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Varroa-Virus Interaction in Collapsing Honey Bee Colonies

Discussion in 'Disease & Pests' started by Dave Black, Mar 20, 2013.

  1. Dave Black

    Dave Black Guard Bee Donor 2014 Donor 2013

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    A small but timely study published today. The comments regarding autumn (as usual transpose the months for the southern hemisphere) are interesting. Just sneaks in below the 1Mb limit. :)

    Abstract.
    Varroa mites and viruses are the currently the high-profile suspects in collapsing bee colonies. Therefore, seasonal variation in varroa load and viruses (Acute-Kashmir-Israeli complex (AKI) and Deformed Wing Virus (DWV)) were monitored in a year-long study. We investigated the viral titres in honey bees and varroa mites from 23 colonies (15 apiaries) under three treatment conditions: Organic acids (11 colonies), pyrethroid (9 colonies) and untreated (3 colonies). Approximately 200 bees were sampled every month from April 2011 to October 2011, and April 2012. The 200 bees were split to 10 subsamples of 20 bees and analysed separately, which allows us to determine the prevalence of virus-infected bees. The treatment efficacy was often low for both treatments. In colonies where varroa treatment reduced the mite load, colonies overwintered successfully, allowing the mites and viruses to be carried over with the bees into the next season. In general, AKI and DWV titres did not show any notable response to the treatment and steadily increased over the season from April to October. In the untreated control group, titres increased most dramatically. Viral copies were correlated to number of varroa mites. Most colonies that collapsed over the winter had significantly higher AKI and DWV titres in October compared to survivors. Only treated colonies survived the winter. We discuss our results in relation to the varroa-virus model developed by Stephen Martin.

    Francis RM, Nielsen SL, Kryger P (2013) Varroa-Virus Interaction in Collapsing Honey Bee Colonies. PLoS ONE 8(3): e57540. doi:10.1371/journal.pone.0057540

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  2. frazzledfozzle

    frazzledfozzle Guard Bee Donor 2014 Donor 2013

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    Very interesting article Dave thanks for that :)
  3. tom sayn

    tom sayn Guard Bee Donor 2014

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    23 colonies on 15 apiaries, that makes about 1,5 hives per apiary?
    they surely must have ccd in the usa.
  4. frazzledfozzle

    frazzledfozzle Guard Bee Donor 2014 Donor 2013

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    A couple of questions come to mind.

    Do they have any resistance to flumethrin where ever this study took place ( Denmark?)

    If they do would that explain the high levels of DWV in bees even after treatment?

    Are there any visual signs of a colony having DWV apart from the actual deformed wings of severely affected bees?

    Can you have a high number of bees in a colony carrying the DWV with no outward symptoms?
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  5. JohnF

    JohnF Pupa

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    We are using the same AKI assay in our lab (and a different assay for DWV). We have seen low levels of DWV in many samples (10 bees rather than 20 bees used in the paper) from hives with no outward symptoms . .and v. low level varroa (including my own hive . . 2-3 mites per 300 bees by sugar shake . . done several times over 2 weeks last month). Treatment went in last week but warranted based on the numbers? The detection of Deformed Wing spurred me more I think !

    We haven't detected much of the AKI complex to date.
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  6. deejaycee

    deejaycee Guard Bee Donor 2013

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    hehe.... I was just reading this paper over lunch and thinking to myself as I went through the methodology "bloody hell.. I need JohnF here to translate this. For all I know they could be using alternate names for snake oil and divining rods!"
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  7. frazzledfozzle

    frazzledfozzle Guard Bee Donor 2014 Donor 2013

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    Once a colony has DWV how can it be got rid of? Is it something that keeps multiplying both in the bees individually and in the number of bees infected in the colony?

    How is the virus transmitted? I know it's spread thru varroa, can it be spread by the bees as well?

    Once it's found in a colony can it be completely removed somehow or is it likely that in time it will be in all colonies throughout NZ, if it's not already?
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  8. deejaycee

    deejaycee Guard Bee Donor 2013

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    If I recall correctly, DWV was believed to be in our NZ population pre-varroa, but very, very rarely seen, and not a noteworthy problem when it was.

    Assuming that's correct, I believe its rarity and low effect would have been because it's primarily a blood (haemolymph)-borne disease and as a result of the lack of a vector - varroa.

