Varroa Doubling Info: Understanding the BOOM
and Assessing your Varroa Treatment “time purchase”

David VanderDussen,
NOD Apiary Products, January 23, 2006
PO Box 117, Frankford, ON, Canada.

Beekeepers have often been surprised at rapid increases in varroa levels. Colonies that were showing few mites several weeks earlier suddenly seem to have high varroa loads. Varroa don’t appear out of nowhere. What is the explanation?

The answer can be found in a math riddle: if a jar has bugs in it that are reproducing so fast that they double in number every minute, becomes full at 30 minutes, when was the jar half full? The answer, of course, is 29 minutes, one quarter full at 28 minutes, one eighth full at 27, etc. So the question becomes: how long is a varroa reproduction “minute”, and what is the varroa “jar”?

With varroa, the "jar" is the mite load the bees can function with, identified as 2,500 varroa for Great Britain and approximately 3,200 in the US ¹. This is because varrroa control should be approached as a brood disease². The post capping period is 12 days for worker brood³.  If a queen is laying 1,000 viable worker eggs a day, 12,000 developing larvae are under the cap.  If there are 3,000 varroa in a colony, one quarter of the brood is at risk. Three weeks later, half the brood in the colony is at risk. Colony collapse is fast approaching, putting it as a major source of infestation for surviving colonies in the area.

Varroa Reproduction Timeline when brood is present, unselected stock.Varroa reproduction: Each foundress mite starts out with 25-30 eggs⁴, consuming 5 - 6 per reproductive cycle⁵. In worker brood varroa spends 12 days under the cap, 4-6 days phoretic⁶. One foundress mite produces one viable female offspring per reproductive cycle, doubling the varroa load. In drone brood there is 14 days under the cap, 4-6 days phoretic, and 1 foundress varroa produces 2.2 viable female offspring per reproductive cycle, increasing varroa load by 3.2 times⁷.

Result: Due to compounding, by the end of 16 weeks each foundress mite will be responsible for approximately 32 viable female offspring. The varroa “minute” works out to 22.4 days (figure 1), approximately 3 weeks.

unselected stock chart: 16 weeks is 112 days with 5 doubling periods the varroa double every 22.4 days # varroa doubling period (22.4 days) day 100 0 0 200 1 22.4 400 2 44.8 800 3 67.2 1600 4 89.6 3200 5 112

Figure 1

Buying time:

Since eradication of the varroa mite is considered impossible⁸, when beekeepers use a control product what they are doing is buying time between treatments. The efficacy of the product determines how much time a treatment will buy (figure 2). 

Efficacy of Treatment Time Bought Chart starting varroa load: 3000 mites working with unselected stock   treatment % efficacy time bought (weeks) # of varroa remaining 99.9 30 3 99.8 27 6 99.61 24 12 99.22 21 23 98.44 18 47 96.88 15 94 93.75 12 188 87.5 9 375 75 6 750 50 3 1500 0 0 3000   -3 6000   -6.00 doomed

Figure 2

At the 3000 mite treatment threshold, if a treatment has a 97% efficacy, 3.75 months has been bought between treatments. At an 87% efficacy, 2.25 months.

Hard chemicals (fluvalinate – Apistan®, coumaphos – CheckMite+™), which have historically offered close to 100% control, are failing ⁹. Beekeepers are being forced to adopt other management strategies which may include long term soft chemical options. Currently available options in the US include Sucrocide™, Mite AwayII™ Single Application Formic Acid Pad, ApiLife Var®, and Apiguard™. 

Exercise:

Here are examples of several varroa treatment products, as assessed by Stanghellini and Raybold for varroa treatment in the fall of 2003, in New Jersey, USA ¹⁰:
single deep colonies:
Apistan®: 97%, Sucrocide™: 96%, oxalic acid 92%, ApiLife Var®: 91%, and MiteGone™: 79%
double deep colonies:
Apistan®: 95%, Sucrocide™: n/a, oxalic acid 93%, ApiLife Var®: 69%, and MiteGone™: 66%

Put these results on the chart above and see how much time you are buying.

Take home message: pay attention to the efficacy of the products you’re using. 1) Is what you are using working?, 2) are you buying the time you need to prevent major colony losses? and 3) skipping a treatment may mean loss of that treatment window and colonies going over thresholds before the next window.

Varroa Treatment Regimen Models:

For commercial beekeepers doing migratory beekeeping an IPM program is difficult to establish. The colony movement alone, with constantly shifting environments and locations, makes monitoring and following through on varying treatment requirements difficult. Most operations run crews to do the work and look for routines by which to function. Even non-migratory beekeepers may not be able to follow through on an IPM program due to the assessment skills required ¹¹.

