Flat grain beetle (Cryptolestes spp.)

Type of pest: Secondary pest.

These insects are often grouped together as the ‘flat grain beetles’. Technically they are the rusty grain beetle, Cryptolestes ferrugineus, the flat grain beetle, Cryptolestes pusillus, and the flour mill beetle, Cryptolestes turcicus.

Distribution: C. ferrugineus and C. pusillus worldwide, others more restricted. Some species are cold-tolerant.

Identification: All three species are red-brown in color and about 1.5 – 2 mm long. They are flat and quite shiny and have rather long, slender hair-like antennae, up to the length of the body. A ridge runs from above each eye down each side of thorax. Adult beetles are strong fliers. Larvae: campodeiform. The larvae are white and slightly flattened, growing to about 3mm long.

Similar species: Ahasversus, Cathartus. Species difficult to distinguish except by examination of genitalia.

Life cycle: For the C. ferrugineus the females will begin laying eggs within four days after emergence and oviposition continuously for more than 34 weeks. Eggs are deposited singly in crevices or furrows in kernels of grain, in spaces between kernels, or in debris. Newly-emerged adults remain within the cocoon for a few days before chewing out. Larvae are mobile and external feeders. Adults are long-lived, walk with a characteristic sway, and feed on commodities and fly.

Development from egg to adult varies between species, with the rusty and flat grain beetles taking 22 – 24 days at 32 – 35°C and 75% r.h. while the flour mill beetle requires about 30 – 35 days.

Commodities infested: They can be found feeding on grain and cereal products, other dried material of plant origin, packaged and processed goods. They have been recorded in wheat, corn, rice, barley, flour, oilseeds, cassava root, dried fruits and chilies. Larvae feed preferentially on the germ of the whole kernels, but they also feed on the endosperm and sometimes hollow out the entire kernel. Growth of mold in the endosperm renders it more suitable as larval food. Cryptolestes species are apparently unable to feed on sound grain, but they can feed on kernels with very slight imperfections or injuries.

Treatment: Controlled Atmosphere for infestation in product
Treatment: Heat Treatment for infestation in buildings