Mealy bugs on cactus

I have a chronic pseudococcus problem, at least my cacti do, I've had the little beasties since I missed them on a purchase. I over winter the cacti in the house, drier and a touch warmer than the greenhouse, come springtime they migrate out to the greenhouse. What I have observed is that the pseudococcus spread and proliferate as things warm up in the house. However, within a few days of moving to the greenhouse there numbers are significantly reduced and they continue to dwindle. On returning to the house the next autumn the numbers slowly increase accelerating as spring approaches.
Has anybody else observed this type of effect?
Is it due to climatic conditions?
Or does the healthy ant population in the greenhouse have a role?

 

I went for years not actually knowing what one of these was, never came across them, but now they are a real pain.
I tend to brush the ones I see with meths, but on repotting some Aeoniums the other day I noticed them actually in the soil, so total eradication seems almost impossible.

 

Possibly. When it is cooler the outer flesh of cacti and succulents is that little bit softer thus easier to feed off.

 

Goi the feeling Nigel is saying the opposite happens?

I only find them a problem in the conservatory that is kept warm, or near room temperature all the time, in the greenhouse they rarely exist.

Am I right in thinking this is a mainly tropical pest, or at least one that likes constant warmth.?

 

Bang went that theory!