A proven treatment regimen suitable for North Eastern USA is outlined in the Cornell University Master Beekeeper Program, using the Mite AwayII™ Single Application Formic Acid Pad (MAII), where two treatments are applied, one in the spring and one early fall ¹². 

NOD Apiary Products, the developer of the MAII pad, outlines a treatment regimen of two treatments per year for Canada and the Northern US, one in the spring and one early fall ¹³. The MAII formulation provides a 93.5%±5% control ¹⁴, and has been shown to provide adequate control as a stand alone varroa control product for four years in Canada ^15,16

The Southern States and migratory beekeeping may require a different regime. MAII applied three times per year for the three point migratory route of 1) going to California for pollination to 2) a Southern State for colony buildup and to 3) a Northern State for honey production ¹⁷, should provide good control. For colonies that stay in the South and experience high temperatures for much of the year a treatment program including the use of Apiguard™ (efficacy 90-93% ¹⁸) may be required.

The value of breeding programs

Attempts are being made to produce lines of bees that are capable of coping with varroa and tracheal mites. Initially the goal was to find or develop a “resistant” stock. Most researchers are now using the term “tolerant” stock and are working on stocks that will have the capability to survive longer between chemical treatments ¹⁹.

For a comparison to the standard unselected stock let’s look at the Russian Bee Importation program goal. The original goal was to increase the time for varroa load to go from 100 varroa to 3,000 varroa from 16 weeks to 30 weeks, when brood is present ²⁰. 30 weeks is 210 days with 5 doubling periods (the “varroa minute” in our “jar” model), so the mites double every 42 days (figures 3 and 4).

Goal Chart   Russian Unselected # varroa doubling period days to double days to double 94 0 (start) 0 0 188 1 42 22.4 375 2 84 44.8 750 3 126 67.2 1500 4 168 89.6 3000 5 210 112

Figure 3

Figure 4
(click on chart to see full size image)

With the Russian project goal, the beekeeper would have approximately 7 months between treatments if a treatment has a 97% efficacy, 4.25 months with 87% efficacy, when brood is present. 

With varroa, our "doubling minute" is approximately 3 weeks with unselected stock, but this can be extended with selected stock, potentially reducing the number of treatments required.

1. Mites of the Honey Bee, various authors, edited by Webster, T.C., and Delaplane, K.S. © Dadant & Sons Inc. 2001, 51 south 2nd St., Hamilton, Illinois, USA, page 234
2. ibid, page 143
3. ibid, page 140
4. ibid, page 143
5. ibid, page 140
6. ibid, page 135
7. ibid, page 144
8. ibid, page 229
9. ibid, page 241
10. American Bee Journal, June 2004, Vol. 144. No.6
11. Mites of the Honey Bee, various authors, edited by Webster, T.C., and Delaplane, K.S. © Dadant & Sons Inc. 2001, 51 south 2nd St., Hamilton, Illinois, USA, page 232
12. Integrated Pest Management Varroa destructor in the Northeaster United States Using Drone Brood Removal and Formic Acid. The Bee Files, Cornell University, © Nicholas W. Calderone, Department of Entomology
13. NOD Apiary Products press release announcing Mite AwayII™ receiving US-EPA Section 3 pesticide registration. April 2005.
14. Skinner, A., Tam, J., Ross, S. OBA TTP report for 2003, The Sting, Vol 21 no.4. Published by the Ontario Beekeepers Association.
15. VanderDussen, D., 2006, River Valley Apiaries, Stirling, ON Canada, Testimonials for Mite Away Single Application Formic Acid Pads
16. McRory, Doug, Ontario Provincial Apiarist, Planning Treatments for the Fall, The Sting, August 2005. Published by the Ontario Beekeepers Association.
17. VanderDussen, D, presentation to the American Honey Producers Association, January 14, 2006. Synopsis submitted for publication to The Honey Producer.
18. Apiguard™ promotional handout materials, Vita (Europe) Ltd., 21/23 Wote Street, Bassingstoke, Hunts, RG21 7NE, UK.
19. Mites of the Honey Bee, various authors, edited by Webster, T.C., and Delaplane, K.S. © Dadant & Sons Inc. 2001, 51 south 2nd St., Hamilton, Illinois, USA, page 205
20. Harris, J.W., presentation at the Ontario Beekeepers Association Commercial meeting, Milton, ON, August 2003

New Product

Introducing our latest product launch:
The Bee Brief... more

Latest News