Mealy bugs and other unwelcome guests...

[cbuchman]

I find that when I summer my orchids outdoors, I usually don’t have too much difficult with mealy bugs, more with scale. I try to not bring any critters indoors in the fall and keep a wary eye out for any hitchhikers. Things stay quite through the winter, and then I typically experience a bug bloom in the spring when the greenhouse starts to get warm. Then I realize notice an increased population and become very vigilant

[naoki]

I could control mealy bugs with repotting+spraying Dyna-Gro Neem Oil to the entire plants. But I had to repeat spraying and watering with diluted Neem a couple times, and it is a slow process. If you want to remove them quickly and effectively, Merit, which Ashby suggested, should work better. The active ingredient is Imidacloprid. There are others with the same active ingredient. For example, my neighbor grocery store has Bonide Systemic Houseplant Insect Cotrol for $7 or so. Bonide

I think that Bayer also makes something similar, but with a higher concentration.

But if your infestation is still minor, and you don't have lots of infested plants, more labor-intensive, organic methods may be good enough with lots of patience and time.