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# Small-cell comb does not control Varroa mites in colonies of honeybees of European origin

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We tested the idea that Varroa destructor can be controlled in colonies of the European subspecies of Apis mellifera by providing them with combs built of small cells, in which immature mites might have difficulty developing for lack of space. We established seven pairs of equal-size colonies that started out equally infested with mites. In each pair, one hive contained only standard-cell (5.4mm) comb, and the other contained only small-cell (4.8mm) comb. We measured the colonies' mite loads at monthly intervals across a summer. No differences arose between the two treatment groups in their mean mite loads (mites per 100 worker bees or mite drop per 48h). We suggest that providing small-cell combs did not inhibit mite reproduction because the fill factor (thorax width/cell width) was only slightly higher in the small cells than in the standard cells (79% and 73%, respectively). Keywords Apis mellifera – Varroa destructor –small cell–mite control–cell size
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Small-cell comb does not control Varroa mites in
colonies of honeybees of European origin
Thomas Seeley, Sean Griﬃn
To cite this version:
Thomas Seeley, Sean Griﬃn. Small-cell comb does not control Varroa mites in colonies of
honeybees of European origin. Apidologie, Springer Verlag (Germany), 2011, 42 (4), pp.526-
532. <10.1007/s13592-011-0054-4>. <hal-01003589>
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Small-cell comb does not control Varroa mites in colonies
of honeybees of European origin
Thomas D. SEELEY, Sean R. GRIFFIN
Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA
Received 9 July 2010 Revised 26 September 2010 Accepted 4 October 2010
Abstract We tested the idea that Varroa destructor can be controlled in colonies of the European subspecies
of Apis mellifera by providing them with combs built of small cells, in which immature mites might have
difficulty developing for lack of space. We established seven pairs of equal-size colonies that started out equally
infested with mites. In each pair, one hive contained only standard-cell (5.4 mm) comb, and the other contained
only small-cell (4.8 mm) comb. We measured the colonies' mite loads at monthly intervals across a summer. No
differences arose between the two treatment groups in their mean mite loads (mites per 100 worker bees or mite
drop per 48 h). We suggest that providing small-cell combs did not inhibit mite reproduction because the fill
factor (thorax width/cell width) was only slightly higher in the small cells than in the standard cells (79% and
73%, respectively).
Apis mellifera / Varroa destructor / small cell / mite control / cell size
1. INTRODUCTION
The mite Varroa destructor is a new parasite of
European honeybees living in North America,
having been introduced to these bees only in the
mid-1980s (Wenner and Bushing 1996;Sanford
2001). This mite and its associated viruses are a
major cause of colony mortality worldwide. As a
rule, if a colony of European honeybees does not
receive mite control treatments, the mite popula-
tion will grow from just a few mites to several
thousand mites in 3 to 4 years, ultimately killing
the colony (Ritter 1988; Korpela et al. 1992;
Wenner and Thorp 2002). One possible non-
chemical method of mite control that has been
much discussed and debated (e.g., Erickson et al.
1990;Johnsen2005) is to reduce worker cell
width from the current size of 5.25.5 to 4.9 mm.
It has been suggested (e.g., Medina and Martin
1999) that smaller cells may cause higher
mortality of immature mites, because the mites
develop directly beside immature bees in cells
(Don and Guerin 1997) so a smaller space
between the developing bee and the cell wall
might hamper the movements of the immature
mites, reducing their ability to feed and thereby
raising their mortality.
One study that has provided support for the
concept of small-cell combs for Varroa mite
control was conducted in South Africa with
African honeybees (Martin and Kryger 2002).
Colonies were established in which larger bees
(Apis mellifera capensis, similar in size to
European bees) and smaller bees (A. m. scutel-
lata, smaller than European bees) were reared
together in small-cell (4.6 mm) combs, and it
was found that both mother mite mortality and
male offspring mite mortality were higher in the
cells with larger bees. The authors report that
mother mites and male protonymphs appeared
to get trapped in the upper part of the cells that
contained the larger bees, thereby preventing the
Corresponding author: T.D. Seeley,
tds5@cornell.edu
Manuscript editor: Marla Spivak
Apidologie (2011) 42:526532
Original article
* INRA, DIB-AGIB and Springer Science+Business Media B.V., 2011
DOI: 10.1007/s13592-011-0054-4
mites from reaching the feeding site on the
abdomen of the developing bee pupa. This is,
however, a special case in which some of the
largest worker bees found in A. mellifera were
reared in some of the smallest cells produced by
A. mellifera, and it may be that the elevated
mite mortality that was observed requires such
extreme conditions.
