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This is part two of this "Bee World" article
 
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The duration of the capped stage
 
Reduction of the average length of the capped stage is discussed as a
potential tolerance factor by several authors(35,56,62). Moritz and
Hanel(35) observed mature mite offspring in only 21% of worker brood cells
of A. m. capensis which has a capped stage approximately 2 days shorter
than A. m. carnica. A limitation in the population increase of varroa in A.
m. capensis colonies was confirmed by the investigation of Moritz and
Mautz(36).
 
Schousboe(56) measured maximum differences for the duration of the capped
stage of worker brood in A. m. ligustica coloniff of up to 1.15 days.
Buchler and Drescher(14) observed differences in the length of the capped
stage of up to 9 h between different strains (A. m. carnica, A. mellifera
and Buckfast) and up to 19 h between individual colonies. Aside from the
influence of the origin of the bees, seasonal effects were seen also,
confirmed in an investigation by Schousboe(57). Buchler and Drescher(14)
determined for 21 colonies, checked twice, a positive correlation between
the length of the capped stage and the infestation level (r =3D 0.48)
indicating that, on average, a reduction of the length of the capped stage
by one hour led to an 8.7% reduction in the final mite infestation level.
 
Testing small colonies of A. m. carnica, A. m. capensis and A. m.
scutellata in a flight room, Moritz(34) estimated the heritability of the
length of the capped stage (h2 =3D 0.8) and he observed a maternal effect
which was responsible for 23% of the total variance. However, B=FCchler and
Drescher(14) estimated the heritability for their test population of
European honey bee colonies under field conditions (h2 =3D 0.23) and got a
lower value, than the one given by Moritz(34).
 
Using a method involving a systematic exchange of brood between A. m.
caucasica, A. m. Iigustica and A. mellifera colonies, Le Conte and
Cornuet(23) were able to distinguish between the effects of the inherited
properties of the brood and colony-specific brood rearing effects on the
duration of the capped stage. They found a similar potential for both
factors and a heterosis effect (hybrid vigour) was noted for the resulting
hybrid bees.
 
In order to quantify the effect of differences in the capped stage on the
reproduction rate of V. jacobsoni, Langenbach(28) checked brood cells at 4h
intervals for the number and stages of offspring mites present. Because
some juvenile mites died and normal development was delayed, only 0.8
daughter mites were present on average at the time of emergence in European
races. This result is confirmed by Boecking and Dresche(5) who checked the
number of mite exuviae (cast off skins) during cell emergence and found
this method to be a reliable way to determine the true number of offspring.
 
If a rate of 0.8 daughters is used, a reduction in the developmental time
by 1 h may reduce the number of offspring by 0.9%. Multiplied over several
brood cycles, this relatively low reduction may cause remarkable
differences in infestation levels.
 
Different methods are described for the measurement of the length of the
capped stage in the cited studies. They include marked transparent sheets,
photography(14) (fig. 8) or marking cell cappings(28).
 
 
Varroa tolerance in selection programmes
 
In principle, all characters for which a correlation with the
susceptibility of the colonies can be demonstrated may be useful in
breeding programmes to increase varroa tolerance. Breeding success depends
on the real effect of the selection criterion, the accuracy and
repeatability of the test methods, on the genetic variation, on the
heritability and on the genetic and environmental interaction. For
practical breeding purposes, the complex of all these factors has to be
considered, and a compromise between the realizable population size and
testing effort, and the progress in selection that can be expected has to
be found. The most important information obtained from a discussion of the
different tolerance characteristics are summarized in table 1 . General
recommendations can rarely be given since=20the circumstances vary widely fo=
r
different breeders, and important basic data about individual
characteristics are still unknown.
 
A short report on existing selection programmes to increase varroa
tolerance is given here:
 
* The Yugoslavian programme run by Kulincevic et al (27) has been mentioned
previously. A bi directional selection for high and low brood infestation
with fertile mites was made over five generations. Significant differences
in all generations proved the heredity and selectability of this
characteristic. Because of the small population size, about 20 colonies,
and a genetic reduction caused by heavy colony losses in the second
generation, the genetic variability was too low for long lasting selection
progress. The practical use of the selected line will, therefore, probably
be low (see also(44)).
 
