Management of drying and post-harvest chemical treatment in the control of Sitophilus spp. and Rhyzopertha dominica in stored rice

During storage, rice grains are susceptible to quantitative and qualitative losses caused by insects and fungi, compromising sanitary quality and increasing risks associated with fungal contamination and mycotoxin occurrence. This study evaluated how contrasting drying strategies—mixed-flow drying (55 °C) and low-temperature bin drying (19–25 °C)—influence grain moisture dynamics, insecticide persistence, pest control, and fungal incidence in stored rough rice. Preventive insecticide treatments consisting of pirimiphos-methyl alone or combined with deltamethrin were evaluated against Sitophilus spp. and Rhyzopertha dominica. The experiment was conducted in a commercial storage unit over 280 days under environmental conditions ranging from ∼19 to 27 °C, relative humidity of ∼70–90%, and precipitation between ∼5 and 85 mm. Grain moisture, insect mortality, and fungal incidence were monitored throughout storage. Mixed-flow drying promoted a faster reduction in grain moisture to approximately 12% (w.b.), whereas low-temperature bin drying maintained moisture levels close to 13% (w.b.) during storage. In addition, mixed-flow drying associated with pirimiphos-methyl + deltamethrin maintained Sitophilus spp. mortality close to 100% up to 160 days of storage, indicating greater insecticide persistence and pest control efficiency compared with low-temperature bin drying. In contrast, low-temperature bin drying maintained higher grain moisture, favoring an increase in Fusarium spp. incidence from 4.0 to 11.2% after 160 days, whereas Aspergillus spp. and Penicillium spp. predominated under mixed-flow drying, reaching maximum incidences of 13.8 and 6.6%, respectively. Although the combined insecticide treatment improved pest control during storage, efficacy against R. dominica remained limited, suggesting lower susceptibility and the need for complementary management strategies. These findings demonstrate that drying conditions directly influence grain microclimate and storage stability, highlighting the importance of integrating drying and chemical management to preserve sanitary quality and minimize storage losses in rough rice.