A second relevant study is that of McMullan
and Brown (2006). Working with A. m. melli-
fera in Ireland, they gave colonies small-cell
(5.04 mm) combs and standard-cell (5.48 mm)
combs and found that the worker bees reared in
the small-cell combs were less than 1% smaller
(in head width and thorax width) than those
reared in the standard-cell combs, even though
the small cells were 8% less wide than the
standard cells. Evidently, when bees are reared
in small cells, the reduction in bee size is not
proportional to the reduction in cell size, so the
cell fill factor (thorax width/cell width,
expressed as a percentage) is higher and there
is less room for the mites. McMullan and
Brown (2006), for example, found that the fill
factor was 73% in colonies with standard-cell
combs but 79% in ones with small-cell combs.
Three recent studies conducted either in the
southeastern USA (Ellis et al. 2009; Berry et al.
2010) or in Ireland (Coffey et al. 2010) have
directly tested the idea that giving combs of
small cells to colonies of European honeybees
will reduce their susceptibility to Varroa. All
three studies found no evidence that providing
colonies with small-cell combs rather than
standard-cell combs impedes reproduction by
Varroa. A fourth recent study on this subject,
conducted in New Zealand (Taylor et al. 2008)
also found no effect of cell size on mite
infestation, but this fourth study was confound-
ed by difficulty in getting the bees to build
combs consisting entirely of small cells, result-
ing in small differences in cell size between the
two treatment groups. In the present study, we
extended this work by conducting a test in the
northeastern USA in which we established pairs
of colonies, with each pair consisting of one
colony living in a hive containing standard-cell
combs and one colony living in a hive contain-
ing small-cell combs. To be certain that the
small-cell combs in our study consisted entirely
of small cells, we used small-cell combs built of
plastic. The two colonies in each pair were
started as artificial swarms made from the same
source colony and with closely matched mite
bees in the paired colonies at monthly intervals
across a summer to see if the colonies living in
hives equipped with small-cell combs showed
signs of reduced reproduction by the mites.
2. MATERIALS AND METHODS
The study was conducted over the summer of
2009 in Ithaca, NY, USA. On June 2, we prepared 14
1.0-kg (=approximately 7,700 bees) packages of
honeybees, 2 from each of 7 strong colonies that
hadscoredhighlyinaVa r r o a mite drop test
conducted 6 weeks earlier, on April, 1820; 77, 26,
34, 66, 53, 55, and 37 mites per colony collected on a
sticky board in 48 h. We did not treat the seven
source colonies for mites before we shook the bees
from them for our packages, so we could be confident
that the bees in our packages were well infested with
mites. We could also be confident that both packages
in a pair had similar numbers of mites (this was also
checked, as described below) because the bees in
each pair of packages came from the same source
colony. Each package was given a new Minnesota
Hygienic queen (Olivarez Honey Bees, Inc., Chico,
CA, USA).
Immediately after making the packages, we began
feeding them with a 50/50 (v/v) sucrose solution
brushed onto the wire screen of one side of each
package cage. We continued this feeding for the next
3 days, June 35. On the evening of June 5, we
installed each package in a single-story deep Lang-
stroth hive containing ten frames of comb. One
package in each pair was installed in a hive
containing frames of standard-cell comb built of
beeswax, and the other package in each pair was
installed in a hive containing frames of small-cell
comb built of plastic (Honey Super Cell, Westmor-
land, CA,USA). (Note: We used plastic combs to be
certain that the colonies that received the small-cell
treatment had only small cells in their combs. We
Small-cell comb does not control Varroa mites 527
failed in two attempts in 2007 and 2008 to get our
bees to build beeswax combs consisting entirely of
small cells by giving them frames containing small-
cell foundation (4.9 mm, Dadant and Sons, Hamilton,
IL, USA).) There were no drone cells in any of the
frames of comb used in this study. We measured the
mean width of the cells in each hive by measuring the
width of ten cells in a straight line (inclusive of wall
widths) in the center of one side of each frame of
comb. For the seven hives with standard-cell combs,
the mean cell widths were 5.38, 5.40, 5.40, 5.36,
5.39, 5.38, and 5.38 mm, hence 5.38 mm on average.