* Wilde and Koeniger(61) reported on a recent breeding programme to reduce
the duration of the capped stage of A. m. carnica by an introduction of A.
m. capensis genes. Out of 42 A. m. capensis queens inseminated with a
homogeneous carnica sperm mixture, the queen with the shortest brood
development period was selected in the parental generation. The daughter
queens were again inseminated with carnica sperm, and four filial
generations with an increasing population size were selected in the same
manner. The mean length of the capped stage in the population tended more
and more towards the A. m. camica standard from generation to generation,
but individual queens with A. m. capensis-like values were found in each
generation. Obviously, a large number of genes influence this
characteristic, and it is an open question as to what extent the relevant
A. m. capensis genes are accumulating in the A. m. carnica like back
crosses. No experience about the practical value of the selected stock is
available at present.
 
* Wallner, a professional beekeeper in Austria, checks the infestation
development of his 700 colonies by taking brood samples. At the end of the
season dead mites from colonies which showed a slow increase in infestation
are checked for the occurrence of damage. Over three generations he
selected colonies for breeding that had a high number of damaged mites
(60). He offers supposedly varroa-tolerant offspring from these colonies.
However, an objective evaluation using standardized conditions has not yet
been made.
 
* Varroa tolerance is the main selection criterion for the breeding stock
at the Hessian Bee Institute in Kirchhain, Germany (144 colonies)(12). In
December, colonies receive a uniform initial infestation of about 100
mites, and in the following August the total infestation is determined
using an acaricide treatment and counting dead mites. In addition, the
number of damaged mites is checked during June and July, and the brood
removal behaviour is tested. For experimental purposes, drones are selected
for insemination on the basis of the duration of their capped stage. The
progress made so far in this selection programme cannot be measured, but a
comparatively high tolerance in the Kirchhain stock has been demonstrated
under field conditions(9).
 
 
Recommendations and future options
 
The relevant characteristics of varroa tolerance in honey bees seem by now
to have been largely identified. Known testing methods can certainly be
improved in the future, but they already allow for a minimum
standardization of colony screening.
 
It is not clear in most cases how certain characteristics affect the
susceptibility under ceteris paribus conditions, i.e. without the influence
of other characteristics and interactions between different characteristics.
 
Recently Fries et al(22) reviewed scientific findings on the reproductive
biology and population dynamics of V. jacobsoni and developed a complex
mathematical model, which allows you to vary and check the influence of
single factors on the mite population development. With reference to this
theoretical study a more important effect can be expected from factors
which primarily influence the production of progeny over the life time of
the mite (for example mite fertility and number of reproductive cycles)
than from factors which primarily influence the length of time between two
reproductive cycles (for example brood attractiveness and brood removal
behaviour).
 
Much research has to be done to evaluate the genetic parameters of the
different characteristics. We have no or little information about the
genetic variation, the heritability and the contribution of additive
genetic, heterosis and maternal effects on the observed heredities. This
information must be available if reliable recommendations for breeding
schemes are to be given, and they are needed to estimate the progress in
selection which can be expected and to calculate the required population
size.
 
The designs of existing selection programmes were mainly planned with
regard to management aspects, and they are not optimized on a scientific,
genetic basis. To reach a high efficiency, this should be corrected as soon
as possible.
 
Permanent progress in selection can only be achieved in large populations.
Although no precise colony numbers can be defined at the moment, a minimum
population size of several hundred colonies is assumed to be needed. Under
existing
 
It is not clear in most cases how certain characteristics affect the
susceptibility under ceteris paribus conditions, i.e. without the influence
of other characteristics and interactions between different characteristics.
 
Recently Fries et al(22) reviewed scientific findings on the reproductive
biology and population dynamics of V. jacobsoni and developed a complex
mathematical model, which allows you to vary and check the influence of
single factors on the mite population development. With reference to this
theoretical study a more important effect can be expected from factors
which primarily influence the production of progeny over the life time of
the mite (for example mite fertility and number of reproductive cycles)
than from factors which primarily influence the length of time between two
reproductive cycles (for example brood attractiveness and brood removal
behaviour).
 
