The only time I had mealybugs was in a terrestrial utric. I submerged the plant under water for two weeks. This drowned both the mealybugs and the newly hatched bugs. The problem with mealybugs is that they can get in the soil, and once there they can be very difficult to extricate. I was fortunate to have a plant that didn't mind being flooded occasionally. I'm not sure this would work with your plants. It is better to lose one plant than an entire collection.