For the seven hives with small-cell combs, the mean
cell widths were all the same: 4.82 mm. Thus, there
was a mean reduction in cell width in the small-cell
combs of 0.56 mm, or 10.4% (0.56/5.38=0.104).
Both groups of hives (those with standard-cell
combs or small-cell combs) were located at the
Liddell Field Station, but were arranged in separate
apiaries spaced 120 m apart. Within each apiary,
adjacent hives were spaced 5 m apart. We put all the
colonies in the same general area to minimize
location effects on any differences we might find
between the two group, but in different apiaries to
minimize transmission of Varroa mites between the
two groups. We managed the colonies for honey
production, giving each one a second deep hive body
containing frames of standard-cell or small-cell
combs in early July to prevent swarming and to
provide more space for brood rearing and honey
storage.
Once a monthfrom mid-June to mid-October
we took measurements of three variables: (1) the
strength of each colony, (2) the infestation level of
Varroa mites in each colony, and (3) the size of the
workers in each colony. To measure colony strength,
we counted the number of frames of adult bees and
brood in each colony, doing so by visually examining
each side of each comb and estimating what fraction
(1/4, 2/4, 3/4, or 4/4) was covered with adult bees and
what fraction was filled with brood. To measure the
level of the Varroa mite infestation, we used two
methods. First, 26 days before we opened the hives
for the detailed visual inspections, we installed in
each hive a sticky board (Dadant and Sons, Hamilton,
IL, USA) for 48 h to get a 48-h mite drop count.
Second, when we opened the hives to inspect the combs
of each colony, we collected from the brood region of
each colony's nest a sample of 250 mL of bees
(approximately 300 bees) and used the powdered
sugar method to determine the number of mites on
these bees. (The bees and mites from each colony were
returned to it after we made our measurement.) To
measure the size of the workers in each colony, each
time we made a visual inspection of a colony, we
collected from its brood nest region a sample of ten
worker bees and measured each bee's head width
(±0.02 mm) using a dissecting scope equipped with an
ocular micrometer. In the summer of 2010, we
measured the thorax widths of bees collected from
the five surviving colonies with standard-cell combs
and from two new colonies with small-cell combs. All
the original colonies with small-cell combs died over
the winter of 20092010, so we set up two colonies on
small-cell combs in spring 2010, to get bees reared in
small-cell combs for thorax width measurements.
When we took our monthly measurements of the
colonies, we cut out any drone comb that the colonies
had built, usually along the bottoms of the frames. At
most, this involved removing 25 drone cells per
colony per inspection; none of the drone comb
contained drone brood. In this way, we prevented
drone rearing in our colonies and this meant that all
the mite reproduction in our study colonies occurred
in cells of worker brood. This ensured that our
measurements of the number of Varroa mites in our
colonies would reflect a difference, if any, in mite
reproduction between hives equipped with just
standard-size worker cells and just small-size worker
cells.
All descriptive statistics are reported as the mean±
SE. To test for differences between the means of
variables measured in both the standard-cell and the
small-cell colonies, we used paired comparisons t
tests (Sokal and Rohlf 1981) to take advantage of the
initial pairing of the study colonies.
3. RESULTS
3.1. The two treatment groups started
with matching distributions of mites
per colony
To see if the two treatment groups started out
well matched in terms of numbers of mites per
colony, we checked whether the initial counts of
528 T.D. Seeley and S.R. Griffin
mites per 100 adult bees were similar for the
two colonies produced from each of the seven
source colonies. Figure 1 shows that there were
differences in mean mite load among the seven
pairs of colonies, but that the two colonies in
each pair were closely matched in their mite
parisons t test, t
6
=1.24, P>0.25). It is clear,
therefore, that the two treatment groups started
out with virtually identical distributions of mites
per colony.
3.2. The two treatment groups ended
the summer with similar
mite infestations
Table I summarizes our findings regarding
the mite loads in the colonies of the two
treatment groups, measured in terms of mites
per 100 adult bees. It shows that for both
treatment groups, the mite loads started at a
relatively high level in June, then dropped to
lower levels in July and August, and eventually
increased in September and October. At no
point did we detect a difference in number of
mites per 100 adult bees between the colonies
living on standard-cell combs and those living
on small-cell combs.
