Bioresource Technology 39 (1992) 229-232 . , e ,

A Study on the Use of Biogas from Cowdung for Storage Insect Control S. Mohan & M. Gopalan*

Department of Agricultural Entomology, Tamil Nadu G.D., Naidu Agricultural University, Coimbatore 641 003, India

(Received 20 December 1990; accepted 16 January 1991 )

Abstract

Biogas from cowdung which comprises mainly 60% methane and 40% carbon dioxide was used as a fumigant in a specially designed air-tight bin of one quintal capacity (100 kg) for the control of a storage insect of pulses, Callosobruchus chinensis L. in seeds and grains of pigeonpea Cajanus cajan L. var. Co-4. Results indicated 100% mortality of eggs, grubs and adults within a period of lO days of fumi- gation. Biogas fumigation did not affect seed germi- nation, seedling vigour or grain quality of pigeonpea. No gaseous methane residues were left in the grain after the fumigation period.

paddy. Hence attempts were made to study in detail and apply the technique of biogas fumiga- tion in pigeonpea (Cajanus cajan L.), the most important leguminous pulse crop of India, for the control of the pulse beetle, Callosobruchus chinensis L.

ME T H O D S

A special type of PVC leak-proof bin of one quintal (100 kg) capacity was developed for bio- gas fumigation. The bin was rectangular in shape

Key words: Biogas, cowdung, storage insect, air tight, Bruchid beetle, fumigation, seed quality, grain quality, pigeonpea.

INTRODUCTION

Fumigation with chemical fumigants like ethylene dibromide and aluminium phosphide for the con- trol of stored-product pests has certain dis- advantages: handling hazards, residual effects and the development of resistance by the insects (Tyler et al., 1983). Though carbon dioxide was effec- tively demonstrated as an alternative fumigant (Lindgren & Vincent, 1920) the availability of carbon dioxide cylinders and other requirements at the farmer's level is difficult. Recently Palani- samy and Dakshinamurthy (1986) demonstrated under laboratory conditions the effectiveness of biogas as a fumigant for control of storage pests of

*To whom cor re spondence should be addressed.

229

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Bioresource Technology 0960-8524/91/S03.50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain

230 S. Mohan, M. Gopalan

with a circular top portion closed with a remov- able air-tight lid (Figs 1-4). The lid was provided with a gasket arrangement in two layers which arrested the leakage of biogas from the bin. The biogas inlet gate valve was fitted at three-quarters height of the bin so that the space below the inlet valve could be filled with pigeonpea seeds and the remaining space at the top would be occupied by biogas. An outlet was provided in the lid to facilitate checking for the presence of biogas.

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One quintal of sound, insect-free, pigeonpea seeds and grains var. Co-4 at a moisture level of 10% (wet basis) were kept in the bin. Pigeonpea seeds and grains with eggs, grubs and adults in perforated plastic containers (2"5 cm diameter and 5-5 cm length) were placed at the bottom, middle and top in the stored-grain bed. There were three replications of the trials. These plastic containers were mounted on a specially designed metal rod with holders. Biogas from a biogas plant (cowdung slurry) at a pressure of 1.4 kg/cm 2 was let into the bin through the inlet value. After checking the release of biogas through the outlet by smelling, the outlet valve was closed. The quan- tity of gas passed into the bin was measured using a flow meter and was found to be 10 litres. Periods of fumigation maintained were 3, 5, 7, 9, 10 and 12 days. After ascertaining the optimum period of fumigation for 100% kill of the insect, sample seeds and grains were taken from the optimum

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Table 1. Percent mortality of pulse beetles in different layers of the seed stored in the biogas fumigation bin

Period of fumigation

(days)

Percent mortality (mean)

Top layer Middle layer Bottom layer

3 26"67 8"00 4"00 (31-11) (16"40) (11"54)

5 26"67 13"33 8"00 (31"11) (21"39) (16"40)

7 100'00 100-00 46.67 (90.00) (90.00) (43.11)

9 100.00 100.00 88.00 (90.00) (90.00) (69.73)

10 100.00 100-00 100.00 (90.00) (90.00) (90.00)

12 100-00 100.00 100.00 (9o.oo) (9o.oo) (9o.oo)

CD Values (P= 0"05 ) 4.70 7"23 6-98

Biogas as insect fumigant 231

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Fig. 5. Percent mortality of eggs, grubs and adults of Callosobruchus chinensis L. during different exposure periods in different layers of the bin.

level and analysed for seed- and grain-cooking quality adopting the method suggested by Abdul- B aki and Anderson (1973). Residues of gaseous methane in the grain after the optimum fumiga- tion period were also qualitatively estimated using gas chromatography.

RESULTS AND DISCUSSION

The percentage kill of eggs, grubs and adults of Callosobruchus chinensis is shown in Fig. 5. There was a significant difference in insect mortality between the different periods of fumiga- tion and for different layers. One hundred percent mortality of eggs, grubs and adults in all the three layers was obtained on the 10th and 12th days of fumigation (Table 1). This indicates that for adequate penetration of the biogas to different layers at the applied pressure of 1.4 kg/cm 2, a minimum period of 10 days is required. The seed

Table 2. Effect of biogas on the seed qualities of Co-4 pigeonpea

Particulars Treated (mean) Cbntrol (mean)

1. Germination (%) 95"38 96.15 2. Vigour index 3092.13 3065.34

CD Values (P = 0"05, non-significant)

Table 3. Cooking qualities of biogas fumigated Co-4 pigeonpea

Qualities Fumigated (mean) Control (mean)

1. Cooking time (min) 32.2 33"0

2. Water uptake 83 83 (g/100 g of sample)

3. Water before and 7.43 7.46 after cooking (100 grain weight (g)) 17.03 16.90

4. Taste and flavour No change No change

232 S. Mohan, M. Gopalan

qualities (Table 2) and grain cooking quality (Table 3) were not affected due to biogas treatment. Analysis for methane in the treated grains did not show any significant residues.

The present investigation is of great sig- nificance in the present context of development of insect resistance and residual problems. As biogas is available on most of the farms of developing countries, the farmers can easily adopt this latest technology to protect their valuable seeds and grains using the bin developed for this purpose.

REFERENCES

Abdul-Baki, A. A. & Anderson, J. D. (1973). Vigour deter- mination in soybean seed by multiple criteria. Crop Sci., 13,630-3.

Lindgren, D. L. & Vincent, L. E. (1920). Effect of atmo- spheric gases alone or in combination on the mortality of gianary and rice weevils. J. Econ. Entomol., 63, 1926-9.

Palanisamy, P. T. & Dakshinamurthy, A. (1986). Bio-gas to control rice storage pests. IRRI Newsletter, 11 (6), 25.

Tyler, P. S., Taylor, R. W. & Rees, D. B. (1983). Insect resis- tance to phosphine fumigation in food warehouses in Bangladesh. Int. Pest Control, 25 (1), 1 O- 13.