What is primarily a problem of stored grain in transport?

The primary issue with stored grain during transport often involves rice and grain weevils. These pests are known for infesting whole grains, including rice, wheat, corn, and other cereal products. Weevils are particularly adept at penetrating packaging and can thrive in stored products under suitable conditions, causing significant damage to food supplies. Their life cycle allows them to reproduce rapidly in grain storage facilities or transport containers, making them a persistent and challenging problem.

In contrast, while other pests like Indian meal moths do affect stored products, they typically cause damage to processed goods or cereal products rather than whole unprocessed grains. Booklice and clothes moths are less commonly associated with stored grains specifically, with booklice preferring damp environments and decomposing organic matter, while clothes moths primarily target textiles. Thus, the focus on rice and grain weevils as the main problem during transport of stored grain is justified by their specific habits and the damage they cause to grain itself.