1997 TOXICIty of carbonyl sulfide to stored productinsects. J. Econ Entomol, 90(3): 832 - 836p.Zeng Ling, 1998, Development and countermeasures ofphosphme resistance m stored gram msects m Guangdongof China, presented in the 7th IWCSPP, Beijing, China,October 1998.

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