If you have mealy bug on one plant in the house, you probably have mealy bug on ALL PLANTS in the house. Treat everything, even if you don't see any obvious mealy bug. There are a number of pesticides that do work, read labels, follow directions.
When I was running a 1200 orchid plant collection, for mealy bug and most insect outbreaks I use a cocktail, meaning all components mixed together in a 5 gallon bucket of water. I used Decathalon - a synthetic chloronated pyrethrum compound, Enstar II - a juvenile growth hormone disruptor, Pentac 2 for spider mites and a few drops of spreader-sticker - a soap to help bring everything into solution. So the active ingredients were Decathalon, Enstar II, and Pentac 2. This cocktail "cured" about everything. Though I would have to apply twice, 10 days apart, in order to get full control.
Spend time reading labels at your local nursery supply. Malathion is the 1960's era front line killer for mealy bugs. For a while the mealies were developing resistance, Malathion went out of favor. Now, 60 years later, most farms and Ag businesses have moved on to other compounds, the resistant strains have largely died out and Malathion now works pretty well in most regions, because the farmers are not using it.
But there are several pesticides that list mealy bug on their labels. There are at least a half dozen different "mode of action" pesticides you can use. Check Bayer products, Check ortho products and check Bonide brand products. See which ones list mealy bug.
Somewhere on the label there will be a number for "Mode of Action Group". Try to find 2 products with different "Mode of Action" numbers, then you can alternate between the two and have a better chance of killing off all the bugs without developing resistance.
Bonide brands tend to be less expensive than Bayer, they are the "generic" producer of trademark pesticides.
