CONTROL OF STORED GRAIN INSECTS BY USING NITROGEN IN LARGE CONCRETE SILOS IN CYPRUS

Nitrogen (N2) was applied in three concrete silos each containing 2,400 tonnes of grain for controlling stored grain insects. Structural sealing was carried out and air tight valves were installed to improve the air tightness of the bins. Pressure decay tests (250-125 Pa) carried out in full bins showed decay time from 120 s up to 290 s. Using a PSA N2 generator the oxygen (O2) concentration was reduced in 44-56 h below 0.9% and after that it was continuously maintained between 0.2-0.9% up to 23.8 days. Treatment of 18.7 and 23.8 days on grain temperature of 26°C and 22°C, respectively, was effective for the control of the adults of important stored grain insects Oryzaephilus surinamensis (L.), Tribolium confusum J. du Val and Rhyzopertha dominica (F.) placed above and inside grain mass. In separate bioassays, which were placed in different zones right above the grain mass complete (100%) mortality of T. confusum (all life stages), O. surinamensis (larvae and adults), Sitophilus granarius (L.)(adults) and R. dominica (adults) was achieved in 18.7 and 23.8 days treatment as well. When applied to large quantities of grain, the N2 modified atmosphere (MA) technology by using a N2 generator proved to be cost competitive with the analyzed other treatment methods. Under trial conditions the cost of annual treatment of 40,000 tonnes using the PSA of EcO2 system is about 1.6 €/tonnes in comparison to 0.5-0.8 €/tonnes by using Siroflo/ECO2FUME, 0.4-0.8 €/tonnes by using contact insecticides and 0.40 €/tonnes for aeration. By increasing the annually treated quantity to 130,000 tonnes the treatment cost with N2 MA EcO2 system is estimated 0.80 €/tonnes. The N2 MA provided a full control of studied stored grain insects, free-residues products, no environment chemical contamination, low occupational hazard, no-dependence on insect resistance, no need for registration and full control and automation of the treatment operation. On the basis of these trials the N2 MA technology is a successful alternative to phosphine Siroflo/ECO2FUME and contact insecticides for the control of stored grain insects in large concrete silos.