Broad bean weevil (faba bean weevil)

Broad bean weevil (Bruchus rufimanus) is a small, stout bruchine, 3.5–5 mm long, with a short‑oval habitus. The elytra almost entirely cover the abdomen. A key diagnostic trait is the rufous femur on the forelegs. Do not confuse it with the pea weevil (Bruchus pisorum): that species has a black fore femur, a distinct white macula on the prothorax, and an oblique white stripe on the elytra. These characters allow quick, reliable separation during faba bean inspections.

In storage, larvae remain endophytic within the seed, boring galleries through the cotyledons and sometimes the embryo. This internal feeding hollows kernels and removes dry matter, reducing test weight and thousand-seed weight. Adults create characteristic circular emergence holes in the testa, leaving perforated, fragile seeds. Lots become contaminated with frass and insect fragments, increasing fines and breakage and downgrading overall quality. Such damage renders grain unsuitable for human or animal consumption and markedly decreases commercial value. Injury to the embryo compromises viability, causing reduced germination and unreliable performance of seed stocks intended for planting.

Key signs of Bruchus rufimanus (broad bean weevil) infestation in stored faba bean grain: - Colonized seeds perforated by circular emergence holes in the testa, giving a “shot-holed” appearance. - Pre-emergence “windows”: thin, translucent spots on the seed coat over the pupal cell. - Internal larval galleries in the cotyledons, with compacted frass and a defined pupal chamber visible on cross-section. - Powdery frass/seed dust accumulating in bags and bins. - Degraded visual quality: pitted, chipped, and perforated seed coats; higher breakage during handling. - Reduced germinative capacity: damaged embryos, missing radicles, and abnormal seedlings on germination tests. - Occasionally, presence of live bruchid adults in the lot, indicating ongoing emergence.

Broad bean weevil (Bruchus rufimanus) is univoltine. Adults become active around 20°C, with >25°C favoring flight, mating and oviposition. Females lay eggs on faba bean pods; upon eclosion, the neonate larva immediately penetrates the pod and enters a seed. The larva is endophagous and completes several instars within a single bean (multiple larvae may coexist under high pressure). Pupation occurs inside the seed; the teneral adult (imago) emerges by cutting a perfectly round exit hole, often noticed at harvest or during storage. Adults then disperse to overwintering sites; fields close to silos are often more exposed. Critically, unlike cereal weevils, B. rufimanus does not reproduce in stored grain; no new infestation starts in storage.

Bruchus rufimanus favors stored-grain settings—silos and warehouses—where dense faba bean lots and stable microclimates ensure easy food access, promoting adult aggregation and larval endophagy inside seeds.

Bruchus pisorum: pea weevil. Bruchus signaticornis: no widely used English common name; a bruchid/seed beetle. Bruchus affinis: lesser pea weevil. Bruchus brachialis: vetch bruchid. Bruchus atomarius: no widely used English common name; a bruchid/seed beetle.