Demography of Rusty Grain Beetle in Stored Bulk Wheat: Part I, Population Dynamics at Different Temperatures and Grain Bulk Sizes.

Population dynamics of rusty grain beetle, Cryptolestes ferrugineus (Stephens; Coleoptera: Cucujidae), was studied using different sizes of grain bulks (patches) at various temperatures. The temperatures were 21, 25, 30, 35°C, T-decrease (30°C in the first 4 wk and then decreased 1°C /wk), and T-increase (21°C in the first 2 wk and then increased 1°C /wk). Number of adults and offspring and infested wheat kernels were counted every 4 wk up to 24 wk (31 wk for the T-decrease). The grain bulk patches used were: small (50 ml inner volume, 0.03 kg wheat), medium (2.6 liters inner volume, 2 kg wheat), and large (18 liters inner volume, 14 kg wheat). All of the correlation coefficients between the insect numbers and kernel infestation percentage were ≥0.63. Two types of the population dynamic curves were observed: insect number or density continually increased with time during the entire experiment, or there was a rise then a fall in insect number or density over time, giving a peak number or density. The peak insect density was approximately 400 to 500 adults/kg of wheat for all patches at 30°C or lower. At 35°C, the peak densities of live adults were 3,956 ± 630, 2,094 ± 34, and 1,003 ± 70 adults/kg of wheat in small, medium, and large patches, respectively. Patch size influenced insect population dynamics at 35°C. Insect number inside large patch was more dependent on the previous insect number than that inside small patches.