My orchid has mealybugs, what should I do?

It's not as serious as it looks, mealybugs are pretty easy to control if you act fast. The simplest thing is to wipe each leaf and stem with a cotton pad soaked in alcohol, touching the bugs directly when you see them - it kills most of them right away. If the infestation is heavy, you can spray with water and neutral soap every three days for a couple of weeks, or get an insecticide specifically for orchids from any nursery. Isolate the pot from other plants in the meantime, because they spread easily.

Scale insects are more of a pain than they seem because they reproduce fast and alcohol sometimes doesn't reach the eggs hidden underneath the leaves. I had an orchid a while back that seemed under control with cotton, but they came back after a couple weeks, so I ended up using a systemic insecticide that works better - you spray it once and the poison circulates through the plant for weeks, killing the pests as they hatch from the eggs.