The grain weevil is responsible for major losses in weight and nutritive value because it bores into the grain and feeds on the endosperm. This reduces the weight of the produce and lowers its nutritive value. These insects also lower quality by contaminating the grains. Mouldy grains are frequently found during storage and in the market places in tropical Africa, where the high humidity and temperatures are favourable to the growth of mould. Because protection of grains in storage, transportation, and marketing is negligible, mould infestation of most cereal grains and legumes is high.
Rodents are also responsible for large losses of grain.
Large numbers of rodents, mainly rats, are found in the markets of West Africa, where they feed on the grains and contaminate them with their urine and feces. This means that in addition to the reduction in quantity, there is also deterioration in quality of the grain. Poor handling of grains also leads to spoilage and contamination with dirt. Because the protein-rich legumes grown in the country are infested and ruined in storage, the importation of canned baked beans, green peas, and a host of other legume products is now the rule in many African countries. Clearly, the metabolic changes that occur in food crops cause a reduction in their nutrient content and therefore become a loss to the consumer.