    Something like malaria with no mosquito to trasmit it.
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  9. frazzledfozzle

    frazzledfozzle Guard Bee Donor 2014 Donor 2013

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    Thanks Dee that explains it for me :)
  10. Dave Black

    Dave Black Guard Bee Donor 2014 Donor 2013

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    The first survey of viruses in NZ was by Dennis Anderson in 1988 and DWV wasn't found. The next was Brenda Ball's, with New Zealand's Jacqui Todd, in a study published several times over the next five years. It was conducted with samples collected in 2001-2002, just after varroa arrived. No DWV. The next bit of work was done with samples collected in 2003, although the paper wasn't published until April 2007. (Hermann Pechhacker, who was at the Waikato Field Day recently was a co-author of the paper). No DWV. In March 2007 Biosecurity NZ anounced the first 'find' of DWV in Northland and Waikato.

    Before varroa, DWV was never a problem. The only obvious symptoms are the deformed wings (obvious if you don't have acarine), but it decreases life-span, can cause odd body colouring, and shorter abdomens, not that you can tell. As it has been detected in and replicates in larvae, pupae, adults, drones (especially drone semen) and queens we know it has several modes of transmission, both horizontal (bee to bee) and vertical (queen to worker). We also know that not only is it vectored by varroa, it replicates in varroa. As far as I know it does not cause the death of larvae, seldom causes the death of pupae, and rarely causes the death of an adult. It does not, by itself, induce cell death or lysis. It may interfere with vitellogenin synthesis.

    I have heard speculation that is was introduced with drone semen imports, the first of which occured in 2004. That is certainly possible, but I can see no reason why it did not arrive with varroa in 2000. To my mind, especially given Stephen Martin's work in Hawai'i, it is more clearly associated with and spread by varroa, but the fact is that it was not detected until after the semen imports. However, the studies may have been too early and too small to discover it before then.

    In the absence of a vector like varroa the titre of DWV should diminish with time, but it would never completely go away as it does not depend on varroa for its transmission. It can be low enough though so that it isn't a problem, and could become a latent infection (dormant, non-replicating particle) unless something (like varroa) were to activate it again. In contrast, KBV would disappear in such circumstances because it kills its host in pretty short order, and that prevents the host from spreading it around. There has been work done that suggests the DWV infection does indeed diminish if you kill off varroa. Different 'strategies' used by the various viruses profoundly affect the dynamic of a varroa infection, and that's why I think is important to know which virus you are trying to 'manage'.

    I don't know as a fact if resistance has been shown in Denmark, but I'd bet money on it. It doesn't really matter. Really though the thing about DWV is that is all about the timing. If your treatment was to kill all the mites, but after they had vectored DWV to every bee in the colony, it would be too late - no varroa but dead colony. On the other hand, with very low DWV titres you could have lots of varroa and the colony survives, at first. The paradox is that DWV is spread so easily you must keep the mite population really low to limit it, whereas KBV, which doesn't spread so easily, can permit higher mite loads before things get out of hand. The progress/pattern of disease of varroa infestations in the North Island suggests to me that DWV gradually suplanted KBV as the associated virus killing colonies. KBV has always been here, DWV is recent.

    This varroa business is so simple I don't know why we haven't licked it before now! ;)
  11. frazzledfozzle

    frazzledfozzle Guard Bee Donor 2014 Donor 2013

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    Dave in your opinion do you think there's ever likely to be a break through in managing varroa effectively either through a fool proof treatment or maybe genetic manipulation of varroa itself?
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  12. tom sayn

    tom sayn Guard Bee Donor 2014

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    i'm seriously frustrated on that matter, too. since 25 years now i hear these stories about the big scientific breakthrough and this or that resistant bee and now i find myself back to formic acid where i started 25 years ago.
    25 years ago varroa was less a problem than it is now.
    hard to not turn cynic sometimes.
    but i believe there is great potential in the internet and forums.
    possibly a new way to work with breeders, scientists, large and small commercials and hobbyists in a totally new cooperative way.
  13. frazzledfozzle

    frazzledfozzle Guard Bee Donor 2014 Donor 2013

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    To be honest I think If countries like the USA where they have many more beekeepers, scientists and money than we do still have no answer to varroa I seriously doubt that anything we do down here will make a blind bit of difference :(
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  14. JohnF

    JohnF Pupa

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    earlier studies were using less-sensitive ELISA methods - or in the case of the 2007 paper and DNA methods, a very small sample size (5 bees or so?) . . .of course if it was here at all Dave, as you say

    I am detecting DWV at very low level in my own hive (with very low varroa levels I think - but then I *am* a newbie) and will look at this again in future. Agreed, there is little chance of removing it completely it appears (requeening has been suggested for some viruses?). However, a paper a while back showed DWV level actually rose with some varroa treatments, suggesting the treatment made the bees more susceptible to infection (DWV levels then decreased over time).

