I visited my out-apiary today and examined the removable hive floors for evidence of recent activity.
Three hives (D, F and G) show evidence of recent brood emergence. There were also hundreds of dead mites. Hive D had been especially prolific. There was also crystallised sugar which suggests that old honey is being eaten or cells are being cleaned out.
Hive E is having a Varroa mite crisis. I checked today and for the previous 2 weeks. Each time I found hundreds of dead Varroa mites.
High mite drop can be a factor in colony collapse. I don't expect them to perform well next season - if they survive through the winter. I expect them to be weakened, and any brood raised in early spring will be heavily infected with Deformed Wing Virus or other diseases symptomatic of Varroosis.
I moved Hive H from my garden to my out-apiary on Friday 30th June. I looked at the removable floor today and found 1 Varroa mite. Just 1 in 8 days. Compare that to Hive H which was dropping 20 per day as a new swarm.
The colony in Hive H has been feral for some time. The colony in Hive F had been a standard bought Buckfast queen 2 or 3 years ago. It's possible that the feral colony is adapting to Varroa and has managed to limit its' numbers. The mite is still present - it's endemic and won't now go away.
I'll see how Hive H fares as it settles in.
I looked at Hive F's removable floor again on Tuesday 9th May. I counted 24 Varroa mites which had fallen out of the colony. That's 8 per day. Will they survive?
UPDATE: I visited the hive on 12th May after dark. There were another 32 mites. I've counted 88 mites in 7.5 days, an average of about 12 per day. That's very high. This colony has been untreated for a couple of years but it was from a bought queen before that. I don't think much of its' ability to manage Varroa.
I put the a swarm from Helen into Hive F on the evening of 2nd May. I had a look at the entrance and the removable hive floor this morning.
The colony appears to be settling in well, despite the colder May weather. There is shed wax on the removable hive floor; there are bees coming and going. It appears that they've been building comb and orienting themselves to their new area. I didn't look for pollen, but I wouldn't expect to see it this soon anyway.
I'd expected that the new bees would bring Varroa. Today I found a dead mite from the colony which I hived earlier this week. It was on the floor of their hive.
The feral colony from which both casts came has apparently been there for 3 years. Today I could see their entrance which had lots of activity. It would appear that they are very strong despite this infestation.