Larger grain borer

Prostephanus truncatus adults are black to dark brown, with a compact, cylindrical habitus and a length of about 3–4 mm—slightly larger than the lesser grain borer (Rhyzopertha dominica). The head is hypognathous, directed downward. The elytra terminate in an abruptly declivous apical slope bearing two strong lateral carinae that create sharp angular margins. Overall appearance is tubular and robust. Larvae are virtually apodous and become progressively less mobile as development proceeds.

Prostephanus truncatus, a stored‑product pest, is thermotolerant and xerophilic, thriving in dry grain. It colonizes maize‑ear storage (cribs, granaries) and can infest standing crops pre‑harvest, then proliferate in stored kernels.

Clear signs of Larger grain borer infestation, Prostephanus truncatus (Horn), in stored grain include:

- Numerous feeding galleries tunneled through the commodity.

- Kernels perforated with conspicuous, round entrance and adult emergence holes.

- Copious accumulations of fine boring dust and flour‑like frass within the grain mass and beneath storage surfaces.

These characteristic symptoms point strongly to P. truncatus activity.

Prostephanus truncatus (Horn), the larger grain borer, reproduces by ovipositing eggs singly or in small clusters on or near stored commodities. Upon eclosion, neonate larvae bore into kernels or feed on pre-damaged grain, frass, and adult feces. Several larvae may develop within a single kernel, excavating galleries as they feed. Larval development is followed by pupation (typically within the grain); emergent teneral adults harden, mate, and reinfest, producing overlapping generations and driving rapid population buildup in storage environments.

A highly destructive primary borer of stored grain. Adults excavate irregular galleries and ragged perforations through grain masses and cobs; larvae extend those tunnels within kernels. Feeding leaves copious flour-like frass and powdery fecal pellets, accumulating in seams, under bags, and in handling lines. Kernels are hollowed and reduced to meal, with conspicuous exit holes, causing severe weight loss, shrink, and reduced test weight. Extensive tunneling increases fines, porosity, and moisture migration, creating hot spots that favor mold development and mycotoxin contamination. Damage cascades into broken kernels, caking, off-odors, and significant qualitative downgrading, while predisposing lots to secondary pests (beetles and mites). In heavy infestations, entire lots can collapse into powdery debris, with penetration of packaging and cross-contamination of adjacent stocks.

Larger grain borer (Prostephanus truncatus)