Are we looking in the wrong place?

[Neils]

I've been thinking about this for a while and I'm sure I must be getting it wrong but...

The emphasis is on looking for bees that can deal with varroa.

Should we not be looking for varroa that can deal with bees [without killing them]?

My reasoning is:

1) Varroa is a parasite. a parasite that kills its host normally fails (there are extenuating circumstances here so bear with me)

2) there are pockets of bees that "deal with varroa without treatment". They tend to be isolated and don't cope well when taken out of that isolated environment. why don't these supposedly tolerant bees cope when placed in a "general" population?

3) Granted the likes of Ron Hoskins might be working in the opposite direction, but he's still building up a "pocket" of tolerant bees, might he also be building up a pocket of tolerant varroa?

4) Varroa reproduce every 3 weeks (give or take) and produce 3+ offspring with a near 100% chance of success. Bees reproduce one or two times a year and might do 1-3 offspring with no better than 40% chance of success. If there's going to be an adaptation where is that more likely to take place? ( broad generalisation I know)

5) Varroa destructor and Jacobsoni are now apparently different enough that one can't survive on the other species of bee yet destructor kills Apis Mellifera while Jacobsoni can co-exist with Apis ceranae.

I'm painting broad brush strokes because I'd like to invoke discussion. Strike me down and you can educate with your wisdom ;)

My basic question remains, Should we be looking for tolerant Varroa rather than tolerant Bees?

[Easy beesy]

Hi nellie
Consider this-

Varroa doesn't kill bees. It simply weakens the immune system allowing something else (disease/virus/combination of factors) to kill bees. If you eradicate the other factors bees would probably co-exist with varroa.

[Jimbo]

I like your reasoning. If you think about it the varroa became quick enough to adapt to the varroacides that kill it. The easy route is though to kill the varroa as it would be more difficult to eradicate or have a quick tests for the many different virus vectors. Remember viruses can also adapt quickly. Just think of the common cold virus

[Jon]

If you eradicate the other factors bees would probably co-exist with varroa.

That seems to be true.


However, although colony collapse is associated with V. destructor, no direct link between the actual mite population and colony collapse has been found (Martin et al. 1998). Although eight collapsing colonies had estimated populations of between 2600 and 16 000 mites, seven surviving colonies had a similar sized mite populations (2500–15 000). This strongly suggests that other factors are also involved in the collapse of mite-infested colonies.

http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2664.2001.00662.x/full

This looks like an interesting study. Ten years old though.

Summary


1
The ecto-parasitic mite Varroa destructor is a serious world-wide pest of the honeybee Apis mellifera and has being linked with the death of millions of colonies, although its role in colony death has remained elusive.
2
A simulation model was developed to explain the link between the mite and collapse of the host bee colony, given that colony death does not always occur. We investigated the effects of two pathogens, deformed wing virus (DWV) and acute paralysis virus (APV), vectored by the mite, on the host colony.
3
Two previously published simulation models, a bee and a mite, were combined and adapted for use in temperate climates with a variety of bee diseases. The model was constructed using Modelmaker® software, which allows the progression of a disease in the host colony to be followed daily.
4
The population dynamics generated by the model were similar to those observed in a natural honeybee colony. When DWV- or APV-transmitting mites were introduced into the colony, its adult worker bee population collapsed either during winter or spring for DWV, or autumn to spring for APV. This corresponds well with field observations of colony death in Europe.
5
The model revealed that DWV initially had little effect on the colony but during late summer, as the population of DWV-transmitting mites increased, the virus caused a reduction in the number of healthy young bees entering the overwintering population. This imbalance in the age structure of the overwintering bees resulted in the eventual death of the colony during the winter or spring. As few as 2000–3600 mites in autumn could kill a colony.
6
In contrast, APV transmitted by Varroa was only able to kill the honeybee colony if a large (10 000+) mite population was already present when an overt APV infection occurred. It was difficult for APV to become established within the bee population due to it causing rapid host death.
7
The model predicts that the less virulent DWV will become more widely established than the highly virulent APV, and that mite control measures need to be taken prior to the production of overwintering bees.

[chris]

Varroa doesn't kill bees. It simply weakens the immune system allowing something else (disease/virus/combination of factors) to kill bees. If you eradicate the other factors bees would probably co-exist with varroa.

Jon posted this elsewhere on the forum.It appears to suggest that varroa alone can kill.

According to Moritz (1981), a
Varroa mite will consume 0.25 ml haemolymph
daily from its adult host, which suggests that the
vitellogenin consumption from a winter bee is
approximately 8 mg day1. This implies that the
lifespan of a worker in the winter season would
be reduced by 30% if it gets exposed to only a
single Varroa mite.

