TO SHOW THAT VARROA DESTRUCTOR PREFERS

AND HAS BETTER BREEDING SUCCESS ON LARGE CELL SIZE WORKER BROOD

COMPARED TO SMALL CELL SIZED WORKER BROOD OF APIS MELLIFERA MELLIFERA

��Dr Robert D Borrill

��Beekeeper

First published in Bee Craft Jan 2007 (BBKA) "Cell Size & Varroa Borrill, R, D.

Summary

A comparison of the behaviour of Varroa destructor (Varroa) on large cell worker brood (5.0mm � 5.8mm) and small cell worker brood (4.9mm) using mite falls and fecundity percentage as indicators.

Reference is made to honey bees, which naturally cope with Varroa.

Introduction

Varroa destructor (Varroa) has been in the British honeybee population for a number of years.� It threatens all parts of apiculture in this country, from backyard beekeepers to large commercial producers.� The potential effects of this mite go beyond beekeeping; the adverse economic implications are potentially huge¹for all aspects of agriculture and horticulture that depend on bees for pollination.� Although there are effective chemical treatments for Varroa, there have been reports of the mites developing resistance,^2�which render these treatments less effective.� There is also a concern that chemical treatments may leave residues in the honey, and may affect claims to "organic" status.

Non-chemical approaches to the control of Varroa in the honeybee are attractive.� In�the USA Dee and Ed Lusby³ have reported that decreased foundation cell size reduced Varroa infestation.� The Lusbys started to use 4.9mm cell size foundation in 1997 (800 colonies), and now run their entire commercial operation with it:� They�claim never to use chemicals for mite control.

By September 2002 I had in my apiary, both large (5.0mm � 5.8mm) and small (4.9mm) worker cell⁴ colonies of A mellifera, giving me the opportunity to count and compare the mite falls from both large and small cell worker brood during the usual autumn Apistan treatment for Varroa.

The result was surprising � the small cell mite fall was at least three times greater than the large cell mite fall.

Results - September 2002

Large cell average total mite fall [1 fall after 2 days] � 125 (100-250)⁵ n = 6

Small cell average total mite fall [1 fall after 2 days] � 438 (370-500) n = 8

September 2003� �� Repeat of Test Carried Out September 2002
�� (4 Falls at 2 Day Intervals)
Apistan
Large Cells
(Hive Total and Range)
Counted over 8 days
�
Apistan
Small Cells
(Hive Total and Range)
Counted over 8 days
87 (1-53)
269 (3-210)
109 (1-74)
178 (3-113)
176 (2-115)
562 (15-430)
233 (11-166)
394 (15-229)
146 (3-113)
640 (54-399)
�
282 (8-211)
Apiary Average Total
Large 150(n = 5)
Small 387 (n = 6)

These are similar results to the 2002 results but as there was no prior equalisation of mite numbers per colony, the results of both tests were open to the criticism that the high small cell mite count was the result of a higher infestation of the small cell colonies in the first place.

September 2004

Decided to over winter the small cell colonies untreated but the large cell colonies were treated with Apistan in the usual way.� The following April 2005 record was made of over wintering success and spring mite falls counts from Apistan administered in April 2005 to both large and small cell hives.

Results - April 2005

Results April 2005�� Both groups over wintered without loss.
Apistan October 2004
Large Cells
(Hive Total and Range)
Counted over 10 days
�
No Apistan October 2004
Small Cells
(Hive Total and Range)
Counted over 10 days
21 (1-8)
71 (1-49)
58 (2-31)
246 (5-193)
61 (2-51)
183 (1-139)
39 (3-25)
918 (25-275)
22 (1-8)
222 (4-92)
13 (1-4)
671 (69-244)
20 (0-7)
947 (44-313)
15 (1-5)
35 (1-15)
24 (1-6)
�
Apiary Average Total
Large 30 (n = 9)
Small 411 (n = 8)

As a result of Apistan treatment in April 2005 the initial mite populations of the colonies used in the September 2005 test should be fairly even.

Results September 2005��
Apistan Large Cells
(Hive Total and Range)
Counted over 30 days
�
Apistan Small Cells
(Hive Total and Range)
Counted over 30 days
576 (3-127)
758 (3-284)
217 (2-74)
240 (2-56)
223 (1-98)
302 (4-114)
Apiary Average Total
Large 338 (n = 3)
Small 433 (n = 3)

Summary of Results

DATE
SMALL CELLS
LARGE CELLS
September 2002
438 (n = 3)
125 (n = 6)
September 2003
387 (n = 6)
150 (n = 5)
October 2004
No records
No records
April 2005
411 (n = 8)
30 (n = 9)
September 2005
433 (n = 3)
339 (n = 3)

Discussion

The purpose of this paper is to explain the consistently higher mite fall on the small cell worker comb, which was repeated over four consecutive years.� It is well documented that Varroa choose to reproduce on the large celled drone brood � ten to twelve fold more frequently than on the smaller cell worker brood⁶.� The evidence gathered in the tests recorded here supports the hypothesis that a similar � if reduced � preference of Varroa to use large cell worker brood, rather than the small cell worker brood:

(i)�� By examining individual cells

�
Cells Examined
No. with Mites
No. of Mite Offspring
�
Fecundity %
Drone
87
11
Not recorded
�
12.6%
Large Worker
614
27
25
1 Daughter/ 24 Cells
4.3%
Small Worker
718
21
22
1 Daughter/ 32 Cells
2.9%

(ii)�� By colony mite falls

If we consider the mite fall evidence � smaller mite fall on larger cells could be explained by a greater percentage of mites accepting the large cells to breed in.� According to Buchler,⁷ up to 85% of the Varroa present in a colony may shelter in sealed brood during the breeding season and are therefore sheltered from miticide treatment � thus with less mites exposed to Apitsan fewer mites will fall to be counted.

