EFFICACY OF INERT MATERIALS AGAINST RICE WEEVIL , SITOPHILUS ORYZAE ( COLEOPTERA ; CURCULIONIDAE ) IN MILLED RICE GRAINS

Gayatree Sahoo and Braja Kishore Sahoo. Department of Entomology, Orissa University of Agriculture and Technology, Bhubaneswar, Odisha, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Grain storage is a serious problem confronted by every farmer and householder in developing countries like India by the insect pest attack where a considerable quantity of food grain is lost every year. Stored products of agricultural and animal origin are attacked by more than 600 species of beetles, 70 species of moths and 355 species of mites causing quantitative and qualitative loss. Among the several insects attacking stored grains, Sitophilus oryzae L. (Coleoptera: Curculionidae) is the most destructive insect pest of the stored raw cereal grains in the world (Champ and Dyte, 1976). Itcauses substantial losses to stored grain amounting 18.30 per cent (Adams, 1976). The use of inert dust to control stored grain pests is a technique with a long history and has been reviewed by many authors (Aldryhim, 1990). The inert dusts already exist in nature but are usually over looked by the households. Besides being very safe and presenting low toxicity in mammals, the inert dust does not affect the grain quality (Ebeling, 1971; Aldryhim, 1990). The main advantages of using inert materials are easy production by farmers, less expensive, biodegradable, broad spectrum, safe to apply, unique in action and are non-hazardous and non-toxic to human. In India few scientific research works have been done to explore locally available inert material for the management of harmful insect pest in storage by the farmers. So the present study was undertaken to study the bio efficacy of certain inert materials against rice weevil in milled rice grains.

Materials and methods:-
The OUAT released "Jyotirmayee" variety of rice was selected for the experiment. The treated grains were prepared by mixing the specified dose of inert materials to 1kg of milled rice grains and it was kept as such in a flask for 24 hours. Then the treated grains were ready for the experiment. The experiment was carried out at room temperature 29.23 + 1.67 0 C and RH 59.1 + 2.32 %.
The screening of the inert materials was carried out during December-2015 to April-2016 with treated milled rice grains in a completely randomized design (CRD) with three replications along with one untreated check. The moisture content of the grains were standardised at 11.5 percent level. Fifty grams of milled rice were taken in 150gm capacity plastic jars and then five pairs of newly emerged adults of Sitophilus oryzae L. were released. The mouths of the jars were closed with muslin cloth and tightened with the help of rubber band.
Observations were taken on population build-up of the Sitophilus oryzae L., grain damage (%), grain weight loss (%), inhibition rate, reduction in grain damage and grain weight loss (%) at 30 days interval up to 150 days after release and the increase in moisture content was recorded at the end of the screening process by using Digital moisture meter.  Table 1. At 30 DAT in different treatments the adult S. oryzae population increased and were between 10.00 to 25.33 per 50 gm of milled rice samples and in untreated check the initial population was increased from 10.00 to 33.67. In the treatment of diatomaceous earth @0.5% no increase in the population was observed. But the treatment with sand @0.5% the population reached at 25.33 no. per 50 gm sample.
At 60 DAT minimum a population of 11.33 was observed in diatomaceous earth @0.5% treatment followed by camphor, boric acid, sodium bicarbonate and salt all @0.5% with 15.00, 18.00, 24.00 and 26.33 nos. per 50 gm of sample respectively. A highest population was observed with sand @0.05% with a adult weevil population of 38.00 as compared to untreated check (77.33). The same trend was also observed at 90 and 120 DAT.
Similarly 150 DAT the lowest S. oryzae population build up of 17.33 was observed in the treatment with diatomaceous earth followed by camphor (29.67), boric acid (37.33), sodium bicarbonate (42.33) and salt (45.33) respectively over the untreated check of 257.67. a highest population was observed in the sand treatment with 102.33 no.s of adult weevil per 50 gm of milled rice grains.
The highest inhibition rate (IR) of the adult S. oryzae population was recorded with the diatomaceous earth treatment of 93.27% followed by camphor (88.49%), boric acid (85.51%), sodium bicarbonate (83.57%) and salt (82.41%) over the untreated check. The lowest IR was recorded in ash and sand treatment with 77.62 and 60.29% respectively.

Effect on grain damage (%) and Grain weight loss (%):-
At 30 DAT lowest grain damage and grain weight loss of only 1.12 and 1.31% was observed in the diatomaceous earth @0.5% treatment respectively. It was followed by camphor (1.51% grain damage and 1.83% grain weight loss) and boric acid (3.11% grain damage and 1.34% grain weight loss) as compared to the untreated check (18.19% grain damage and 15.19% grain weight loss). Similar trend was also observed at 60, 90 and 120 DAT. At 150 DAT in the diatomaceous earth @0.5% treatment the lowest grain damage and grain weight loss of 5.12 and 4.92% was observed respectively. The next best treatment was camphor with grain damage of 7.72% and grain weight loss of 5.33% as compared to the untreated check of 58.49 and 40.12% grain damage and grain weight loss respectively.
( Table 1) 2575 The reduction over grain damage and grain weight loss over the untreated check was observed in the diatomaceous earth treatment with 91.25 and 87.74% respectively which was followed by camphor (80.60 and 86.71%), boric acid (85.31 and 81.68%), sodium bicarbonate (82.00 and 78.79%) and salt (78.90 and 67.90%) respectively. The lowest IR was recorded in sand treatment with 70.58 and 57.85% grain damage and grain weight loss respectively.
At the end of screening process i.e. at 150 DAT an increase in the grain moisture content was recorded in every treatments and it has been recorded and presented in Table 2. The final grain moisture content was recorded between 13.1 to 14.1% and 16.5% in the untreated check. The lowest moisture content of 13.1% was reported in the diatomaceous earth treatment followed by camphor (12.9%), boric acid (13.1%) and sodium bicarbonate (13.4%) whereas the highest in sand with the grain moisture content of 14.1%.    Ahmed (2015) reported the advantage of using boric acid is that, it destroys the cellular lining of the foregut of insects which strengthens and proves the present finding that boric acid is the next best treatment after diatomaceous earth and camphor. Mulungu et al., (2010) reported that when sodium bicarbonate used @ 2% (w/w), the grain weight loss by S. zeamais was only 50 g/ 200g sample maize grain over the control which is deviated from our reports.
According to Karthikeyan et al. (2006) ash treatment during storage was found effective for controlling the storage losses up to 80% which contradicts the present finding of reducing the grain weight loss up to 57.85% only.
At the end of screening process i.e. at 150 DAT an increase in the grain moisture content was recorded between 13.1 to 14.1% and 16.5% in the untreated check. The lowest moisture content of 13.1% was reported in the diatomaceous earth treatment whereas the highest in sand with the grain moisture content of 14.1%. As per Delouche (1973) the seed moisture content is a function of ambient RH and the infestation, growth and reproduction of storage insects which competently supports the present findings.