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IPM 3 Fighting Varroa 3: Strategy – Understanding Varroa Population Dynamics




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What can we do to keep the mite population under control?

The first thing to keep in mind is that any mite control methods we use today are merely stopgap measures until the bees are genetically able to take over the battle for themselves (kind of like our “strategy” in Iraq). My feeling is that we need to rethink our paradigm, and switch from the strategy of blasting the mites with a chemical bomb after they’ve built up to dangerous levels, to a strategy of controlling mite buildup from the get go.

Those of you who keep asking for some new miracle control for the mite are ignoring the reality that we have at least two kinds of bees who are already demonstrating exactly how to do it! Apis cerana and the Africanized bees keep varroa in check unaided by us egotistical humans who think we need to solve everything ourselves! My guess is, that if we had focused our resources toward the development of resistant bees, rather than on chemical control, we wouldn’t be needing this discussion on mite control today.

The bees have already provided us a model of what works. Maybe we should attempt to emulate it. In essence, these bees use a brass knuckles approach every day to make life miserable for the mite. Our modeling of mite population dynamics confirms for us just why their strategies are successful. To wit:

Tactics used by mite-tolerant bees

1. Resistant bees are hell on phoretic mites, always grooming them off their bodies, harassing them, and increasing daily mite mortality. This action helps rid the colony of overwintering mites, and slows mite buildup in spring by keeping individual mites from breeding multiple times. We should seek out and breed from bees that exhibit strong grooming behavior (I think this should be a top priority). We can assist the bees with natural* chemical treatments during spring buildup, by using screened bottoms, and with an oxalic acid dribble in the fall.
2. Resistant bees rip out worker pupae if mites try to reproduce on them. This keeps baseline mite buildup in worker brood to a minimum. We can select for strong varroa sensitive hygiene.
3. Mite-infested drones of Apis cerana essentially sacrifice themselves by dying under the tough cell cap. Whole colonies abscond and leave mites behind. We should seek out and breed from bees whose infested drones die within the cocoon. We can help by minimizing the amount of drone comb, and by practicing drone brood removal during spring and summer.
4. Resistant bees never let mites build up to high enough levels to cause virus epidemics. We can monitor mite levels, and use natural chemical treatments if necessary in August to bring down mite levels.
5. Resistant bees produce fewer collapsing colonies to rob, and due to heavy grooming, are less likely to carry mites home. Ideally, we would isolate our apiaries. Realistically, we can minimize swarming by mite-susceptible colonies that will eventually collapse, we can prevent our own colonies from collapsing and spreading their mites, and we can monitor our colonies spring and fall to watch for sudden jumps in mite levels.
6. Resistant bees abscond frequently, and leave behind disease spores in the old combs. We can breed from bees that exhibit immunity to viruses. We can rotate out old combs that may be contaminated with chemicals, or harbor spores. We can also help suppress tracheal mite, nosema, and other diseases with good husbandry or medication.

* “Natural” chemicals such as oxalic or formic acid, thymol or essential oils, powdered sugar; as opposed to synthetics such as fluvalinate or coumaphos that leave harmful residues in the wax combs. I’m not touting “organic” beekeeping, just common sense methods based on good scientific research.

There you have it—a summary of the strategy and tactics that are successfully used by mite tolerant bees. These bees rarely allow varroa infestation to exceed the 2% level at any time of the year. We don’t have to reinvent the wheel! Mite tolerant bees are out there right now—let’s identify them and breed from them. In the interim, let’s follow their example, and help the rest of our colonies to survive and thrive!

A brass knuckles fighter doesn’t just bide his time, waiting for his one good shot with the “silver bullet”—instead, he sizes up his opponent and just keeps pounding away, never letting the opponent get the upper hand. The way we “pound” varroa is by an incremental approach. For example, if you plant a bed of lettuce in spring you know that you’re going to have to weed it to keep the weeds from shading the crop and stealing all the nutrients. The incremental approach would be to do a little hand weeding every week, and keep knocking the weeds back. The silver bullet approach would be to wait until the weeds grew tall, and then use your 50 horsepower garden tractor to mow ‘em down just before they smothered the lettuce. You’d save time, and still get a crop, but the lettuce would be small, stressed, and diseased. Varroa affects your bees the same way that weeds hurt your lettuce.

So let’s compare two strategies: brass knuckles vs. silver bullet. If you were to use the “brass knuckles” strategy—recruiting mite-fightin’ bees that can kill an extra 1% of the mite population each day (an additional 7% kill a week, or 35% a month), you’d retard the mite growth rate to less than 1½% a month. At that rate, 200 overwintered mites wouldn’t even reach a population of 2500 by the end of a full 6-month season of broodrearing! If you go a step further, and help the bees with biotechnical methods, or spring treatments, you’ll keep the upper hand on the mites. An incremental approach of hitting the mite with little jabs all through spring will win the fight. Mites only get out of hand because we ignore ‘em until they are in our face!

Compare this to the silver bullet strategy we’ve been using, letting them build up to 10 or 20 times their initial population over the course of a season, then gamble that your one good shot with the silver bullet in the fall will kill the 90-95% necessary for the colony to survive! Both approaches knock the mites back to the starting point, but the silver bullet approach results in a stressed colony being hammered by the mites for much of the season, which greatly decreases your honey crop, allows viruses to rampage, and greatly increases your stress level.

