Whitefly. Safer's Insecticidal Soap or cold-pressed pure Neem Oil.

Al

cast skins of aphids.

As OP said, the white spots don't fly. That rules out whiteflies.

Beyond that, aphids are *far* more likely.

Yes, they never fly. I tried different times but they just stay there. They don't even move.

Jean, I am reading up on aphids now. What do you mean by "cast skins?" You mean those are not the aphids themselves but are the skins that they dropped?

When I first saw some insects, I actually saw something bigger and are pinkish, sort of transparent looking things. They looked like they were eating the gardenia flower buds. Later they disappeared. Now I saw these white things on the leaves. By this description, does it sound like it matches aphids better?

I will try to see if I can take a macro photo tomorrow.

Wikipedia shows some pictures of aphids, but they are brown and not pink. It is hard to just their size either.

Yep (shed aphid skins). Insects shed their outer skins (exoskeletons) periodically in order to grow. Aphid skins are cast about like dirty laundry.

Aphids come in many colors, including pink. Wanna see? Just click on the link below.

Look for different aphid species in green, gray, black, brown, speckled, yellow, and other colors.

Here is a link that might be useful: {{gwi:85885}}