The cadelle is a black beetle that is larger than most stored product beetles being about 1/3 inch (6 to 11 mm) long. It has a flattened body and may resemble a ground beetle (Carabidae) to an untrained eye. The key identifying character to examine is the point where the prothorax joins the elytra (wing covers). On the cadelle, a visible space is present between the prothorax and wing covers and part of the mesothorax is visible. In most other beetle, the prothorax touches the front edge of the wing covers forming a thin seam.
During the time of larval development, a single cadelle is capable of significant destruction of grain. One study showed that a single larva can destroy the germinating power of 10000 grain kernels by itself because it feeds only on the germ portion of the grain – it being the softest part of the grain. Cadelle larvae also can be serious pests in tobacco facilities where they bore into tobacco bales in search of insect larvae on which to feed. Small cadelle larvae can survive on tobacco leaves for a short while but will die unless insects are available. The larvae may survive for two to three years in tobacco, thoroughly ruining the bales by their boring activities.
Cadelle larvae cause damage to wood storage bins by boring into them to pupate. New grains and tobacco can be infested by adult beetles emerging from the sides of the storage bin after the previously infested grain or tobacco has been removed. Larvae seeking pupating sites also have ended up in such strange places as books, balls of twine and carpet rolls.
Adult cadelles are voracious predators of the larvae of other insects found in grain and will kill any larvae they encounter, in particular those of the Indian meal moth and the sawtoothed grain beetle. Adults avoid light and if brought to the surface of infested food material, they quickly tunnel back out-of-sight. They hide in the corners and folds of boxes and bags and in the cracks of storage containers. Adults also bore through paper and cardboard packaging and into wood pallets and storage bins creating significant damage.
All stages of cadelles are active during the winter in heated buildings. Eggs and pupae are susceptible to cold temperatures and may perish. Adult cadelles are more tolerant of cold than are the larvae.
Biology and life cycle
The cadelle is a cosmopolitan beetle being a pest of stored grains throughout the world. It has been nicknamed the “bread beetle” because of its habit of cutting the silk bolting in flour mill machinery.
The female cadelle lays her eggs loosely in flour, grain or other food product in batches of 10 to 60 at a time. In her long life of up to one year or more, the female may produce hundreds of eggs, up to or more than 1000. Cadelles also have been observed to pack their eggs into crevices where they conceivably will be more protected. The larvae develop for a period of 38 days to more than one year, depending on conditions. Two generations are likely in a single year with three generations in tropical areas.