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.
One hive (C) was so wet with condensation that it was impossible to tell what had fallen to the floor. There must have been wax and pollen. Presumably mites but it was hard to tell. The hive is ventilated but I assume that there has been a strong honey flow and the ventilation has been insufficient.
One Hive (E) was in crisis but activity seems much reduced. Fewer mites and fewer hatchings. This might mean that the crisis has abated or that the colony is in deep trouble.
The overall picture is that foraging is still strong during the warmer parts of the day. Brood rearing is strong which is supporting very high levels of mites. This picture is matched by Hives A and H in Headington. A is dropping lots of mites. Both A and H are bringing in large amounts of pollen. H is building lots of comb (which A doesn't need to do).
The Varroa population models suggest that colonies risk collapse when total mite numbers is greater than 1,000. I would only be confident that hive H has fewer than that.
What happens next? This is where my commitment to no-treatment beekeeping is tested.