Tribolium audax (Halstead), the American black flour beetle, is a small tenebrionid. Adults (imagines) measure 2.8–4.5 mm in body length, with an elongate habitus and relatively round, convex compound eyes—contrasting with the more oval eyes of the European black flour beetle. Larvae are dark brown, cylindrical, and elongate.
Damage in stored grain is not distinctive. As a secondary colonizer, adults and larvae exploit broken kernels, fines, and processed fractions, abrading pericarps and endosperm and converting material to floury dust. Infestation leads to abundant frass, exuviae, and carcasses, contaminating lots and increasing dockage. Feeding and respiration create warm, humid pockets that promote caking and mold. Quinone defensive secretions impart taint, off-odors, and brownish discoloration to grain and meal. Heavy populations lower test weight, reduce germ viability, and downgrade market grade, with quality losses in milling and baking performance. Visual signs mirror those of other flour beetles and similar secondary stored-product pests.
Signs of infestation indicating the presence of the American black flour beetle, Tribolium audax (Halstead), in stored grain include: - Offensive, quinone-like odor from benzoquinone defensive secretions. - Presence of adults and larvae on the grain surface, within fines, and along seams; accumulations of dead beetles may occur. - Exuviae (cast skins), fragmented elytra, and beetle body parts mixed with the commodity. - Kernel damage: perforations, surface rasping, partially consumed or hollowed kernels. - Floury frass and fines producing dusting, clumping, and a mealy texture. - Localized temperature rise (“hot spots”) and caking due to insect activity and associated microflora.
Tribolium audax (American black flour beetle) is a holometabolous stored-product pest. Females disperse their eggs—up to 1,000—among food sources within stored commodities. After eclosion, campodeiform larvae feed within the bulk and pass through successive instars, then pupate in situ. Quiescent pupae transform into active adults. Adults live on average 2–3 months, continuing to feed and mate within the grain mass, producing overlapping generations under storage conditions. Infestation results in frass, off-odors, and caking that degrade grain quality.
The American black flour beetle (Tribolium audax) prefers empty granaries in Western Canada, occupying storage structures rather than the grain mass; it generally does not infest stored grain.
European black flour beetle (Tribolium madens) Red flour beetle (Tribolium castaneum) Confused flour beetle (Tribolium confusum)
Receive our studies and news directly by e-mail.
We just sent you an email with a confirmation link.
Check in your spam folder if you don't see it in your inbox.