Small matte darkling beetle

Alphitobius diaperinus (Panzer), the small matte darkling beetle, has adults dark reddish-brown to black, 5.5–7.0 mm long, with a dull, matte integument. The compound eyes are shallowly emarginate; at their narrowest the bridge spans 2–3 ommatidial facets—diagnostic for this species and distinguishing it from A. laevigatus, where the constriction narrows to a single facet. Larvae are brown-yellow, cylindrical, and reach about 15 mm at maturity.

This tenebrionid causes non‑diagnostic damage in stored grain. Both adults and larvae attack commodities. A secondary pest, it preferentially exploits cracked kernels, fines, and milled fractions. Adults abrade the pericarp and endosperm; larvae rasp softer tissues, leaving irregular surface grazing and shallow pits rather than neat perforations. Activity generates fines and dust, reduces test weight, and contaminates lots with frass, exuviae, and cadavers. Metabolic heat and added moisture create warm, humid pockets that foster mold growth and musty off‑odors, and can facilitate mite proliferation. Seed lots may suffer reduced germination where the embryo is injured. Heavy infestations lead to clumping/caking and downgrading due to visible contamination and quality loss.

Signs of infestation indicating the presence of the small matte darkling beetle, Alphitobius diaperinus (Panzer), in stored grain: - Unpleasant, nauseating off-odors from the lot—often an early warning sign. - Live stages present: larvae and adults (imago) observed in intergranular spaces, along seams, and within fines. - Feeding injury to kernels: surface abrasion, nibbling of germ/endosperm, pinholes, and an increase in fines/powder. - Frass and exuviae: dark, granular fecal pellets and cast larval skins (exuviae), with scattered shed cuticle. - Grain heating: localized “hot spots” caused by insect metabolic activity, sometimes preceding visible damage.

Alphitobius diaperinus (Panzer), the small dull darkling beetle, is a holometabolous stored‑product pest. After mating, females oviposit egg masses directly within grain and residues. Embryos hatch into active, scavenging larvae that move freely among commodities, penetrating fines and sheltering in crevices. Larvae progress through successive instars before pupation within the substrate or nearby refugia. The teneral adult emerges, sclerotizes, and soon becomes reproductively active. Adults are long‑lived (≈400 days) and capable of flight, enabling rapid colonization and reinfestation of storage structures. Overlapping cohorts sustain infestations wherever food, warmth, and moisture persist.

A hygrophilous, saprophagous pest, it favors warm, humid, mold-rich niches: damp cereals, milled grain products, and moist feed. In poultry houses it exploits litter and droppings. Thrives in heated shelters; not on sound, dry grain; poor overwinter survival unheated.

Mushroom darkling beetle (Alphitobius laevigatus)