[Jon]

Hi Chris
-shortens the life span of the bee rather than killing it outright and that might still be compatible with coexistence.
The problem with mere coexistence is that the colony may not be of economic interest to anyone interested in producing honey if it is struggling to keep the numbers up due to bee living a shorter life.

There was an earlier thread on here which discussed why mites with a lower reproductive rate, ie less harmful to a bee colony, would be unlikely to dominate in a population in which faster reproducing mites were also present.

[Jon]

This paper (http://www.apidologie.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/apido/full_html/2010/03/m09176/m09176.html) gives good background info:

Varroa mites and honey bee health: can Varroa explain part of the colony losses?
Yves Le Conte1, Marion Ellis2 and Wolfgang Ritter3

[chris]

-shortens the life span of the bee rather than killing it outright and that might still be compatible with coexistence.
.

Hi Jon.Yes.In a sense. But to be pedantic, if you were going to live to be 100 and something shortened your life so you lived to just 70, then you could say that the something killed you.

Personally, I think one has to look at the system where bees tolerate varroa that tolerate bees that tolerate varroa that.............And they have to tolerate the beekeeper at the same time :p
I won't go any further or I might go down on the Bispham.

[Jon]

I don't have the reference at hand but is there not evidence that bees are becoming somewhat better at coping with varroa as compared to several decades ago when the mites first made the species jump. There is bound to be some selection pressure favouring bees which cope better, even when a lot of colonies are having mite numbers reduced by the various varroa treatments. Mike B thinks that resistance can never arise when the majority of colonies are being treated but I have to say I do not agree with that. Bees which cope better with varroa are more likely to survive, produce drones, swarm and generally increase their percentage of genes in the gene pool irrespective of treatments being applied. I suppose the argument could be about the speed of the development of resistance but most beekeepers want to avoid massive colony loss. When a population is drastically reduced in a short period of time it can lead to a genetic bottleneck. Beekeepers can breed from healthy stocks which also show signs of coping with varroa to some extent.

And to try and answer Neil's point number 2. in the initial post, there are different haplotypes of varroa with varying degrees of virulence. A good reason why we should think carefully about honeybee imports. Varroa first appeared in Ireland in Sligo and was (allegedly) brought in on several full colonies driven over from England in the back of a van. The last thing we need is a second wave of a more virulent strain.


V. destructor genetic variability could explain differential colony losses if different haplotypes or strains of mites have different degrees of virulence to the bees, leading to differences in host-parasite equilibrium. It has been shown that two major mite haplotypes have spread over the world, the Japanese and the Korean haplotypes (Anderson, 2000), which might have different virulence depending on the haplotype (Correa-Marques et al., 2003; Vandame and Palacio, 2010). Each haplotype has a clonal genetic structure (Solignac et al., 2005). While it is unlikely that different Varroa haplotypes could explain the recent colony losses, two new haplotypes of Varroa destructor were recently described in A. mellifera colonies in Southeast Asia (Navajas et al., 2009). Nothing is known about their virulence on European bees outside Asia, but those haplotypes might be a new threat to consider for A. mellifera bees outside Asia. Importation of bees from Asia should be considered carefully, since the impact of introducing Asian haplotypes to A. mellifera populations outside of Asia is unknown. The recent discovery of the Japanese haplotype in Spain makes it evident that HB market exchanges can disperse pathogens and parasites (Munoz et al., 2008).

[chris]

I don't have the reference at hand but is there not evidence that bees are becoming somewhat better at coping with varroa as compared to several decades ago when the mites first made the species jump.

Could it be this?
Apidologie 38 (2007) 566–572 Available online at:
c INRA, EDP Sciences, 2007 www.apidologie.org
DOI: 10.1051/apido:2007040
Original article
Honey bee colonies that have survived Varroa destructor*
Yves Le Contea, Gérard de Vaublanca, Didier Crausera, François Jeanneb,
Jean-Claude Roussellec, Jean-Marc B´ecarda

To come back to the original question,I'll try to keep this simple because much is beyond my understanding.Please correct any flaws in my reasoning. If we find a mite that deals with bees, what does this mean? That the varroa doesn't kill the bee colony or overweaken it. How can this happen? By the mite reproducing less rapidly. If this varroa were present along with one that reproduces more rapidly, would it survive? Basically what I'm wondering is could more virulent and less virulent mites coexist or will the more bee friendly ones be doomed?

[EmsE]

Thinking about Neil's 4th point, it would seem that Varroa could evolve quicker due to the reproductive cycle, however as they are interbred, wouldn't this would significantly reduce their ability to do so? Is their ability to become resistant to certain treatments something they develop, just like humans becoming less susceptible to the cold (albeit something that they can pass through the generations) or is it genuinely a genetic adaptation.