ribolium is a genus of flour beetles in the family Tenebrionidae. They are known by various common names including flour beetles, flour weevils, red weevils and bran bugs.
Adult Tribolium are beetles 3–6 mm in length and with colours ranging from reddish-brown to black. The clypeus is enlarged and has genae forming shelf-like projections extending around the sides, partly dividing the eyes. The antennae are 11-segmented and either expand towards the ends or have terminal clubs. The prothorax is nearly square in shape and rounded on the sides. The elytra are striated. They possess well-developed wings, but at least one species (T. confusum) is unable to use them to fly. The two sexes are similar in external appearance, i.e. there is no sexual dimorphism.
The eggs are 0.6 mm long, oblong in shape and whitish to nearly transparent in colour.
The larvae are elongate and approximately 6–7 mm long when mature. They can be distinguished from some other tenebrionid larvae by the last abdominal segment ending in two points (urogomphi). They are mostly yellowish-white except for: the dorsal part of the head, the tips of the claws and the tergites, which are slightly darkened; and the urogomphi and the tips of the mandibles, which are reddish-brown.
The pupae are initially white, but turn yellow after a day or two, then gradually turn darker.
In the wild, Tribolium occur under bark and in old logs. A number of species have adapted to living in stored plant products.
Tribolium lay their eggs in a food source such as flour. These hatch into larvae which proceed to feed and grow within the food, avoiding light. There are usually 7 or 8 larval instars, but there can be as few as 5 or as many as 11 depending on food, temperature and humidity. The larval stage can take 22 days to over 100 days, depending on food, temperature and species (T. confusum takes longer to develop than T. castaneum). Once development is complete, larvae come to the surface of their food or to some sheltered space or crack, where they become pupae. They use empty pupal cells left behind by Mediterranean flour moths when available. The pupal stage lasts for 5–12 days depending on temperature and light. Adults emerge from pupae to continue the next generation. Adults are among the longest-lived of stored product insects, able to survive for over three years. Males (but not females) can continue reproducing even after their third year.
The original distribution of Tribolium is suspected to be in the region of India, southwestern Asia and the eastern Mediterranean. The genus has since spread worldwide via human trade.
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