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 degrees C, T-decrease (30 degrees C in the first 4 wk and then decreased 1 degrees C /wk), and T-increase (21 degrees C in the first 2 wk and then increased 1 degrees 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 degrees C or lower. At 35 degrees 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 degrees C. Insect number inside large patch was more dependent on the previous insect number than that inside small patches.