Rusty grain beetle (flat grain beetle)

Rusty grain beetle (flat grain beetle), Cryptolestes ferrugineus (Stephens). Adult: a minute, glossy rufous to mahogany-brown beetle, 1.5–2.0 mm long, with a distinctly dorsoventrally flattened body—about the thickness of two stacked 10‑cent coins. Larva: slender and slightly flattened, 1–4 mm long (often 3–4 mm), white to yellowish-white with a brown head capsule; the terminal abdominal segment is slightly darker and prolonged into a pair of amber urogomphi.

Larvae and adults injure stored grain by consuming the embryo (germ) and endosperm, compromising kernel integrity and destroying seed viability—especially in malting barley and other seed lots. Rapid population growth generates metabolic heat, creating localized “hot spots” that warm the bulk and accelerate spoilage. Severe infestations thus cause heating and overall grain deterioration. Populations also disseminate fungal spores, facilitating mold development within storage. Beyond whole grain, they attack cereal products, dried fruits, peanuts, oilseed cakes, and herbs, enabling cross-infestation among stored commodities.

Signs of infestation by the rusty grain beetle, Cryptolestes ferrugineus (Stephens), in stored grain: - Grain heating: localized “hot spots” and temperature rise (often >2–3°C above ambient) from insect respiration. - Moisture migration: condensation on walls/roof, surface crusting, caking/bridging over warm zones. - Odors and spoilage: sweet–musty or sour smell, followed by mold bloom in heated pockets. - Fine residues: floury frass and increased fines around the grain surface, spouts, and under crusts. - Visual detection: very small, flat, fast‑running reddish‑brown adults (~1.5–2 mm) in probes, sieves, or sticky/pitfall traps; slender, cream larvae with dark head concentrated in warm, dusty areas. - Grain condition: clumping, discoloration, reduced test weight, and damaged or germ-end‑scored kernels (often secondary to prior injury or fungal growth). - Elevated CO2 readings from increased respiration. Note: These signs can resemble those caused by other stored‑product beetles; confirmation requires capture and identification of adults/larvae.

Rusty grain beetle (Cryptolestes ferrugineus). Females oviposit 200–500 eggs loosely on or among grain and debris. Neonate larvae disperse by crawling and preferentially consume the germ, developing in and around cracked kernels. After several instars, pupation occurs within a debris-lined cocoon; adults eclose in 5–12 weeks, depending on temperature. This species shows very rapid population increase in stores, yet reproduction slows markedly below 23°C, and adults do not fly below 21°C. Development is inhibited when grain moisture is <12% and relative humidity <40%. Adults cannot climb smooth glass. Among stored-product beetles, it is notably cold tolerant.

Prefers bulk stored grain masses in on-farm bins and silos, and in conveyances such as ships and railcars; a frequent granivorous pest in Canadian farm-stored grain, but uncommon in mills and warehouses.

Cucujide plat (Cryptolestes pusillus): flat grain beetle. Cucujide longicorne (Cryptolestes turcicus): flour mill beetle.