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  • Oxalic acid time. What do you plan to do?

  • Honeybee pests and diseases.
Honeybee pests and diseases.
 #1712  by Jules59
 19 Jan 2019, 19:31
Hi Jim
I missed off the first winter VC count.
These are the daily drop rates and treatments for the "bad" hive:

16/12/2018 VC 14/day (over prev 7 days )- then treated with Oxalic acid
27/12/2018 VC 65/day (over prev 7 days )- advised to repeat VC in a week
06/01/2019 VC 36/day (over prev 7 days )- then treated with 2nd dose Oxalic acid
19/01/2019 VC 3.6/day ((over prev 7 days) - wondering what to do now !

I was advised not to treat either hive in Autumn as VC were <1/day. (NBU Calculator also suggested not to treat but to observe in several months). In retrospect I think that was a mistake.
 #1713  by Patrick
 19 Jan 2019, 21:31
Hi Jules

Personally I would not trickle 3 times consecutively . As Jim suggests I would leave until early spring and use another treatment if still concerned.

I like the principle of only treating when proven necessary (IPM) but sadly the mite drop test seems quite unreliable as a means to extrapolate to the total population, probably for reasons we won’t go into here, but you are discovering the issue. I also found I became obsessed with numbers without being sure what they were really telling me.

As such, missing treatment at the end of the season on the basis of drops is risky as it leaves you with a potential problem later at a time when treating options are limited by likely ambient temperature.

The drops you are recording are following treatment so are likely higher anyway (killing mites is the point after all).
 #1714  by Jules59
 20 Jan 2019, 00:01
Thanks Patrick.
I will leave off further oxalic acid trickling and wait to see what transpires.
I agree with the mantra; treat only when necessary. But learning how to decide is not easy.
 #1715  by NigelP
 20 Jan 2019, 11:23
Jules59 wrote:
20 Jan 2019, 00:01

I agree with the mantra; treat only when necessary. But learning how to decide is not easy.

Unless you are doing sugar rolls or alcohol washes it is very difficult to estimate varroa numbers from drop counts.
They can give very misleading information. For example several times I have had hives dropping very little through an open mesh floor, yet one oxalic acid vaporisation later there are 1000's on the board. Varroa can catch you out time and time again and are IMHO THE biggest killers of hives of bees. Either through weakening them or DWV which has become more virulent (in most cases) since it has been using varroa as a transmission vector.

My policy is to treat as often as I can every hive in my apiary at the same time. MY preferred method is OA vaporisation with a sublimox which is very efficient. Even then I get hives that are mite bombs...and I can only really tell this by the drops after vaporisation. I'm not sure I agree with allowing parasite numbers to increase to a level they require urgent treating. Far better, IMO, to try to keep numbers constantly low in all hives by treating at regular intervals regardless of what the "drop counts" are telling you.
Why would you want to let parasite levels increase to the point where they need urgent treatment?
I often use the analogy of worming my cat at regular intervals whether he needs to be wormed or not. Rather than waiting for evidence of worms before doing so. He is now a hale and healthy 15 year old who still eats most of the voles (parasite vectors) that he frequently catches.
 #1718  by Jim Norfolk
 20 Jan 2019, 13:27
The question is when to treat. Is it every time you see a Varroa you resort to shock and awe and blast every hive or should it be done at critical times with a watch kept the rest of the year? The critical time is autumn that is when Varroa numbers seem to multiply for some reason just when you want healthy winter bees to be reared. There are now plenty of products to choose from and using one of the milder ones such as thymol will not only protect the bees but confirm the extent of the infestation. I have found very good agreement between mite drop counts and drop after Apiguard.

The other important time is at the end of the year to knock Varroa numbers down as low as possible so the bees have a healthy start in spring. The treatment of choice is oxalic acid. The agreement between mite drop and post acid drop is not nearly as clear mainly because mite drop depends on mites emerging with brood and being dead or weak. Healthy mites are less likely to drop and hang on to their hosts. Broodless colonies may have a lot of mites but drop very few. So mite counts are unreliable at Christmas.

The post oxalic drop also varies. Most have a peak drop on the first or second day which then tails off but some go on droppping mites for upto 2 weeks with the odd cluster of mites dropping much later. Jules numbers are interesting in that with a drop of 14 per day pre treatment there would be a lot of mites and this shows up in the 65 per day dropping over a week later. There were still 36 a day dropping two weeks later. The second treatment resulted in a daily drop of 3.6 a week later which suggests there were many fewer mites at the time of treatment. Quite why mites went on dropping for so long after the first treatment is one of those mysteries bees like to present us with to keep us guessing and show we don't know everything.
 #1726  by AdamD
 20 Jan 2019, 19:30
Jules, I think I would leave until spring and check then.

I treat in late summer using thymol (autumn is too late) and generally treat with oxalic acid when I assume the colony to be broodless around the shortest day of the year - so between Christmas and New Year is convenient as I am off work at that time, and from my experience, the mite drop almost always peaks a couple of days after dribbling and then decreases - after a week or so, there is nothing worth counting and I usually take the mite boards out.
It is generally advised to dribble just once (you can vape more often) so I would not repeat the process but check the colony in spring. When I have done the odd MAQS treatment or Apiguard in spring on any colony I have been concerned about, I have seen few mites fall.
 #1728  by Jules59
 20 Jan 2019, 22:11
Thanks everyone.
My plan now is review in the spring (end of March) and consider MAQS. Then treat with Apilife Var (Ive already got some of that) in Aug/Sept.
Fingers crossed.
Jules
 #1730  by NigelP
 21 Jan 2019, 09:23
AdamD wrote:
20 Jan 2019, 19:30

I treat in late summer using thymol (autumn is too late)
We don't come back from the moors until mid to late September so Thymol treatments are out as it is now far too cold for them to work effectively. So It's Strips or OA. It's late but no choice if we want a heather harvest. Fortunately winter bees are still being born into November around here.
 #1731  by Patrick
 21 Jan 2019, 11:19
Interesting to read that Samuel Ramsey in the States reportedly found that varroa preferentially feed on bee fat bodies rather than simply haemolymph, as previously widely assumed and will move over the bodies of mature bees to specifically feed on the fat reserves localised within the underside of more mature bees.

Made you wonder about longer lived so-called winter bees, which are particularly known to develop larger fat bodies in the Autumn as a longevity colony overwintering strategy and the particular impact on them of large numbers of phoretic mites.

Puts effective late Summer / Autumn treatment into renewed perspective.
 #1733  by Jim Norfolk
 21 Jan 2019, 13:39
Interesting point Patrick. I wonder whether an increased availability of fat body material to Varroa accounts for the marked increase in mites end of summer and into autumn. Better nutrition leads to better quality Varroa eggs and resulting increased survival of stronger offfspring.