Post-harvest insect pest directory
American black flour beetle
Scientific name: Tribolium audax (Halstead)
- Order
- Coleoptera
- Classification
- Secondary
- Incubation at 20 C
- 7-10 days
- Incubation at 30 C
- 3-5 days
Description
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.
Detection
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.
Damages
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.
Environment
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.
Infested products
Cereals, flour, animal feed, seeds, and cereal products.
Life cycle
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.
Geographical distribution
World.
Similar species
European black flour beetle (Tribolium madens)
Red flour beetle (Tribolium castaneum)
Confused flour beetle (Tribolium confusum)