Dr Frazier from Penn Stat Uni. is giving some interesting lectures at the BBKA convention which touch on some of these subjects.
Details on the web site.
Dr Frazier from Penn Stat Uni. is giving some interesting lectures at the BBKA convention which touch on some of these subjects.
Details on the web site.
Yes, I was a bit mystified as well - so my visual image is:Originally Posted by Geo224
... Splits and artificial swarms involving the transfer of at least one comb of brood promotes horizontal pathogen transmission. Horizontal transmission selects for pathogen virulence. Natural swarming involves vertical transmission which selects against pathogen virulence. ...
Can anyone translate into English please?
Horizontal pathogen transmission in artificial swarms - so one box next to the other on a horizontal plane (don't think about splits by placing one box on top of another!). Pathogens move horizontally. With a swarm they fly up in the air - so vertically - and fly away from their problems - therefore 'virulant' (but probably wishful thinking). I'm probably wrong.
Kitta
We're the bad guys - again!
No, something else. David is trying to be smart, and failing miserably. Vertical transmission in my book is a pest going mother to daughter. Horizontal means jumping from individual to individual. Think of family trees. In this case the individuals can be colonies.
There has been speculation, and I believe it to be wrong, that mites will evolve into a less virulent form and that vertical transmission encourages that. My view is that it is always in the mite's interest to be virulent. Any evolution towards a less damaging relationship will come from bees becoming more resistant.
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I recall working with a lady of an uncertain age, who had long wispy hair and wore floaty dresses - something that was unusual in that particular workplace. She was extremely well spoken and gave the impression of being remarkably erudite, so much so that she was intimidating. Nobody really questioned either her qualifications, her ability, or her slightly unusual, offbeat, ideas because she said they worked and offered her own proof.
It was assumed she was bona fide because of the way she behaved. Meetings almost always ran to her schedule, she would tolerate no interference, no challenges - she had to have her say, had to tell everybody else how it shoudl be done. She had her own agenda, which she ruthlessly followed and managed to talk herself up at every opportunity, whilst the rest of us just carried on doing things the way we always had - because it worked.
She didn't move up the ladder either high enough or quickly enough, so left and set herself up as a private expert, with long words gushingly advertising her expertise (and whacky ideas) as well as her previous experience. To begin with it all went well, money rolled in. But, a bit like the emperor's new clothes, the word got out and prospective customers were able to see through the carefully created mirage and found there was nothing there except a lot of big words and empty talk. Her business collapsed.
I've tended to lean towards the opposite opinion. A parasite that kills its host ultimately fails though equally I also think that over the past decade or so until the past few years and a move to IPM rather than silver bullet treatments that we've ultimately selected for more virulent varroa.
From a practical point of view though, how do you select less aggressive varroa opposed to more resistant bees? Ultimately I wonder if the two go hand in hand.
As far as David Heaf's comments go, the mother to daughter transmission (vertical) takes place with natural swarming just as much as with controlled artificial swarming. He's plain wrong. Horizontal transmission describes mites leaping from colony to colony, almost always on a bee. So Varroa has both, but the spread around from colony to colony is mostly horizontal.
As to whether avirulence (less prolific types) can arise in Varroa (rather than an equilibrium be reached when the host gets better at suppressing the parasite), I just don't see how there will be selection driving that to happen. The issue I have with that idea is that any less virulent mites arising within a colony (eg by mutation) will always be outcompeted by her more virulent sisters. The competition within a colony will always cause avirulent types to be suppressed, so the advantage to the mite of 'allowing' the colony to survive never gets the chance.
There is one way this might happen. If mites develop that are competitive with their sisters but somehow do less damage to the host then the host colony may survive longer and the mite therefore be 'more successful', enhancing its chances of surviving and spreading. That would be a mite that doesn't multiply and spread the viruses that cause colonies to die out.
So ... if beekeepers didn't treat (the idea is attributable to a whole range of people like Klaus Wallner, Albert Knight, John Dews, John Kefuss, and many many others rather than an argumentative simplistic and attention-seeking joiner from Essex!) then there is one thing that might happen (slowly): mites get better at not passing on viruses.
There is, of course, a means of testing this hypothesis. We now have a prediction, and there is a great big natural experiment out there. I know that there is appropriate expertise on the forum. So .... the mites on Apis cerana, are they better at suppressing A. cerana viruses than V. destructor is with A. mellifera? I could see a small theoretical paper in Apidologie on this .....
One complicating factor. It is probably to the mite's benefit to be more resistant to the viruses. That would mean that the mites would evolve in the direction of virus resistance anyway, even without a benefit tot he host colony. Maybe V. destructor just hasn't come to terms yet with the viruses it has encountered in Apis mellifera, whereas V. jacobsonii has had plenty of time to learn the tricks to be less affected by the viruses in Apis cerana.
Is anyone still with me? Should we shift this to Bee Health?
G.
Vertical transmission resulting in reduced reproduction of varroa.
Thomas Seeley looked at this phenomena in his study of bees in the Arnot Forest -for some reason IE isn't finding a link to it but I'm sure that it's still available online. One of his suggestions was that the mites had developed a reduced reproductive rate to cope with their lack of opportunity for horizontal transmission. Worth a read.
edit: bees from the Arnot Forest moved to an apiary with a corresponding number of New World Carniolan colonies showed no difference in mite loads to the Carniolans.
Last edited by prakel; 19-01-2013 at 10:47 AM.
Yeah, I was avoiding mentioning that Tom Seeley suggested this as a possible mechanism for his findings of colony survival in Arnot Forest. Seeley is close to God status in my eyes, and I think that he's wrong as I just don't see how that can happen when colony to colony transfer is so high and there is no obvious way that avirulence can dominate within a single colony. That makes me nervous (contradicting Seeley). Here is the paper:
https://www.beesfordevelopment.org/uploads/seeley_apidologie_2007(38)19-29.pdf
I haven't read the Büchler and Milani papers that he cites, but my guess is that is bee resistance rather than mite avirulence.
Last edited by gavin; 19-01-2013 at 10:50 AM.
To be fair, he only offers the possibility (as you rightly point out) along with other possible mechanisms -hence the reason I highlighted my word 'One'!
Thanks Gavin, I'm still with you and pleased that my mental image has been corrected.
Yes, perhaps it should be moved to Health. I'll be able to find it again easier when I study for Pests and Diseases that I plan to sit in March.
Kitta
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