Table II summarizes our findings regarding
the mite loads in the colonies of the two
treatment groups, measured in terms of mites
caught on sticky boards over a 48-h period
(=mite drop count). It shows that for both
treatment groups, the mean mite drop count rose
gradually over the summer and that the mean
mite drop count never differed significantly
between the two groups. The mean mite drop
counts were slightly lower (though not signifi-
cantly so) for the small-cell colonies in July,
August, September, and October, but we suspect
that this trend was a result of the small-cell
colonies being smaller than the standard-cell
colonies. The colonies in the hives with the
plastic, small-cell combs grew noticeably less
rapidly than those in the h ives with the
beeswax, standard-cell combs. For example, by
the middle of August, the mean numbers of
frames of adult bees and frames of brood in the
small-cell colonies were only 4.2±0.7 and 3.0±
0.4, whereas in the standard-cell colonies they
were 7.7±0.8 and 5.5±0.5.
To compensate for the difference in mean
colony size between the treatment groups, we
divided each colony's mite drop count by the
number of frames of adult bees. This yielded a
value of mites/sticky board/48 h/frame of bees.
The results are summarized in Table II.Wesee
(standard-cell comb colony)
84012
4
12
8
(small-cell comb colony)
Figure 1. Correlation plot that shows how the two
colonies in each pair of colonies used in the study
started out with similar loads of Varroa mites. The
two colonies in each pair were established using
1.0 kg of bees taken from the same mite-infested
source colony. In each pair, one colony was given
standard-cell combs and the other was given small-
cell combs.
Table I. Comparisons of the number of mites per 100
adult bees between colonies living on standard-cell
combs vs. small-cell combs.
Date Mites per 100 adult bees P value
Standard-cell Small-cell
June 16 6.48±1.00 7.14±1.12 >0.50
July 16 2.33± 0.58 3.33±0.79 >0.25
Aug 12 1.81±0.62 3.00±1.11 >0.50
Sept 19 4.71± 1.42 6.62±0.84 >0.15
Oct 17 6.45±0.83 8.43±1.00 >0.20
Small-cell comb does not control Varroa mites 529
that this correction for colony size differences
between the two treatment groups eliminates the
suggestion of fewer mites in the small-cell
colonies. Indeed, there is evidence that by the
end of the summer, in September and October,
the number of mites per adult bee was becoming
higher in the small-cell colonies than in the
standard-cell colonies.
Table III summarizes our findings regarding
worker bee head width across the summer for
bees in the standard-cell and the small-cell
colonies. We see that there was a slight
(approximately 0.08 mm, or 2.1%), but signif-
icant (P<0.01), reduction in head width in the
small-cell colonies, but that there was no change
in head width in the standard-cell colonies.
Table III also shows our findings regarding
worker bee thorax width for bees in the two
types of colony. We see that there was a slight
(approximately 0.14 mm or 3.5%), but signifi-
cant (P <0.01), difference in thorax width
between the two types of colonies.
4. DISCUSSION
Despite our hope that equipping colonies of
European honeybees with small-cell combs
would protect them from Varroa by inhibiting
the mite's reproduction, we found no evidence
of this in our study. We used manufactured
plastic combs for our small-cell treatment, and
we removed from all our hives any drone comb
that the bees built, so there can be no doubt that
the colonies in our small-cell treatment group
had only small cells (mean width 4.82 mm) in
their combs and that the colonies in our
standard-cell treatment group had only standard
cells (mean width 5.38 mm) in their combs.
Despite this unambiguous difference in cell size
between our two treatment groups, we found no
difference in number of mites per 100 worker
bees or in mite drop count between the two
treatment groups. If it were the case that Varroa
reproduction on European honeybees is imped-
ed when these mites parasitize bees living on
small-cell combs, then over the summer, we
should have seen a decline in the mite levels in
the small-cell colonies relative to the mite levels
in the standard-cell colonies. But we saw no
sign of such a decline. On the contrary, we
found that the mean mite counts started out the
same for the two groups of colonies and
remained indistin guishable over the next
4 months. We conclude that the small-cell
treatment did not hamper the growth of the
populations of Va r r o a mites in our study
colonies in the northeastern USA (NY state), a
conclusion that echoes those of two analogous
studies conducted in the southeastern USA
(Florida and Georgia) (Ellis et al. 2009; Berry
et al. 2010) and one study conducted in Ireland
that examined mite reproduction in small-cell
(4.91 mm) and standard-cell (5.38 mm) combs
(Coffey et al. 2010).
