Well the chucks had a FL treatment today. The dusting I gave them had reduced the lice but not cleared them. I've had a really good scrape round the housing and no sign of the dreaded red mite, so hopefully that will sort all pest problems as they were wormed recently so covered all the bases.
When mine had red mite they were reluctant to go to bed and not seen that behaviour since but am going to switch to HF's house mite deterrant painting technique rather than use the red mite powder I have used in the past.
HF - if you read this, do you dust your birds at all or just treat them with insecticide as needed. Think I am going to struggle to get Ivermectin but FL is obtainable 
For red mite, which don't live on the birds at any stage of their lives, I just treat the house (not the birds) with one spray of a residual insecticide which lasts all year on a wooden house and I paint DE onto the roosts thoroughly on all surfaces. Also I paint in the corners of the nestboxes and house and any seams.
I never dust the birds at all. They should make their own dust bath which will keep they mostly free of lice and mites. If lice look like becoming bad I spray with Ivomectin but Frontline is equally effective. Apply to back of the neck. Both are similarly expensive and zap scaley leg mites, fleas and lice.
I used to dust nestboxes with Derris when you could get that but when that disappeared I used the Barrier products for RM & lice which I found very expensive and ineffective. I've tried many red mite sprays (such as Mite Kill?) which are also very expensive and not noticably effective and eventually bit the bullet and used an insecticide which did the job for a fraction of what I was spending on ineffective spot treatments.
DE helps once the RM are eradicated and it also makes scraping droppings off perches easy too. I don't like to dust birds or use loose powder in houses as dust particles in the air in a closed environment can irritate their air passages and also is a dangerous vector for viruses. Birds are paricularly vulnerable to respiratory infections.
Best wishes
HF