Much research has to be done to evaluate the genetic parameters of the
different characteristics. We have no or little information about the
genetic variation, the heritability and the contribution of additive
genetic, heterosis and maternal effects on the observed heredities. This
information must be available if reliable recommendations for breeding
schemes are to be given, and they are needed to estimate the progress in
selection which can be expected and to calculate the required population
size.
 
The designs of existing selection programmes were mainly planned with
regard to management aspects, and they are not optimized on a scientific,
genetic basis. To reach a high efficiency, this should be corrected as soon
as possible.
 
Permanent progress in selection can only be achieved in large populations.
Although no precise colony numbers can be defined at the moment, a minimum
population size of several hundred colonies is assumed to be needed. Under
existing beekeeping practice in most parts of Europe, the co-operation of
several breeders within breeding associations is therefore an imperative
requirement. These breeding unions need to define a common selection target
and have to perform tests under comparable conditions. For an optimal
evaluation of the test data, the genetic relationships between all members
of the population have to be considered for the breeding value of
individual queens. A first approach in this direction, which is standard
practice in animal breeding nowadays is used by the Austrian Carnica
Association and is being initiated in Germany by Bienefeld and Pritsch(1).
A large dataset is a basic requirement for estimating heritabilities and
genetic correlations with satisfactory precision.
 
Testing and selection for varroa tolerance undoubtedly needs a greater
effort than, for example, selection for honey productivity. There is a
definite need, therefore, to use positively selected bees on a large scale.
International co-operation across political and geographical borders has to
be promoted. Selected lines, for example from Austria or Germany, could
immediately be tested in other countries to check the potential of a
'European bee'. Instead of parallel and independent selection for varroa
tolerant bees in many small populations, improvements in a few large
populations are much more promising.
 
 
References
 
The numbers given at the end of references denote entries in Apicultural
Abstracts.
 
1. BIENEFELD, K; PRITSCH, G (1992) Kooperation zwischen Z=FCchtern und
zentrale Auswertung: Ans=E4tze f=FCr eine erfolgreiche Zucht der Honigbiene.
Die Biene 128(8): 443-447.
 
2. BIENEFELD, K; STROH, A M (1992) Einfl=FCsse der m=FCtterlichen Abstammung
der Bienenbrut (Apis mellifera) auf die Reproduktion von Varroa jacobsoni.
Annales Universitatis Mariae Curie-Sklodowska 47: 123-126.
 
3. BOECKING, O; DRESCHER, W (1991) Response of Apis mellifera L colonies to
brood infested with Varroa jacobsoni Oud.
Apidologie 22(3): 237-241.         563/92
 
4. BOECKING, O; DRESCHER, W (1992) The removal response of Apis mellifera L
colonies to  brood in wax and plastic cells after artificial and natural
infestation with Varroa jacobsoni Oud. and to freeze killed brood.
Experimental and Applied Acarology 16: 321 -329.
 
5. BOECKING, O; DRESCHER, W (1993) Reproductive success of Varroa jacobsoni
in worker 1. brood cells with regard to the duration of the post-capping
stage.
Journal of Apicultural Research (submitted).
 
6. B=DCCHLER(1989) Attractivity and reproductrive suitability for the
Varroa-mite of bee brood from different origin.
Proceedings of a meeting of the EC-experts group, Udine, Italy; 1988 139-145=
=2E
 
7. B=DCCHLER, R (1990) Possibilities for selecting increased Varroa toleranc=
e
in central European honey bees of different origins.
Apidologie 21(4): 36367.   0221/91
 
8. B=DCCHLER, R (1992) Test auf Varroatoleranz im Rahmen von Leistungspr=FCf=
ungen.
Neue Bienen Zeitung 3(3):162-167.  228/93
 
9. B=DCCHLER, R (1992) Zucht auf Varroatoleranz.
Deutsches Imker-Joumal 3(2): 43-50.
 
10 B=DCCHLER, R (1992) Die Auswirkung einer Brutunterbrechung auf
Reproduktion und =DCberleben zugegebener Varroa-Milben.
Annales Universitatis Mariae Curie-Sklodowska 47: 13-18.
 
