Infestation, Population Density and Sterilization Effects on Rice Weevils (Sitophilus oryzae L.) in Stored Milled Rice Grains in Sierra Leone

Sitophilus oryzae (L.) is one of the most important insect pests infesting stored food grains. The level of infestation, population density, the relationship between damage level and weevil population in stored rice grain samples were investigated. The effect of hot air sterilization on weevil population density was also examined. Samples (including; 29 imported, 16 parboiled and 62 raw milled rice) were randomly collected from markets across Sierra Leone and subjected to storage treatments under laboratory conditions at room temperature (with and without prior sterilization). The results show a significantly higher number of rice weevils in raw milled rice (156.0) with correspondingly higher level of grain damage (1.28); than the imported (3.2 and 0.03), and parboiled (21.7 and 0.11) rice grains, respectively. This suggests that locally produced raw milled rice may be more prone to rice weevil infestation, than either parboiled or imported rice grains. Results of pre-storage sterilization treatment suggest that hot air sterilization eliminates weevils in stored rice, where as the unsterilized rice grains remained prone to rice weevil infestation. These results lead to the conclusion that the nature of rice grain products and pre-storage treatment influence the degree of rice weevil infestation during storage and that heat sterilization could be a useful option in the management rice weevil in stored rice grains.