The only way we can tell if the bees (with our help) are successfully keeping the mite in check is by monitoring mite levels at appropriate times. In the next installment of this series, I’ll compare the various methods for monitoring mite levels, and make suggestions as to timing.

Acknowledgments

I want to be clear that I could not be writing this series of articles without the gracious help of many other beekeepers and researchers. Indeed, this series is a learning experience for me day by day, as I find new resources of information, printed or verbal. I’d especially like to thank Eric Mussen, Marion Ellis, Rob Currie, Marla Spivak, Gloria DeGrandi-Hoffman, Sue Cobey, Tom and Suki Glenn, Dewey Caron, Bob Harrison, Dave Cushman, Bill Truesdell, and Jerry Hayes. Newbie George Fergusson has been invaluable in helping me distill the information. I greatly appreciate the support and indulgence of editor Joe Graham, who lets me make last-minute revisions right up ‘til press time. For those of you that I forgot to mention, my apologies.

Resources for Information

ATTENTION RESEARCHERS:it would sure help us beekeepers if you would all have pdf links on your homepages to all your publications! Thank you to those of you who already do.

A great U.K. manual—“Managing Varroa” www.csl.gov.uk/science/organ/environ/bee/diseases/documents/managing_varroa_new.pdf
A great New Zealand manual—“Control of Varroa” http://www.biosecurity.govt.nz/files/pests-diseases/animals/varroa/control-of-varroa-guide.pdf

Population Modeling
The best summary of all the parameters: Martin, S. J. (1998) A population model of the ectoparasitic mite Varroa jacobsoni in honey bee (Apis mellifera) colonies. Ecological Modeling, 109: 267-281.
Martin, S. J. & Kemp (1997) Average number of reproductive cycles performed by the parasitic mite Varroa jacobsoni in Apis mellifera colonies. Journal of Apicultural Research, 36: 113-123.
Fries, I (200?) Dynamics of the parasitic (Varroa jacobsoni) population: Modeling criteria http://ressources.ciheam.org/om/pdf/c21/97605905.pdf

Fries, Camazine, Sneyd 1994 Population dynamics of Varroa jacobsoni: a model and review. Bee World 75: 5-28
DeGrandi-Hoffman, Gloria. & Robert Curry 2005 Simulated population dynamics of Varroa mites in honey bee colonies: Part II – What the VARROAPOP model reveals. Amer. Bee J. 145(8): 629-632.
Boot, Baalen, Sabelis 1995 Why do Varroa mites invade worker brood cells of the honey bee despite lower reproductive success? Behav Ecol Sociobiol 36:283-289.
D. Wilkinson and G. C. Smith 2002 A model of the mite parasite, Varroa destructor, on honeybees (Apis mellifera) to investigate parameters important to mite population growth. Ecological Modeling 148(3): 263-275.
VarroaPop download: http://gears.tucson.ars.ag.gov/soft/vpop/vpop.html
Literature Cited
Arechavaleta-Velasco, Guzman-Novoa. 2001. Relative effect of four characteristics that restrain the population growth of the mite Varroa destructor in honey bee) Apis mellifera) colonies. Apidologie 32: 157-174.
Aumeier, Pia. 2001 Bioassay for grooming effectiveness towards Varroa destructor mites in Africanized and Carniolan honey bees. Apidologie 32: 81-89.
Bieñkowska, Malgorzata & Zofia Konopacka 2001 Assessment of honeybee colonies infestation by the mite Varroa destruktor based on its natural mortality during the summer season. Journal of Apicultural Science 29(45)
Bieñkowska, Malgorzata & Zofia Konopacka 2001 Daily summer fall of Varroa destructor calculated from short (1,2,3, and 4-week) sampling periods to be used as an indicator of autumn mite infestation of honeybee colonies. Journal of Apicultural Science 143(45)
Currie & Gatien 2006 Timing acaricide treatments to prevent Varroa destructor from causing economic damage to honey bee colonies. Can. Entomol.138: 238-252.
Fries, Ingemar , Aasne Aarhus, Henrik Hansen and Seppo Korpela. 1991 Development of early infestations by the miteVarroa jacobsoni in honey-bee (Apis mellifera) colonies in cold climates. Exp. and App. Acarology 11(2-3): 205-214.
Harris, J.W., Harbo, J.R., Villa, J.D., Danka, R.G. 2003. Variable population growth of varroa destructor (mesostigmata: varroidae) in colonies of honey bees (hymenoptera: apidae) during a 10-year period. Environmental Entomology/Population Ecology 32(6):1305-1312.
Martin, S. J. & Medina, L. M. (2004) Africanized honeybees have unique tolerance to Varroa mites. Trends in Parasitology 20:112-114
Mondragon, Spivak, Vandame. 2005 A multifactorial study of the resistance of honeybees Apis mellifera to the mite Varroa destructor over one year in Mexico. Apidologie 36: 345-358.
Sumpter, D. J. T. & Martin, S. J. (2004) The dynamics of virus epidemics in Varroa-infested honey bee colonies. Journal of Animal Ecology 73:51-63 www.lasi.group.shef.ac.uk/pdf/Martin%2064.pdf

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