Mezium affine Boieldieu, 1856

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POLYPHAGA Emery, 1886

BOSTRICHOIDEA Latreille, 1802

PTINIDAE Latreille, 1802

PTININAE Latreille, 1802

MEZIINI Bellés, 1985

Mezium Curtis, 1828

Thought to be native to Africa, this species is now generally considered to be cosmopolitan in distribution although it is only infrequently established e.g. in Australia, and its occurrence in temperate regions is sporadic and infrequent; it is common in warmer regions of southern Europe but only occasionally recorded from central and northern countries, including the UK where it has been recorded since the 19th century, it was first recorded in the United States in 1904 and is now established and widespread in both the United States and Canada. It is unlikely to survive outside in cooler temperate regions but in southern Europe they occur among decaying plant and animal materials and have been recorded from bird nests, rodent burrows and bat roosts, it is otherwise usually recorded as a pest of stored products and in some countries it is widely available as exotic pet food. Adults have been recorded throughout the year both in the wild and under artificial conditions and they are thought to be continuously brooded, they are extremely drought-tolerant and can survive extended periods without water, similarly the larvae can develop on cardboard or biscuits in a dry atmosphere and grow as fast as those reared on fresh vegetables, they are therefore able to infest a very wide variety of stored products. Cultures have been maintained at all temperatures from 20-33°C and relative humidities from 30-70%, the fastest development time from egg to adults was 62 days at 29-33°C in a range of humidities, and because the species is moderately fecund large populations occasionally occur among foodstuffs; a tenfold increase in adult numbers has been recorded over a three month period. Cultures have been raised on grains and spices, seeds, dried meat, fungi and fruit, fish meal and biscuits, and larvae have been found developing among hair, wool, feathers, dry insect specimens, book bindings and faeces and the species is an occasional pest of many types of museum specimens, especially in warmer climates.

Adults are small, 2.5-3.5mm, and quite unlike any other UK species; the forebody and appendages are densely covered with pale scales which range from creamy to brilliant yellow, and the elytra, which is shiny and glabrous but for a few long and erect setae along the basal quarter or half and towards the apex, is usually reddish-brown although this is very variable and dark green or blue specimens occur; some cultures include deep blackish-violet specimens which have earned the common name of egg-plant beetles. Head ventrally inclined and not visible from above, eyes small and weakly convex between wide and flat frons, antennae inserted close together, 11-segmented and filiform; the scape deeply emarginate apically and the pedicel strongly widened from the base to a parallel-sided apical half. Pronotum quadrate, steeply sided and raised and impressed medially and with a deep transverse impression before the base. Scutellum widely transverse but usually indistinct. Elytra elongate and oval, without shoulders and widest behind the middle, smoothly convex and lacking striae or obvious punctures; usually with scattered setae along the base and sometimes towards the apex but in extreme examples these may more-or-less cover the elytra, suture fused (the species is flightless). Legs long and slender, apical half of femora strongly widened and femora and tibiae laterally flattened. Tarsi 5-segmented, without obviously lobed segments, claws tiny, smooth and without a basal tooth.

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