11 B=DCCHLER, R (1993) Rate of damaged mites in natural mite fall with regar=
d
to seasonal effects and infestation development.
Apidologie 24(5): 492-493.
 
12 B=DCCHLER, R (1993) Aufbau, Leistungspr=FCfung und Selektion der Kirchhai=
ner
Population.
Die Biene 129(1): 11-17
 
13 B=DCCHLER, R (1994) Die Entwicklung varroatoleranter Honigbienen unter
nat=FCrlichen und z=FCchterischen Auslesebedingungen.
Die Biene (in preparation).
 
14 B=DCCHLER, R; DRESCHER, W (1990) Variance and heritability of the capped
developmental stage in European Apis mellifera L and its correlation with
increased Varroa jacobsoni Oud. infestation. Joumal of Apicultural Research
29(3): 172-176.   1362/91
 
15. B=DCCHLER, R; DRESCHER, W; TORNIER, I (1992) Grooming behaviour of Apis
cerana, Apis mellifera and Apis dorsata and its effects on the parasitic
mites Varroa jacobsoni and Tropilaelaps clareae.
Experimental and Applied Acarology 16: 313-319.
 
16. CAMAZINE, S (1986) Differential reproduction of the mite,Varroa
jacobsoni (Mesostigmata: Varroidae), on Africanized and European honey bees
(Hymenoptera: Apidae). Annals of the Entomological Society of Amenica
79(5): 801-803.     238/88
 
17. DE JONG, D (1988) Varroa jacobsoni does reproduce in worker cells of
Apis cerana in South Korea.
Apidologie 19(3): 241-243.   1139/39
 
18. DE JONG, D; GONCALVES, L S; MORSE, R A (1984) Dependence on climate of
the virulence of Varroa jacobsoni.
Bee World 65(3):117-121.   958/85
 
19. ENGELS, W; GONCALVES, L S; STEINER, J; BURIOU A, A H; CAVICHIO ISSA, M
R (1986) Varroa-Befall von carnica-V=F6lkern in Tropenklima.
Apidologie 17(3): 203-216.   983/87
 
20. FUCHS, S (1992) Ein Testverfahren zum Vergleich der
Varroatoseanf=E4l1igkeit in kleinenVolkseinheiten.
Annales Universitatis Mariae Curie-Sklodowska 47: 127-132.
 
21. FUCHS, S; BIENEFELD, K (1991) Testing susceptibility to varroatosis in
small bee units.
Apidologie 22(4): 463-465.   591/92
 
22. FRIES, I; CAMAZINE, S, SNEYD, J (1994) Population dynamics of Varroa
jacobsoni: a model and a review,
Bee World 75(1): 5-28
 
23. HOFFMANN, S (1993) Personal communication.
 
24. HOFFMANN, S (1993) The occurrence of damaged mites in cage test and
under field conditions in hybrids of different Carniolan lines. Apidologie
24: 493-495.
 
25. KOENIGER, N; KOENIGER, G; WIJAYAGUNASEKARA, N H P (1981) Beobachtungen
=FCber die Anpassung von Varroa jacobsoni an ihren nat=FCrlichen Wirt Apis
cerana in Sri Lanka.
Apidologie 12(1): 37-40.     72182
 
26. KULINCEVIC, J M; RINDERER, T E; UROSEVIC, D J (1988) Seasonality and
colony variation of reproducing and non-reproducing Varroa jacobsoni
females in Westem honey bee (Apis mellifera) worker brood.
Apidologie 19(2): 173-179.   600/89
 
27. KULINCEVIC; J M; RINDERER, T E; MLADJAN, V J; Buco, S M (1992) Five
years of bi-directional genetic selection for honey bees resistant and
susceptibility to Varroa jacobsoni.
Apidologie 23(5): 443-452.  1305/93
 
28 LANGENBACH, K (1992) Die Auswirkung der Zellverdeckelungsdauer auf den
Reproduktionserfolg von Varroa jacobsoni in Bienenbrutzellen.
Report at the meeting of the German bee research institutes, Lehnitz/Hohen
Neuendorf, Germany; 26 March 1992.
 
