Little white bugs can be a definite problem!!! It is probably mealy bugs or a spider mites and this does cause leaf yellowing and dropping in many plants.

According to the web, you probably need to treat your plant with an insecticidal soap that specifically targes the mealy bugs or spider mites. You may need a little help on this one from your local nursery since lucky bamboo can be a little sensitive.

Perhaps your plant has also been subjected to a sudden change. If the plant is exposed to too much sun it may turn yellow. Do you have this plant in direct sunlight on your desk? Is your area prone to drafts at night or does the temperature get cold? Too cold of temperatures may promote yellowing. If a stem is infected it will turn yellow too. Are there any signs of strange growth such as white or other colors of blotches?

Here is a link that might be useful: Mealy Bugs and Spider Mites