Likewise, our findings regarding the effect of
reducing cell size on bee size are consistent with
what McMullan and B rown (2006)have
reported. When they gave colonies either
small-cell (5.04 mm) combs or standard-cell
(5.48 mm) combs, they found that the bees
Table II. Comparisons of the counts of mites caught on a sticky board over 48 h between colonies living on
standard-cell combs vs. small-cell combs.
Date Mites/sticky board/48 h P value Mites/sticky board/48 h/frame of bees P value
Standard-cell Small-cell Standard-cell Small-cell
June 10 11.2±3.5 13.4±3.2 >0.50 5.12±1.80 4.65±1.27 >0.50
July 13 21.9±8.7 15.9±3.8 >0.50 7.33±3.12 6.19±1.49 >0.60
Aug 10 27.1±5.7 23.4±2.9 >0.40 3.61± 0.62 4.04±1.09 >0.60
Sept 17 46.1±10.6 39.0±12.4 >0.40 4.13±0.44 7.50±2.39 >0.50
Oct 16 55.6±10.1 52.1±11.4 >0.40 5.24±0.69 10.65±2.51 >0.15
530 T.D. Seeley and S.R. Griffin
reared in small-cell combs were only about 1%
smaller (in head width and thorax width) than
those reared in standard-cell combs, even
though the small cells were 8% less wide than
the standard cells. Similarly, we found that bees
reared in our small-cell combs (4.82 mm) were
only 2.1% smaller in head width and 3.5%
smaller in thorax width than those reared in our
standard-cell combs, even though our small
cells were 10.4% less wide than our standard
cells. It seems clear now that when bees are
reared in small cells, the reduction in bee size is
not proportional to the reduction in cell size.
The concept of small-cell combs as a non-
chemical means of Varroa mite control seemed
to be supported by the finding reported by
Martin and Kryger (2002) that when relatively
large worker bees (A. m. capensis) and relative-
ly small worker bees (A. m. scutellata) were
reared together in the small-cell (4.6 mm)
combs of A. m. scutellata, many fewer fertilized
females mites were produced in cells containing
the larger bees. They also reported that the low
reproductive success of mites in cells with the
larger bees was due to high levels of mother
mite and male protonymph mite mortality.
Martin and Kryger (2002) surmised that the
reason for the higher mite mortality in cells with
larger bees was a lack of space for the mites to
move aroun d inside the cells holding the big
bees. This may have occurred in the situation
studied by Martin and Kryger (2002), because
their investigation involved some of the largest
workers of A. mellifera (those of A. m. capensis)
being reared in some of the smallest cells of A.
mellifera (those of A. m. scutellata, approxi-
mately 4.6 mm wide).
It now seems highly doubtful, however, that
when workers of the European races of A.
mellifera are reared in small cells (4.8 mm, this
study; or 4.9 mm, Ellis et al. 2009, Berry et al.
2010, Coffey et al. 2010), the fill factor is high
enough to inhibit mite reproduction and so
achieve mit e control . We measured the fill
factor (the ratio of thorax width to cell width,
expressed as a percentage) for both the
standard-cell combs and the small-cell combs
in our study. The bees reared in our standard-
cell combs had a mean thorax width of 3.95 mm
and, thus, a fill factor of 3.95/5.38=73%,
whereas the bees reared in our small-cell combs
had a mean thorax width of 3.81 mm and, thus,
a fill factor of 3.81/4.82=79%. These values of
fill factor are identical to those reported by
McMullan and Brown (2006)forA. m. mellifera
in Ireland reared on standard-cell (5.48 mm) and
small-cell (5.04 mm) combs: 73% and 79%.
Because the fill factors were rather low for both
groups of bees, and only slightly higher for the
bees living on small-cell combs, it is perhaps not
surprising that we found no evidence in support
of the notion that small-cell combs hinder the
reproduction of mites on European honeybees.
ACKNOWLEDGMENTS
This research was supported by the US Department
of Agriculture (Hatch grant NYC-191522). We thank
Table III. Comparisons of the head widths and thorax widths of worker bees between colonies living on
standard-cell combs vs. small-cell combs.
