I haven't mixed the DE in with the rice, but I did have a similar problem with bugs in everything - Indian meal moths, specifically. I threw all the non-canned food out,even if it had never been opened, and emptied every single kitchen cupboard, removed all the shelves where possible (so nothing could hide in the crack between the back or side of the shelf and the frame of the cupboards), disinfected everything, etc. Then I dusted the cupboards in DE, and put bay leaves on all the shelves (they apparently help deter bugs). For canned goods, I removed all the labels and threw the labels away (anything paper or cardboard had to go as it can harbour the eggs), washed each can, and just wrote on the cans with indelible pen so I'd know what was in it. Every new food item that came into the house in cardboard or paper packaging was placed in the freezer for 48 hours (inside ziplock backs), and then the contents were put in glass containers.
I also, by chance, discovered the source of the problem did not travel in on food - they had come in inside a cable box which had just been installed - I was vacuuming the living room a day or two after noticing bugs in the pantry, and saw the worms crawling out of the box en masse! I sprayed the thing with insect killer and insisted cable come and remove it. I later read they sometimes nest in the cardboard packaging, so if you recently got anything new in cardboard boxes - computers, tv, etc - be sure to check around that area. They hatch out into worms, then moths, make their way to the food cupboards and lay more eggs.
I still freeze every food item that I buy in paper or cardboard - flour, sugar, boxed goods, etc - for 48 hours before emptying the contents into glass jars, and I refresh the dried bay leaves every month or so, and have had no further problem.