- If they are worm like then they are not root mealy bug. Those guys are white, largish and round. You normally don't see them until you re-pot the plant or it is a terminal infestation.
- Aphids live on the plant not in the soil
- soil dwelling insects like fungus gnats (dark, mobile) and springtails (brown or black and jump around) and others can usually be controlled with soap and water.
Put a tablespoon of dish soap in a quart of water. Put the plant in the sink, pour mixture through. Wait five or ten minutes and flush with clean water.
If that doesn't work you can try what I call the "big hammer" approach: one tablespoon of bleach, one quart of water, pour in, wait and flush with clean water. Be warned that this is a last resort as many plants respond poorly to this treatment
Edit: water mixed with soap will clog the breathing holes (spiracles) of insects. A few minutes not being able to breathe is sufficient to kill most insects. Eggs, however, will survive and hatch again. A second application of soap mixed with water after another five to seven days might be required