Date Standard-cell Small-cell P value
16 June 2009 3.80±0.02 3.78±0.01 >0.50
16 July 2009 3.76±0.01 3.71±0.01 <0.01
12 Aug 2009 3.76±0.01 3.70±0.02 <0.01
19 Sept 2009 3.78±0.01 3.70±0.02 <0.01
17 Oct 2009 3.78±0.01 3.70±0.01 <0.01
Thorax width (mm)
7 Sept 2010 3.95±0.03 3.81±0.03 <0.01
Small-cell comb does not control Varroa mites 531
Professor Nicholas Calderone and two reviewers for
La diminution de la taille des cellules des rayons
ne réduit pas l'infestation par Varroa destructor
dans les colonies d'abeilles d'origine européenne.
Apis mellifera / Varroa destructor / taille de la
cellule / lutte anti-acarien / cellule réduite
Waben mit kleinen Zellen sind nicht geeignet um
den Varroabefall in Völk ern der europäischen
Honigbienen zu kontrollieren.
Apis mellifera / Varroa destructor / kleine Zellen /
Milbenkontrolle / Zellgröße
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532 T.D. Seeley and S.R. Griffin
... The interest in small-cell combs has been aroused by reports showing that the development of Varroa destructor parasite populations can be reduced by rearing brood in small-cell combs instead of standard-cell combs. With its global range, the V. destructor mite causes large colony losses, and is therefore the biggest and most common problem of modern apiculture [26][27][28]. To date, the reduction of the development of V. destructor populations in brood reared in small-cell combs has been confirmed in Europe [29], Argentina [30], and Brazil [31,32]. ...
... To date, the reduction of the development of V. destructor populations in brood reared in small-cell combs has been confirmed in Europe [29], Argentina [30], and Brazil [31,32]. In contrast, this has not been confirmed by studies conducted in the USA [28,33,34], New Zealand [35], and some studies carried out in Europe [36]. However, it has been shown that keeping colonies on small-cell combs exerts a significant effect on the morphological traits and the biology of worker bees. ...
... However, it has been shown that keeping colonies on small-cell combs exerts a significant effect on the morphological traits and the biology of worker bees. This results in a decrease in the thorax weight, head width and height, thorax width and length, width and length of fore wings, and width of the 3rd and 4th tergites [28,37,38]; additionally, it contributes to a higher effectiveness of hygienic behaviour [25] and a higher rate of springtime colony development [33] as well as extension of the lifespan of workers [39]. ...
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The efficiency of the hygienic behaviour in bee colonies towards dead brood was assessed in small-cell combs (SMCombs) and in standard-cell combs (STCombs). Each colony had both types of combs in the nest on a permanent basis. Simultaneous keeping of a colony on standard- and small-cell combs is a novel approach to the use of small-cell combs in beekeeping. The number of killed pupae removed within 24 h was the measure of the hygienic behaviour efficiency. Regardless of the year, the brood in the SMCombs was uncapped and removed significantly more efficient (p ≤ 0.01) than in the STCombs (number of non-uncapped cells: in 2020 SMCombs = 3.79, STCombs = 11.62; in 2021 SMCombs = 2.34, STCombs = 5.28 and completely removed cells: in 2020 SMCombs = 87.46, STCombs = 80.04; in 2021 SMCombs = 96.75, STCombs = 92.66). In colonies kept simultaneously on standard- and small-cell combs, the width of the comb cells has a significant effect on the efficiency of removal of dead brood, which is removed more efficient from small-cell combs than from standard-cell combs.
... Erickson et al. (1990) claimed that alterations of the comb cell width induced changes in the worker body size without selection and breeding. However, contradictory conclusions were formulated by McMullan and Brown (2006) and Seeley and Griffin (2011). McMullan and Brown (2006) found that a 7-8% reduction of comb cell width resulted in an only 1% decrease in the head and thorax width. ...
... McMullan and Brown (2006) found that a 7-8% reduction of comb cell width resulted in an only 1% decrease in the head and thorax width. Similar results were obtained by Seeley and Griffin (2011). This indicates that the bee body size is relatively constant, and the effect of the cell width on these parameters is lower than previously assumed (McMullan and Brown 2006;Seeley and Griffin 2011). ...
... Similar results were obtained by Seeley and Griffin (2011). This indicates that the bee body size is relatively constant, and the effect of the cell width on these parameters is lower than previously assumed (McMullan and Brown 2006;Seeley and Griffin 2011). ...
