Lesser grain borer

Lesser grain borer, Rhyzopertha dominica (F.): the adult is a small, dark reddish-brown beetle, about 3 mm long, with antennae terminating in a diagnostic, loose three-antennomere club (clavate). The larva is white, with a dark-brown head capsule, strongly curved (C-shaped), and becomes immobile at maturity.

A primary internal feeder of stored cereals. Both adults and larvae penetrate intact kernels, excavating galleries through the endosperm (albumen) and into the germ. Feeding progressively hollows the kernel, often leaving little more than the bran/pericarp as a fragile shell. Continuous tunneling generates fine, floury frass and boring dust, with round perforations and exit holes visible on heavily attacked grain. Damage results in lightweight, brittle, riddled kernels, shrinkage, and significant loss of marketable weight. Lots become contaminated with frass and bran shells, with elevated breakage during handling and a clear downgrade in grain quality.

Key signs of Rhyzopertha dominica (F.), the lesser grain borer, in stored grain: - Heavy accumulations of flour‑like boring dust (frass) and fines around spouts, ledges, and in sievings. - Irregular internal galleries and hollowed kernels; ragged “shot‑holes” (adult emergence holes) on grain and packaged products. - A distinct sweet, malt‑ or honey‑like odor emanating from the lot. - Visible adults: small, cylindrical, dark‑brown beetles (≈2–3 mm) appearing in probe samples and auger discharge, often concentrated in warm hotspots. - Increased cracked grain and lightweight, insect‑damaged kernels; localized heating and caking where activity is intense.

Rhyzopertha dominica (F.), the lesser grain borer, is a primary pest of stored grain with a holometabolous life cycle (egg–larva–pupa–adult). Adults are long‑lived, highly mobile, and strong fliers. Females oviposit either singly or in masses of up to 30 eggs. After eclosion, neonate larvae bore into sound kernels and feed endophagously; because development occurs concealed within the grain, larvae are rarely detected in sieve-based samples. Larvae complete development and pupate in situ inside the same kernel, producing adults that sustain ongoing infestations.

Lesser grain borer (Rhyzopertha dominica) favors indoor storage buildings with stored commodities, typical synanthropic stored-product habitats, and only occasionally infests shipping containers.

Lesser grain borer (Rhyzopertha dominica)