    I would be interested in looking at the genetic variation of DWV over time, as per the Hawaian work, along with the viral load to see if DWV is indeed becoming more virulent - and targeted. And yes, based on the Todd paper and virus prevalence, I would have expected to see more KBV.[/quote]
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  15. Shaun

    Shaun Guard Bee Donor 2014 Donor 2013

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    You forget the Ingenuity of the "number 8 wire kiwi". I feel that it is quite possible that here in NZ we will find a way to manage varroa if not entirely over come it.
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  16. tom sayn

    tom sayn Guard Bee Donor 2014

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    if you look at the numbers most of these breeding programs are based on, you really can't expect much progress.
    actually they still struggle to even identify tolerance, let alone selecting for it. varroa tolerance has been a history of error.
    maybe we can find a easier, better way to select for it in a program that involves 10.000 hives.
  17. JohnF

    JohnF Pupa

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    Rather glibly, "anything is possible, the impossible just takes a little longer"

    NZ scientists punch well above their weight - I think overseas people will go 'so and so will be working on that because they're the expert and so we'll leave it to them' while so-and-so is actually working on something else.
    Some encouragement:
    - People in Italy working on Psa in kiwifruit since 2008. Call on NZ scientists to help
    - just recently, NZ scientists (in Otto's dept) trace the origins of Psa-V to China using latest sequencing technologies
    - potatoes wrecked by a psyllid in the USA since 1994 or so. Is it transmitting something? Once symptoms were found NZ, NZ scientists found the agent in 6 months (Liberibacter - a virus-like organism). The team was headed by an MPI scientist (and ironically, the head of that group developed many of the DNA assays for bee viruses currently used in the UK)

    Stepping down off soapbox now - hope that's some encouragement that if someone's gonna do it, it might as well be us :)
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  18. tom sayn

    tom sayn Guard Bee Donor 2014

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    very interesting, John. do you still find that paper?
    What do you think about the theory that neonics make the bees more susceptible to viruses?
    aren't some neonics "designed" to do exactly that?
    lately we hear phrases like "we need to control viruses instead of focusing on killing varroa mites."
    but those who suggest that haven't come up with any clues how to reduce viruses apart from killing varroa.
    do you think there could be other ways to lower the virus load?
  19. tom sayn

    tom sayn Guard Bee Donor 2014

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    very interesting theory. i think you are right there.
    ten years back the "psm picture" looked very different from now.
    now a hive with a relatively low varroa load gets taken out by dwv and doesn't get much of a chance to develop any other problems.
  20. JohnF

    JohnF Pupa

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    Hunting through files, the paper I was referring to Tom is from 2011:
    Acaricide Treatment Affects Viral Dynamics in Varroa destructor- Infested Honey Bee Colonies via both Host Physiology and Mite Control
    Abstract
    Honey bee (Apis mellifera) colonies are declining, and a number of stressors have been identified that affect, alone or in combination, the health of honey bees. The ectoparasitic mite Varroa destructor, honey bee viruses that are often closely associated with the mite, and pesticides used to control the mite population form a complex system of stressors that may affect honey bee health in different ways. During an acaricide treatment using Apistan (plastic strips coated with tau-fluvalinate), we analyzed the infection dynamics of deformed wing virus (DWV), sacbrood virus (SBV), and black queen cell virus (BQCV) in adult bees, miteinfested pupae, their associated Varroa mites, and uninfested pupae, comparing these to similar samples from untreated control colonies. Titers of DWV increased initially with the onset of the acaricide application and then slightly decreased progressively coinciding with the removal of the Varroa mite infestation. This initial increase in DWV titers suggests a physiological effect of tau-fluvalinate on the host’s susceptibility to viral infection. DWV titers in adult bees and uninfested pupae remained higher in treated colonies than in untreated colonies. The titers of SBV and BQCV did not show any direct relationship with mite infestation and showed a variety of possible effects of the acaricide treatment. The results indicate that other factors besides Varroa mite infestation may be important to the development and maintenance of damaging DWV titers in colonies. Possible biochemical explanations for the observed synergistic effects between tau-fluvalinate and virus infections are discussed.

    Yes, I think there are a number of factors making bees more susceptible (apart from increased virulence seen in some viruses). One might imagine that control of viruses exceeding defined thresholds in the future might be along the lines of AFB (with the exception of burning the actual hive) - depends on how seriously the issue is taken
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