If we look at those bees which naturally seem to be able to cope with Varroa and compare with A. mellifera.

Bee Type
Worker Cell Size
Relative Reproduction Rate on Worker Brood
Number of Weeks When Breeding Possible (Worker or Drone)
Grooming and Hygenic Behaviour
Africanised⁸
4.5 - 5.0⁹
Lower than A. mellifera¹⁰
Worker � 42 weeks¹¹
Strong
Apis cerana
4.7 � 4.9
No reproduction¹²
Drone Only � 2 cycles of about 10 weeks per year¹³
Strong
A mellifera "Natural" 1890
4.72 � 5.3¹⁴
-
-
-
A mellifera "Bought" Foundation
5.0 � 5.8¹⁵
Mites do better in larger cells
Worker � 42 weeks
Drone about 20 weeks
Weak � but improvement possible

Small cell worker brood is a feature of both A cerana and Africanised European bee, which manages to coexist with Varroa.� Both these bees are competent at killing mites during grooming.� A. mellifera has no really effective grooming, but improvement by selective breeding appears to be possible¹⁶.� Note also that in A. mellifera mellifera colonies Varroa can breed for 42 weeks on worker brood compared to A cerana's 20 weeks per year on drone brood.

Conclusion

Despite limited facilities, which in turn means less recorded data than ideal, the available results strongly suggest that when a beekeeper uses foundation with a worker cell size larger than 4.9mm on native British bees, he is unintentionally assisting the Varroa to thrive and consequently undermining the well being of his colonies.� Small cell foundation when used in conjunction with sugar powder¹⁷ gives an effective chemical free control of Varroa.

References

1.�� LEVIN (1983).� Value of crops depending on pollination amounts to �� US$19,000 million (1983 value), which is 143 times the value of honey �� and wax produced.

2.�� Mite resistance to pyrethroids (Managing Varroa � DEFRA 2005 page 24).� Spring 2005 � Resistant mites well established in southwest UK.� Pockets of resistant mites confirmed in other parts of England and Wales.

3.�� LUSBY, D & E.� Pioneers in the use of small cell foundation.� (Osterlund A BJ 141/8)

4.�� Cell size.� Measured across parallel sides in millimetres.� As A cerana and A.m scutellata have a better developed natural resistance to Varroa and because the upper size limit of worker brood cells in both is 4.9mm, cells larger than 4.9mm are referred to as large (5.0mm � 5.8mm) and cells 4.8mm � 4.9mm are referred to as small if this paper.

5.�� The mite count in 2002 was by estimation to the nearest 100 mites � not accurate enough for the later work.

6.�� Managing Varroa.� (DEFRA page 3).

7.�� BUCHLER, R (1997).� Lecture Kirkley Hall Newcastle.

8.�� Africanised European Bee.� A cross between the European honeybee (A. mellifera) and A. mellifera scutellata � a vigorous bee brought to th Americas to enhance honey yield.� Noted for its aggressive behaviour,� with effective grooming against Varroa.� Africanised bees also inherited effective grooming ability of A. mellifera scutellata¹⁰.� Note:� Arizona where Dee and Ed Lusby keep bees is now Africanised and this may well contribute to the Lusbys' success with 4.9mm cell size foundation.

9.�� Worker cell sizes of different bee races.� (CRANE, E � Bees and Beekeeping page 135).

10.�� Varroa reproduction rate on Africanised bees is less than the reproduction rate on A. mellifera worker brood (Medina and Martin 1142/04 Africanised honey bees have unique tolerance to Varroa mites).

11.�� MEDINA, MARTIN, ESPINOSA MONTANO, RATNIEKS (2003) � (Reproduction of Varroa Destructor in worker brood of Africanised honey bee).

12.�� Varroa does not reproduce on A cerana worker brood only on drone cells.� (D L ANDERSON AND SUKARSIH (1996) � Changed Varroa jacobsoni reproduction).

13.�� RATH, HW (1991).� (Investigations on the parasitic mite Varroa jacobsoni).� Described cycles of brood rearing in A cerana as "59.5 (<+->33.4) days alternating with periods of 55 <minus>134 days when no drone brood was present.

14.�� A. mellifera "natural" my name given to the native British bee described in 1890 by Cowan (Honey Bee, its natural history, anatomy and physiology page 181).� This before foundation was as common as it is today.� He describes "natural" worker cell size as .0186" - .0211" (4.72mm � 5.3mm)

15.�� A. mellifera "bought foundation" my name for A. mellifera mellifera that has been reared on bought foundation.� Size range 5.0 mm � 5.8mm.

16.�� THALER, M (ABJ144/10) describes a safe way of detecting Varroa resistant colonies with a view to enhancing Varroa resistance by selective breeding.

17.�� FAKHIMZADEH, K (2000).� Potential of super-fine ground, plain white sugar dusting as an ecological tool for the control of Varroasis in� A. mellifera.

18.�� FAKHIMZADEH, K.� The effects of powdered sugar Varroa control treatments on A. mellifera colony development.� Journal of Apicultural Research, 40 (3-4); 105-109 2001.

19.�� MACEDO, PA.� Wu. J: Ellis, MD.� Using inert dusts to detect and assess varroa infestations in honey bee colonies J APICULT RES. 41 (1-2): 3-7 2002.

Acknowledgments Of Assistance With Thanks

Dr Wendy Adams Ph.d

Arthur Adams

Robert Hickling B.E.M.

IBRA � International Bee Research Association, whose assistance made this paper possible.

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