Upon discovering stored grain infestation, immediate steps should include: 1) Isolating the infested stock to prevent spread. 2) Removing and disposing of heavily infested portions safely. 3) Cleaning the storage area thoroughly. 4) Applying appropriate fumigants or insecticides (if permissible and safe) to the remaining stock, following guidelines. Long-term preventive measures would be: 1) Ensuring grains are properly dried before storage. 2) Storing grains in airtight, pest-proof containers (e.g., metal bins, silos). 3) Regular inspection of stored grains. 4) Maintaining hygiene in storage facilities. 5) Using natural repellents or biological control agents. 6) Practicing crop rotation to reduce pest populations in the field, thus reducing initial infestation in storage.