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Newly emerged larvae are able to develop on visibly undamaged grains (Roorda et al., 1982) and the larvae prefer the germs of grains for feeding.
Infestation by adult beetles can be readily observed by the tunnels they leave when they move through the flour and other granular food products. Damage is particularly serious in grains such as rice and wheat, which have either been dehusked or processed into other products. When infestation is severe, these products turn greyish-yellow and become mouldy, with a pungent odour.
Infestation may also be apparent by the appearance of adults on the surface of the grains.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
Both the larvae and adults of T. castaneum damage the host. They cause extensive damage to grains already damaged as a result of handling during harvest (Atanasov, 1977; White, 1982), holed grains, and those damaged by other pests.
A single T. castaneum larva was shown to cause a mean dry weight loss of 12.3 mg, in laboratory tests on millet, at 28°C and 10% RH (Roorda et al., 1982); at 70% RH, the loss was 7.9 mg.
In Nigeria, weight losses of 29.5 and 39.2% were reported in 4.5 months for dried yam chips that had already been in storage for 6 months (Adesuyi, 1980).
T. castaneum infestation of stored sunflower seed resulted in weight loss, contamination with faecal pellets (Vargas Piqueras, 1979), and an increase in the acidity index of the extracted oil, especially from highly infested seeds. This resulted in oil of reduced quality.
The larvae of T. castaneum feed primarily on the germ of the cereal and render the damaged grains unfit for sowing (Khanna, 1977).
In India, T. castaneum was one of the most important pests of stored cereals, millets, pulses and oilseeds recorded by Tripathi et al. (1999). In West Bengal, T. castaneum, Sitophilus oryzae and Rhizopertha dominica were common pests of stored wheat and rice, causing grain damage ranging from 4.3-21.8% at Purulia, 6.4-25.5% at Kalyani and 4.5-22.2% and Cooch Behar on wheat; and 3.0-15.5%, 4.7-23.4% and 4.4-20.4%, respectively, on rice in these areas.
Insect pests of stored products such as T. castaneum not only reduce the germination of wheat grains, they also contaminate the wheat (Khare et al., 1976). A high level of excrement contamination gives the flour made from the infested grain a dirty appearance. The species of insect feeding, and the resulting chemical changes which occur, cause an unpleasant taste in bread made fom such flour.
Repeated consumption of contaminated material probably constitutes a health risk to both humans and livestock. Wheat flour infested with T. castaneum, T. confusum and T. molitor was toxic to mice. Morphological and histopathological studies indicate that the toxic symptoms were probably due to defensive secretions of benzoquinone compounds produced by the insects (El-Kashlan et al., 1997).