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The aim of the study was to investigate the impact of the combination of the colony type (kept on small-cell or standard-cell combs) and the width of worker comb cells (small-cell or standard-cell combs) on the body weight and morphometric traits of worker bees. The values of morphometric parameters of worker bees changed within a substantially lower range than the width of their rearing cells. This indicates that the worker body size is relatively constant, and manipulation with the cell width is not a good method for modeling the body size of workers. The reduction in the thorax weight was proportional to the decrease in the comb cell width, and this part of the body proved to be most susceptible to weight reduction caused by the use of small-cell combs. The rearing of workers in small-cell combs in the colony kept on standard-cell combs resulted in an increase in the value of the fill factor (thorax width to cell width ratio). The relatively constant body size of workers in combination with the use of small-cell combs resulting in an increase in the fill factor may be one of the determinants of increased resistance of the insects to Varroa destructor . The values of the morphometric traits commonly used for identification of honeybee subspecies, i.e., the length of the fore wing, the sum of the widths of 3rd and 4th th tergites, and the proboscis length, were inconsiderably altered vs. the changes in the comb cell width, which confirms their high suitability for identification of honeybee subspecies.
... Nevertheless, the impact of the comb cell width on the traits of bees and bee colonies has been poorly explored so far. The scientific interest in small-cell combs began only in the 21st century after the publication of reports showing that rearing brood in small-cell combs versus standard-cell combs limits the growth of populations of the common bee parasite V. destructor [27][28][29][30][31][32][33][34]. In Europe, the width of small cells on the wax foundation is 4.90 mm [26][27][28]. ...
... Nevertheless, a significant effect of the use of small-cell combs on the morphological traits of worker bees and bee colony biology was found. It consisted of a decrease in the thorax weight, head width and height, thorax width and length, width and length of fore wings, and width of the third and fourth tergites [26,[34][35][36]. Researchers additionally reported a longer lifespan of workers reared in colonies kept on small cell combs [37] and the contribution of small-cell combs to the higher effectiveness of bees' hygienic behavior [38]. ...
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This study is a continuation of the innovative research of the impact of rearing of bee colonies simultaneously on standard- and small-cell combs on the traits of worker bees and bee colonies. Its aim was to compare the activities of proteases and their inhibitors in the hemolymph of workers reared in a small-cell comb (SMC) and a standard-cell comb (STC) in colonies kept simultaneously on standard- and small-cell combs. The width of comb cells in which workers are reared has a significant effect on the protein concentration and the proteolytic system in the hemolymph, which is reflected in the activities of proteases and their inhibitors. The protein concentrations in the 1-day-old workers were always higher (p ≤ 0.05) in the SMC than STC workers. The opposite was found in the older bee workers (aged 7, 14 and 21 d). The activities of proteases and their inhibitors in the 1-day-old workers were always higher (usually significantly at p ≤ 0.05) in STC than SMC workers, and opposite results were observed in the groups of the older workers (aged 7, 14 and 21 d). The differences between the workers from small-cell combs and those reared in standard-cell combs may be related to their different tasks. Workers reared in small-cell combs probably work as foragers outside the nest, whereas bees reared in standard-cell combs work in the nest. This hypothesis requires confirmation. To reduce the impact of accidental determinants on the results of single-season research on honeybees, it is advisable that such investigations should be conducted for several consecutive years.
... Mechanical control: An early concept in reducing varroa reproductive potential was the idea that a 'small cell' restricts the physical space available to varroa to move and feed on developing bees, and that providing bees with frames imprinted with small cell patterning could impede varroa population growth. This intuitively appealing idea ultimately proved ineffective (Berry et al., 2010;Ellis et al., 2009;Seeley and Griffin, 2011). ...
Article
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Demand for better control of certain parasites in managed western honey bees (Apis mellifera L.) remains apparent amongst beekeepers in both Europe and North America, and is of widespread public, scientific, and agricultural concern. Academically, interest from numerous fields including veterinary sciences has led to many exemplary reviews of the parasites of honey bees and the treatment options available. However, summaries of current research frontiers in treating both novel and long-known parasites of managed honey bees are lacking. This review complements the currently comprehensive body of literature summarizing the effectiveness of parasite control in managed honey bees by outlining where significant gaps in development, implementation, and uptake lie, including integration into IPM frameworks and separation of cultural, biological, and chemical controls. In particular, I distinguish where challenges in identifying appropriate controls exist in the lab compared to where we encounter hurdles in technology transfer due to regulatory, economic, or cultural contexts. I overview how exciting frontiers in honey bee parasite control research are clearly demonstrated by the abundance of recent publications on novel control approaches, but also caution that temperance must be levied on the applied end of the research engine in believing that what can be achieved in a laboratory research environment can be quickly and effectively marketed for deployment in the field.
