What insect pest is known to commonly infest stored grains and products?

The Indianmeal moth is the correct choice because it is a well-documented pest that specifically targets stored grains and processed food products. This moth is recognized for its larvae, which feed on a variety of grains, flours, cereals, and dried fruits, causing significant damage and contamination. The adults are small moths that can often be seen fluttering around food storage areas, and their presence usually indicates an infestation.

In contrast, other pests like the housefly are not specifically associated with stored grains; they can be found in various environments but are more generalist feeders. Ants, while they can invade pantries in search of food, do not have the same specific association with stored grains as the Indianmeal moth does. Termites primarily feed on wood and cellulose materials, making them irrelevant in the context of stored food products. Therefore, the Indianmeal moth stands out as the primary insect pest linked to the infestation of stored cereal products.