The Vaad of Denver reports that there has been an increase in reports of infestation in fresh iceberg lettuce.
For pre-washed bagged iceberg lettuce, it is now recommended to check 20% of the bag. If no insects were found, you can use the rest of that bag without further checking. If insects were found, check the entire bag.
Alternatively, you can soak the entire contents of the bag in soapy water, agitate it and then soak it in plain water, then pour the water through a strainer lined with a white cloth, place the cloth on a light box and inspect it for insects. If no insects are found, it may be used. If insects are found, repeat this process. If insects were found after the second time, discard. For heads of iceberg lettuce, discard the outer leaves. Check the next 5 layers (10 leaves). If no insects were found, you can use the rest of that head without further checking. If insects were found, check all the leaves.