I have been battling with mealybugs for over 2 years now, they're always coming back. I'm getting tired of the hassle of constantly having to spray the orchids, so I tried something else.
One of my friends in the Netherlands works for a biological pest control company, and as a gift she gave me a jar of
Cryptolaemus montrouzieri larvae (a type of coccinellid). These bugs are amazingly effective, they cleaned up the worse of the mealies in only a few days and are now scouting the plants for lone mealies. The funny thing about these larvae is that they look just like mealies, only hairier. I think that this method works so well that I'll be buying some new ones every few months (they'll live about 5-6 weeks unless they reproduce, which is rare on long tailed mealy infestations) as permanent mealy population control, or maybe I'll try using parasitic wasps.
Just thought I'd share this for people that may be interested to biocontrol. Here's my friend's company website with some info.
entocare.nl