I know I keep banging on about red spider mite, but it is decimating my brug collection and having a cold wet windy May hasn't helped the situation.
These are three I planted last autumn. The one on the right has Ys the one on the left has branches, so although all the large leaves have dropped off and the colour has drained from the new growth, the stems are strong, and hopefully all is not lost.
This is a rooted cutting I bought which is doing well, but the lower leaves are showing signs of red spider mite, so I expect all the leaves will whither and perish before long.
Zone: This is England we don't do zones. Pick any number between 2 and 11
Can't you spray them? If you want to be careful of chemicals, could you use an insecticidal soap? My first defense is either a little Listerine or baking soda with a dash of dishwashing soap and/or maybe a dash of cooking oil in a sprayer, fill with water and hand spray.
Hope you find something. I have a couple Brugs and I really like them.
Oh how sad! Do you spray them at all for the spider mites? I don't know anything about either the mites or brugs, but tha's really sad to see your poor babies!
Are they outside yet? The best solution for red-spider-mites I've found is to keep the Brugs where they can get rained on, and at other times, the foliage misted (top and bottom as possible). The pests hate that, preferring hot and dry conditions.
I've found this problem starts on the tender new growth also, not on the older bottom leaves... but might well be, nonetheless.
Gruntfuttock Here is what I would do if these were mine. First move the good one away from the others!
Second strip off all the leaves on the bad ones and the lower on the good one. Then I would find a sprayer and put hot water in the sprayer with some 70% isopropyl alcohol and dish soap. I would spray the plants completely and soak the soil too. Some mites are harder to get rid of than others but the hot water is the main way to rid the hard to kill ones. I use my steam clearner on our or the flying insect RAID in the blue can held 16 to 18" away so you just mist the plants. You will have to do this on a regular bases until you see the leave form correctly or toss the plants and start over? Wishing you the best of luck and spray them on a weekly bases to keep them healthy. The key is to keep them healthy and these aren't for everyone to grow unless you can properly care for them and not neglect.
Karma, they may look neglected, but I can assure you I have given these plants more TLC than any other plants I own. Spraying the tops and bottoms of every leaf three times a day takes time, but I did it for months throughout the winter. Plain water, oils, cigarette butt soaked water even.
I have recently bought a vial of Phytoseiulus persimilis which are predatory mites, and why the plants are in the conservatory.
The three outside had such a bad infestation I moved them there despite the fact it was colder than I would have liked, then overnight the wind got up and ripped the large leaves off.
I'm a bit worried about using the steam cleaner on them.
My next attack will be to remove the affected leaves and spray with bifenthrin.
Zone: This is England we don't do zones. Pick any number between 2 and 11
I was just reading in our Ohio agricultural site and they highly recommended predatory mites. Never would have thought of that. I should have known that you already tried simple spraying.
Thanks for the heads up and I will check for spider mites now and again. Best of luck.
Gruntfuttock, I know you take great care of your plants but there are folks out there that see a plant and have no clue as to just how much care these plants need. Yes, try the steamer and you will need to hold it back about 8 " to 10 " so you don't burn it. I have found just a few uses of the steamer and all is gone. I also use this to clean pots and the greenhouse walls.
Gruntfuttock 
Wishing you the best of luck and spray them on a weekly bases to keep them healthy. The key is to keep them healthy and these aren't for everyone to grow unless you can properly care for them and not neglect.