Distribution of the Rusty Grain Beetle (Coleoptera: Cucujidae) in Columns of Wheat Stored Dry or with Localized High Moisture Content

Adults of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), moved downward after being placed at the top of 125- or 250-cm-high columns of wheat at 13 or 13.4% moisture content. From the first to the third day, most beetles were near the top of the column, but after 3 days most were found near the bottom. The number near the bottom increased over time. Beetle distribution in columns stabilized between the third and fifth day. Conversely, from 80 to 92% of the beetles aggregated at the top or middle zones of the column when wheat of 16 to 17% moisture content was placed only in these zones. Beetle distribution in the moist zones became stable within 3 days.