Influence of Different Stored Grains on Adult Emergence Rates and Weight Loss by the Rice Weevil Sitophilus oryzae (Coleoptera: Curculionidae)

The internal-feeding insect, Sitophilus oryzae L. (Coleoptera: Curculionidae) is a ubiquitous and significant pest that burrows into grain that has been stored. The larvae of weevils feed mostly on the grain germ, eliminating a significant portion of the protein and vitamins, whereas adult weevils primarily feed on the endosperm, decreasing the amount of carbohydrates. In this study, S. oryzae infestation was monitored on five types of grains: rice, wheat, oat, maize, and barely. The grains were kept at 32 ± 2 °C, 65 ± 5% RH, and a 14:10 (L:D) h photoperiod. The results revealed that both wheat and maize were the most susceptible grains to the insect. Wheat grains were generally more preferred in both non-choice and free-choice tests, whereas oats were the least preferred in this respect. The different grains had a significant effect on adult emergence and weight loss by this insect. In non-choice test, the highest average number of the emerged adults of S. oryzae after 30 and 60 days was recorded on wheat grains (11.8±0.96 and 16.8±0.86 indiv.) followed by maize grains (8.8±1.15 and 15.2±1.56 indiv.), In free choice test, the highest average number of the emerged adults was recorded on wheat grains followed by maize grains and rice grains after 48 and 72 h from infestation.