Sawtoothed grain beetle

Adults are slender, dark brown beetles with a narrow, elongate, slightly flattened body, 2.5–4.0 mm long (typically about 3 mm). The pronotum (prothorax) has distinctly serrate lateral margins, producing the characteristic “saw-toothed” outline. Adults are morphologically very similar to the oilseed grain beetle but are distinguished by broader temples (wider temporal region behind the eyes). Larvae are pale white to yellowish, flattened, with a brown head capsule, reaching up to about 5 mm.

A cosmopolitan stored‑product pest and classic secondary colonizer, it exploits broken kernels, screenings, and grain dust. Adults and larvae abrade and consume fines; larvae preferentially attack the germ (embryo), gouging shallow galleries that destroy seed viability and depress test weight. Feeding and movement produce frass and exuviae that contaminate lots, elevate dockage, and impart musty, oily off‑odors. Aggregations in intergranular spaces raise localized temperature and moisture, creating hotspots that foster mold growth, caking, and accelerated spoilage, with increased mycotoxin risk. Infestations commonly extend to milled cereals, breakfast foods, dried fruit, and animal feeds across warehouses, silos, mills, and processing lines. Because sound, intact kernels are seldom penetrated, injury is diffuse and easily overlooked—yet heavy populations cause measurable quantitative loss, quality downgrades, and shipment rejection, especially in grain rich in brisures and fines.

Signs of infestation by the sawtoothed grain beetle, Oryzaephilus surinamensis (L.), in stored grain include: - Grain heating and “hot spots” from insect respiration; localized caking, condensation, and a musty odor. - Rapid population surges in warm, heated buildings; rising captures in probe or pitfall traps. - Visible life stages: fast, flattened brown adults with sawtoothed pronotal margins; cream larvae with brown head capsule; exuviae (cast skins). - Feeding damage: surface abrasion and fissures on kernels, eroded germ, and attack on broken kernels/fines. - Floury residues, frass, and increased grain dust accumulating in spouts, headspace, and beneath crusts. - Secondary effects: moisture pockets, mold blooms, and overall decline in grain quality.

Adults of Oryzaephilus surinamensis mate within stored commodities. Females practice scattered oviposition, depositing eggs loosely on the infested grain mass. After embryogenesis, larvae develop in the commodity and then pupate. Pupation is exarate: the pupa is free or enclosed in a light cocoon made from grain particles. Teneral adults emerge, sclerotize, and quickly restart reproduction. Total development (egg–adult) requires roughly 3–10 weeks, depending on climate. This species prefers warm temperatures, tolerates low relative humidity, is more cold-hardy than O. mercator, and can survive Canadian winters in unheated facilities.

The sawtoothed grain beetle is a synanthropic stored-product pest thriving in cereal granaries, warehouses, silos, and feed mills; a secondary colonizer of slightly degraded kernels, common in on-farm stored grain across Canada.

Merchant grain beetle (Oryzaephilus mercator) Foreign grain beetle (Ahasverus advena)