Two weeks ago, when fixing brown basmati rice for dinner (bought from bulk in last 2 months) kept some in a kitchen container, noticed black "dust" at bottom of container. Put on eye glasses to see - eek!... many dead teeny tiny black bugs, but about 200 crawling actively. Threw the whole amount out. Now - today - preparing white rice (bagged, different brand, purchased within last 4 months) from similar kitchen container I use for daily use... and eek! again the bottom coated with black "dust" and about 10% crawling teeny tiny black bugs. Will the remainder not placed into plastic container be be okay in the original bag? Or should the BAG be thrown away? How can I prevent this in the future?
There could be 2 sources of the pantry pests you describe. You could be bringing them home in products from the store, or they have infested your cabinets and are spreading to the new products you bring home.
Here is a good publication that has pantry pest control at the end, after describing many of the little critters in detail: Insects in Your Food & Pantry. I would go right to the last page for control measures. Freezing 2-3 days will kill the existing pantry pests but then you need to make certain the products are stored in airtight containers that the pests cannot get into so there is no re infestation. Package any new products you bring home well. The packages they come from the store in are inadequate for protection from pantry pests. Glass jars with screw on lids, heavy plastic containers will work, but plastic bags and card-board boxes will not prevent infestation.
Be sure to clean the cabinets well. Vacuum any spilled food dust from the corners and cracks and check animal foods for contamination , too. They could be spreading from dog food or bird seed.