Non-chemical alternative in rice storage: the use of refrigeration for insect control and quality maintenance of paddy rice

Trials were conducted to evaluate the potential effects of refrigeration in controlling insect infestations of Sitophilus zeamais and S. oryzae on stored rice. In the rice storage and processing industry use of aeration systems during winter and refrigeration units under summer conditions can provide a good solution to reduce paddy temperature for control of insects and maintenance of paddy quality; though it is restricted by costs of machinery and electric power. Trials were conducted in a rice mill in Portugal close to the Mondego Valley. A granary containing 140 t of paddy (variety Ripallo) was cooled using refrigerated aeration because during the trials ambient temperatures were too high for successful insect control by ambient air aeration. Sitophilus zeamais and S. oryzae adults reared on brown rice at 28°C and 68±3% r.h. were used as bioassays. Paddy stored in the granary was cooled to below 18ºC from 27 June 2008 to 19 September 2008. The mean ambient temperature during the total period of the trial varied from 12ºC to 27ºC. The moisture content of the paddy in the granary ranged from 12.1% to 13.9% during the same period of time. The total F1 of adult emergence population of S. zeamais and S. oryzae was counted after the experiments. The F1 adult from parent adults of S. zeamais was reduced up to 77%; the F1 adult from eggs of S. zeamais and S. oryzae were also reduced up to 71% and 45%, respectively, when compared with corresponding untreated controls. Refrigeration of the paddy allowed storage for almost three months at about 18ºC and caused delay in rice weevils development. As a consequence, this negated the necessity for fumigation. Although the energy consumed during refrigeration doubled the cost when compared with cooling using an ambient-air, aeration system during the cold season, refrigeration provided an environmentally sound and user-friendly treatment during warm months of the year. Keywords: Refrigeration, Sitophilus zeamais, Sitophilus oryzae, Paddy, Rice mill, Storag