29 CONTE, Y; CORNUET, J M (1989) Variability of the postcapping stage
duration of the worker brood in three different races of Apis mellifera.
Proceedings of a meeting of the EC-experts group, Udine, Italy 1988: 171-174=
=2E
 
30. MARCANGEU, J M; EGUARAS, M J; FERNANDEZ, N A Reproduction of Varroa
jacobsoni (Acari: Mesostigmata: Varroidae) in temperate climates of
Argentina.
Apidologie 23(1): 57-60.   226/93
 
31 MOOSBECKHOFER, R (1992) Beobachtungen zum Auftreten besch=E4digter
Varroamilben im nat=FCrlichen Totenfall bei V=F6lkem von Apis mellifera carn=
ica.
Apidologie 23: 523-531.
 
32. MORETTO, G; GONCALVES, L S; DE JONG, D; BICHUETTE, M Z (1991) The
effects of climate and bee race on Varroa jacobsoni Oud. infestations in
Brazil.
Apidologie 22(3):197-203.   564/92
 
33. MORETTO, G; GONCALVES, L S; DE JONG, D (1991) Africanized bees are more
efficient at removing Varroa jacobsoni-preliminary data.
American Bee Journal 131(7): 434.   5661/92
 
34. MORITZ, R F A (1985) Heritability of the post- capping stage in Apis
mellifera and its relation to varroatosis resistance.
Joumal of Heredity 76: 267-270.    854/87
 
35. MORITZ F A; H=C4NEL H (1984) Restricted development of the parasitic mit=
e
Varroa jacobsoni Oud. in the Cape honeybee Apis mellifera capensis Esch.
Zeitschriftt f=FCr Angewandte Entomologie 97(1): 915.   2431/85
 
36. MORITZ, R F A; MAUTZ, D (1990) Development of Varroa jacobsoni in
colonies of Apis mellifera capensis and Apis mellifera carnica.
Apidologie 21(1): 53-58.    1292/90
 
37. OTTEN, C (1991) Vergleichende Untersuchungen zum Populationswachstum
von Varroa jacobsoni Oud. in V=F6lkern von Apis mellifera L unterschiedliche=
r
geographischer Herkunft.
Dissertation: Johann Wolfgang Goethe Universitat, Frankfurt, Germany; 203 pp=
=2E
 
38. OTTEN, C (1991) Factors and effects of a different distribution of
Varroa jacobsoni between adult bees and bee brood.
Apidologie 22(4): 465-467.  5921/92
 
39. OTTEN, C; FUCHS, 5 (1 990) Seasonal variations in the reproductive
behavior of Varroa jacobsoni in coloniff of Apis mellifera carnica, A. m.
ligustica and A. m. mellifera.
Apidologie 21(4): 367-368.   1021191
 
40. PENG, Y-S; FANG, Y; XU, S; GE, L (1987) The resistance mechanismen of
the Asian honey bee, Apis cerana Fabr. to an ectoparasitic mite, Varroa
jacobsoni Oudemans.
Journal of Invertebrate Pathology 49(1):54-60.   463/88
 
41 PENG, Y-S C; hNG, Y; XU, S; GE, L; NASR, M E
(1987) Response of foster Asian honeybee (Apis cerana Fabr.) colonies to
the brood of European honeybee (Apis mellifera L.) infested with parasitic
mite, Vanroa jacobsoni Oudemans.
Journal of Invertebrate Pathology 49: 259-264.     628/88
 
42. RATH, W (1991) Laboratory culture of the mites Varroa jacobsoni and
Tropilaelaps clareae.
Experimental and Applied Acarology 10(3/4): 289-293.        597/93
 
43. RATH, W; DRESCHER, W (1990) Response=20of Apis cerana Fabr. colonies
towards brood infested with Varroa jacobsoni Oud. and infestation rate of
colonies in Thailand.
Apidologie 21(4): 311-321.   847/91
 
44. RINDERER, T E; GUZMAN, L l; KULINCEVIC, J M; DELATTE, G T; BEAMAN, L D;
Buco, S M (1993) The breeding, importing, testing and general
characteristics of Yugoslavian honey bees bred for resistance to Varroa
jacobsoni.
American Bee Journal 133(3): 197-200.
 
