Drugstore beetle (biscuit beetle)

Drugstore beetle (Stegobium paniceum). Adults are small, oval, reddish-brown beetles, 2.5–3.0 mm long. Antennae terminate in a distinct 3-segmented club. The elytra are longitudinally striate and clothed with fine pubescence; the body bears minute setae, giving a subtly matte aspect. Adults are short-lived, feed little or not at all, and are capable fliers. Larvae are white, soft-bodied, and covered with numerous hairs (setae).

Prefers synanthropic stored‑product settings: homes, shops, bakeries, libraries, ships, mills, warehouses. Feeds on dried goods, favoring starch‑rich plant substrates; minor in grain stores, it may enter hives to consume pollen.

Signs indicating infestation by the Drugstore beetle, Stegobium paniceum (Linnaeus), in stored grain:

- Silken cocoons (pupal cells) spun by larvae, often adhered to kernels or structure and packed with frass.

- Powdery frass (fine fecal pellets) and siftings accumulating in seams, on ledges, and beneath sacks.

- Dead adults among the grain; small, reddish-brown beetles ~2–3.5 mm.

- Round, cleanly bored perforations in kernels and in packaging (paper, cardboard, plastic, foil), made by late-instar larvae at pupation and by emerging adults.

- Larval galleries within kernels, leaving weakened, hollowed grain and fine powder.

These indicators warrant prompt inspection, sanitation, and containment to prevent spread.

Drugstore beetle (Stegobium paniceum). Adults are active on surfaces and strong fliers. After mating, females oviposit singly into cracks and fissures of stored grain and other commodities. Neonate larvae penetrate the substrate; they are endophagous, feeding within the food mass. Initially mobile, larvae become increasingly sedentary as they approach the final instar, reaching 3–4 mm at maturity. The mature larva constructs a compact, frass-lined cell within the commodity and pupates. Teneral adults eclose, bore out of the product, and disperse by flight to colonize new lots, completing the cycle. Development rate and generations per year depend on temperature and humidity.

This stored‑product beetle damages grain mainly as larvae. Larval instars tunnel and excavate irregular galleries into kernels and fines while feeding and preparing for pupation, leaving pitted or hollowed grains and accumulations of powdery frass with cast skins. Resulting losses include weight reduction, lower test weight, and downgrading of lots; seed viability and milling quality can be impaired. On emergence, adults perforate packaging (paper, cardboard, thin plastics), creating exit holes that enable spread and cross‑infestation. Infested grain often shows clumping from frass, off‑odors, and heightened susceptibility to secondary molds and mites.

Tobacco beetle (Lasioderma serricorne)