The use of modified atmospheres to control Sitophilus zeamais and Sitophilus oryzae on stored rice in Portugal

This study reports the efficacy of using CO2 against Sitophilus zeamais and Sitophilus oryzae as an alternative treatment to fumigation for rice stored in a rice mill in Portugal. The trials were conducted in a silo containing 40 tonnes of polished rice and in four hermetic big bags of 1 tonne capacity; two with paddy and two with polished rice. The composition of the atmosphere ranged from 90 to 95% CO2 and 0.7–2.1% O2. Three trials were carried out at different temperatures and treatment times; stored rice in the silo at 29.6 ± 0.1 °C for 26 days (first trial), at 34.1 ± 0.2 °C for 10 days (second trial), and in big bags at 22 °C for 26 days (third trial).To evaluate the efficacy of each treatment, metal cages with 16 g of infested rice where placed at bottom, middle, top and surface of the polished rice in the silo. Four replications of each type of infested rice containing one-week-old S. zeamais adults, or eggs of S. zeamais or S. oryzae, were incubated in the laboratory, at the same temperature as in the silo, to serve as a control.In all modified atmosphere treatments adults of S. zeamais, and eggs of both S. oryzae and S. zeamais, showed mortality close to 100% and no F1 emergence was recorded in any treatment sample. This was the first time that a Portuguese rice mill used modified atmospheres.

► Trials were carried out using CO2 in stored rice: in a silo at 31 °–32.7 °C for 26–10 days, respectively, and big bags at 22 °C for 26 days. ► The treatments suppressed all stages of Sitophilus spp., the time of gas exposure depending on grain temperature. ► No difference on sensory qualities of cooked rice, between treated and non-treated polished rice. ► The results confirmed the use of CO2 is an efficient alternative method to Fumigation to control stored rice pests.