Development of Granary Weevils and Storage Fungi in Columns of Wheat—II1

Abstract

Seed-grade wheat with a moisture content of 13% to 14% was stored in Transite cylinders 8 inches in diameter and 40 inches long, each of which held 23 kg. of grain. Two hundred adults of Sitophilus granarius (L.) were added to the grain in each of two cylinders and allowed to wander freely. Two hundred adult weevils were added to 2.4 kg. of grain in each of two brass cloth cages, one of which was placed at the bottom of each of another pair of cylinders, which were then filled with grain. Another pair of cylinders filled with grain served as controls. The cylinders were kept at 25° and 65% to 70% relative humidity. Samples of wheat were withdrawn through side ports, with minimum disturbance to the bulk, after 2,4, and 6 months, and tested for moisture content, fungus population, germination, insect damage, and number of insects. Where insects were not confined, the moisture content increased to 20% in the upper portion of the grain; throughout the bulk, moisture content increased several per cent and storage fungi increased greatly. The greatest increase in temperature was approximately 6° (10.8° F). Where insects were confined at the bottom of the column of grain, moisture content increased as much as 8% in the grain several inches above the infested portion and approximately 0.5% in the grain 1 to 2 feet above the infested portion. The grain in the controls remained essentially unchanged. Fumigation with a commercial formulation killed all the insects hut had no effect on the population of storage fungi which continued to increase after fumigation.