45. RITTER, W (1990) Development of the Varroa mite populations in treated
and untreated colonies in Tunisia.
Apidologie 21: 368-370.
 
46. RITTER, W, DE JONG, D (1984) Reproduction of Varroa jacobsoni 0. in
Europe, the Middle East and tropical South America.
Zeitschrift fur Angewandte Entomologie 98(1):55-57.   572/85
 
47. RITTER, W; BOECKING; O (1994) Grooming and removal behavior of Apis
mellifera intermissa in Tunisia regarding Varroa jacobsoni.
Journal of Apicultural Research (submitted).
 
48. ROSENKRANZ, P (1992) Personal Communication.
 
49. ROSENKRANZ, P; STURMER, M (1992) Ern=E4hrungsabh=E4ngige Fertilit=E4t de=
r
Varroa-Weibchen in Arbeiterinnen-Brut von Apis mellifera
carnica und Apis mellifera capensis
Annales Universitatis Mariae Curie-Sklodowska 47: 55-60.
 
50. ROSENKRANZ, P; RACHINSKY, A, STRAMBI, A; STRAMEI, C; ROSTORF, P (1 990)
Juvenile hormone titer in capped worker brood of Apis mellifera and
reproduction in the bee mite Varroa jacobsoni.
General and Comparative Endocrinology78: 189-193.  1364/91
 
51. ROSENKRANZ, P; TEIIVARSON, N C; SINGH, A; ENGELS, W (1993) Differential
hygenic behaviour towards Varroa jacobsoni in capped worker brood of Apis
cerana depends on alien scent adhering to the mites.
Journal of Apicultural Research 32: 89-93.
 
52. ROTHENBUHUER, W (1964) Behavior genetics of nest cleaning behavior in
honeybees. I. Responses of four inbred lines to disease killed brood.
Animal Behavior 12:578-583.
 
53. RUTTNER, F (1991) Auf dem Wege zu einer varroatoleranten Carnica.
Allgemeine Deutsche Imkerzeitung 25(1): 10-15.
 
54. RUTTNER, E; HANEL, H (1992) Active defense against Varoa mites in a
Carniolan strain of honeybee (Apis mellifera carnica Pollmann).
Apidologie 23(2): 173-187.   592/93
 
55. RUTTNER, F; MARX, H; MARX, G (1984) Beobachtungen =FCber eine m=F6gliche
Anpassung von Varroa jacobsoni an Apis mellifera L. in Uruguay.
Apidologie 15(1): 43-62.    961/85
 
56. SCHOUSBOE, C (1986) The duration of sealed cell stage in worker
honeybee brood (Apis mellifera L) in relation to increased resistance to
the Varroa mite (Varroa jacobsoni Oud.).
Tidsskrift for Planteavl 90:293-299.       806/88
 
57. SCHOUSBOE, C (1990) Seasonal variation in duration of capped stage in
worker bee brood.
Tidsskrift for Biavl 124(2): 50-52.
 
58. TEWARSON, N C; SINGH, A; ENGELS; W (1992) Reproduction of Varroa
jacobsoni in colonies of Apis cerana indica under natural and experimental
conditions.
Apidologie 23(2):161-171.   450/93
 
59. THRYBOM, B; FRIES, I (1991) Development of infestations by Varroa
jacobsoni in hybrid colonies of Apis mellifera monticola and Apis mellifera
ligustica.
Journal of Apicultural Research 30(3/4): 151-155.   1417/92
 
60. WALLNER, A (1993) Mein Weg in der Varroaresistenz=FCchtung.
Bienenvater 1 14(3): 107-108.
 
61. WILDE, J; KOENIGER, N (1992) Selektion auf Verk=FCrzung der
Zellverdeckelungsdauer (ZVD) der Arbeiterinnenbrut von Apis mellifera
carnica.
Annales Universitatis Mariae Curie-Sklodowska 47: 133-136.
 
62. WOYKE, J (1989) Breeding of honey bees resistant to Varroa jacobsoni.
American Bee Journal 129(1): 21-23.  1253/89
 
[This review was presented at IBRA's East European workshop on varroa (see
p. 81)-Ed.]
 
 
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