The mealy bugs are gone now at least for another year. Fortunately, this year I only had about a dozen plants that showed mealy bugs this winter - not counting the seedlings. A few of them I gave up on and threw them out and the rest have been treated with BotaniGard ES and these plants are now mealy bug free. It is still possible that I may see these insects again, because I will likely buy some new plants. I try to treat all new plants even if they are symptom free. I have to say the hardest mealy bugs to kill are almost always from plants that originate in Arizona greenhouses. I suppose these mealy bugs are the progeny of generation after generation of mealy bugs that have become resistant to insecticides.

I had the most trouble getting rid of the insects of my Obregonia denegrii. The insects are able to hide in the structures of these cacti and avoid the BotaniGard. Keeping the plants wet helped because the stems swell up and open up the mealy bug hiding places. After about 3 weeks of wet growing medium the insects are all exposed and are finally easy to kill. The Obregonia denegrii seem to absorb water much more slowly than most other species. They will tolerate wet conditions for longer periods of time that cacti like Astrophytum, but it's much easier to kill mealy bugs on Astros without keeping them wet for a month.

Over the years I'm having fewer problems with mealy bugs now than five to ten years ago when I was using insecticides. I'm happy that there are organic alternatives.