Oxford Bees

Varroa Count

Very high Varroa count for city centre hives

Submitted by will on Fri, 19/04/2019 - 06:34

I did a 24 hour Varroa drop count yesterday. This involves clearing the removable hive floor and counting the Varroa mites which drop out of the hive over a 24 hour period.

I counted

  • 15 Varroa on the floor of Colony 12;
  • 16 Varroa on the floor of Colony 4;
  • 30 Varroa on the floor of Colony 8.

These are very high numbers of mites for this time of year.

The modelling referenced by the National Bee Unit suggests that colonies starting the year with this many mites will be overwhelmed during the season. I'm not going to treat. I'll see what happens.

I did try to insulate 2 of these 3 hives before winter. The uninsulated hive had 16 mites. There isn't a noticeable difference in mite numbers between insulated and uninsulated which is counter-intuitive -- warmer internal hive temperature should encourage brood rearing which should give opportunities for mites to breed. This is a very small sample but I'm not seeing that correlation here.

Varroa fall is worryingly high for Spring

Submitted by will on Sat, 13/04/2019 - 19:38

I have seen a worrying number of Varroa bodies on the floors of my hives. This is particularly concerning at the start of the season because it suggests much higher numbers of the mites later in the season. If I was a conventional bee keeper I would treat the hives now. I'm not going to. We'll see what happens.

I periodically look at the removable floors in my out apiary in town. I've seen Varroa bodies on the floor of all the 3 hives there. I haven't been able to count the rate of fall yet but there were enough bodies to be a concern. There are also Varroa bodies in my hive in Headington. This afternoon I cleaned the hive floor and, 4 hours later, found 2 new bodies. This rate of floor is alarming.

The hives which contain colonies 8 and 12 were insulated with cork last Autumn. It wasn't the best job ever but it might have raised the temperature of the inside the hive so that more brood were raised. This would provide a great opportunity for Varroa to breed through the winter. I don't have evidence whether the insulation worked. I will try to count mite numbers to see whether there is a clear difference between insulated and uninsulated colonies. Colony 01 is uninsulated and has the very high mite count. Confusing.

Around the start of April there were also piles of dead bees outside the front of my hives in central Oxford. These were not fresh. It wasn't clear whether they died in the hive and were dumped by undertaker bees during the cold weather, or whether they crawled out. Either way it's not good news. Colony 8 had more dead than colonies 4 or 12.

I don't know what these bees died from. There were non-flying bees outside the hive on the ground. They could be suffering from a paralysis virus. There were no obvious signs of Deformed Wing Virus. I just don't know and I'm not likely to find out now.

No drama from my city hives

Submitted by will on Tue, 14/08/2018 - 16:51

There is very little to report from my hives in Oxford. They're bringing in pollen; there are Drones leaving and returning; there are very few Varroa falling onto the base board*; there are lots of wasps but none getting into the hives.

It's all very calm.

* maybe a dozen between the 4 hives

Varroa drop not quite zero

Submitted by will on Wed, 13/06/2018 - 07:18

Colony 13 is dropping Varroa. They are also cleaning out old comb so there is a lot of debris on the hive floor. I found 2 or maybe 3 Varroa bodies.

This colony is new to my apiary, having been established elsewhere. I haven't really included it in my Varroa Zero post because it's new. Hives D and G are included. There were no Varroa on the floor of either this morning. There doesn't appear to much activity in Hive D at all. I shall have to check them.

Varroa drop zero

Submitted by will on Tue, 12/06/2018 - 05:50

I regularly examine the floors of my hives. The stuff which falls out of the hive tells a story about what the bees are doing. I always look for Varroa mites. I've found none on the floors of any of my hives for several weeks. I don't know why.

Mites on the hive floor can indicate how many mites are living in the colony. Varroa live for between 27 days to about 5 months (source: Managing Varroa, National Bee Unit, 2017). The mites require bee brood to reproduce so it's not surprising that there are fewer mites in the early part of the year. What is surprising is that I'm finding no dead Varroa at all in well established and very active hives.

We had difficult weather in spring. The temperature started to warm and then fell dramatically. This led to a number of colonies dying of complete starvation or isolation starvation. Dead colonies don't support Varroa. Live colonies do, but only in cells with brood. I wonder whether this has interrupted the mite life-cycle and knocked them back. I do not expect to find any colonies where Varroa are entirely absent.

I have 6 occupied hives. Three of these are new colonies. I expect to have lower drop anyway because they arrive only with those Varroa which cling on to swarming bees (during the phoretic part of mite life cycle). I have one established hive where there is an Ant infestation. It's possible that the Ants are taking away the mite bodies. That leaves two established colonies which have brood but are dropping no mites. That's a small number of hives, but striking anyway.

There will be more to say about this later.

7 Hives at the end of the season

Submitted by will on Sun, 15/10/2017 - 20:28

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.

Mite Crisis in Hive E

Submitted by will on Tue, 12/09/2017 - 23:01

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 had hoped that the colony would be better able to manage Varroa. They've been untreated for a significant period of time. The swarm came last season from a feral hive in Barton.

Earlier this season they were very bad tempered which may be related. I should have checked whether they were Queen-Right (you bang the side of the hive. If the roar calms down quickly then they have a Queen. If not then they may be in distress and Queen-less).

I doubt whether replacing their Queen this year would have led to this situation. Even if she had no mite tolerance there would have been a time lag to produce vulnerable brood, and then a further lag to build up mite numbers. It seems more likely that this is the difference between mite resistant and mite tolerant. In the former there are hygenic behaviours or adaptations which inhibit Varroa mite reproduction. In the latter the bees just tough it out. I suspect that Hive E is only tolerant. We'll see whether it is tolerant enough.

Hive H showing very low Varroa drop

Submitted by will on Sun, 09/07/2017 - 19:44

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.

Hive F still shedding lots of Varroa

Submitted by will on Thu, 11/05/2017 - 05:53

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.