... This suggests that beekeepers should remove older comb or only use it for honey supers to reduce mite invasion. Interestingly, small cell comb, which was once suggested as a possible mechanical management system to reduce Varroa populations Kryger 2002, McMullan andBrown 2006), has now been deemed ineffective in reducing Varroa loads compared to normal comb (Seeley and Griffin 2011) and can actually elicit a higher chance of cell invasion. Thus, small cell comb should be discontinued as a mite treatment option (Berry et al. 2010, Coffey et al. 2010). ...
Article
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Varroa destructor (Mesostigmata: Varroidae) is arguably the most damaging parasitic mite that attacks honey bees worldwide. Since its initial host switch from the Asian honey bee (Apis cerana) (Hymenoptera: Apidae) to the Western honey bee (Apis mellifera) (Hymenoptera: Apidae), Varroa has become a widely successful invasive species, attacking honey bees on almost every continent where apiculture is practiced. Two haplotypes of V. destructor (Japanese and Korean) parasitize A. mellifera, both of which vector various honey bee-associated viruses. As the population of Varroa grows within a colony in the spring and summer, so do the levels of viral infections. Not surprisingly, high Varroa parasitization impacts bees at the individual level, causing bees to exhibit lower weight, decreased learning capacity, and shorter lifespan. High levels of Varroa infestation can lead to colony-wide varroosis and eventually colony death, especially when no control measures are taken against the mites. Varroa has become a successful parasite of A. mellifera because of its ability to reproduce within both drone cells and worker cells, which allows populations to expand rapidly. Varroa uses several chemical cues to complete its life cycle, many of which remain understudied and should be further explored. Given the growing reports of pesticide resistance by Varroa in several countries, a better understanding of the mite's basic biology is needed to find alternative pest management strategies. This review focuses on the genetics, behavior, and chemical ecology of V. destructor within A. mellifera colonies, and points to areas of research that should be exploited to better control this pervasive honey bee enemy.
... Also, it was once noted that small cell foundation resulted in shorter developmental times of honey bee pupae, interfering with Varroa reproduction because adult bees would emerge before the mites reached maturity (Camazine 1986). However, the reduced cell size had no measurable impact on mite population growth in several studies (Taylor et al. 2008, Ellis et al. 2009a, Berry et al. 2010, Coffey et al. 2010, Seeley and Griffin 2011. ...
Article
Full-text available
Varroa destructor is among the greatest biological threats to western honey bee (Apis mellifera L.) health worldwide. Beekeepers routinely use chemical treatments to control this parasite, though overuse and mismanagement of these treatments have led to widespread resistance in Varroa populations. Integrated Pest Management (IPM) is an ecologically based, sustainable approach to pest management that relies on a combination of control tactics that minimize environmental impacts. Herein, we provide an in-depth review of the components of IPM in a Varroa control context. These include determining economic thresholds for the mite, identification of and monitoring for Varroa, prevention strategies, and risk conscious treatments. Furthermore, we provide a detailed review of cultural, mechanical, biological, and chemical control strategies, both longstanding and emerging, used against Varroa globally. For each control type, we describe all available treatments, their efficacies against Varroa as described in the primary scientific literature, and the obstacles to their adoption. Unfortunately, reliable IPM protocols do not exist for Varroa due to the complex biology of the mite and strong reliance on chemical control by beekeepers. To encourage beekeeper adoption, a successful IPM approach to Varroa control in managed colonies must be an improvement over conventional control methods and include cost-effective treatments that can be employed readily by beekeepers. It is our intention to provide the most thorough review of Varroa control options available, ultimately framing our discussion within the context of IPM. We hope this article is a call-to-arms against the most damaging pest managed honey bee colonies face worldwide.
... Martin & Kryger [114] found evidence in support of this hypothesis when they compared the number of offspring per cycle of Varroa in brood of A. m. scutellata with that in brood of the larger A. m. capensis bees in A. m. scutellata cells. Seeley and Griffin [115] compared bees of the same origin that were either placed on frames with small (4,8 mm) or large (5,4 mm) cells. They measured population development of Varroa once a month-from mid-June to mid-October and did not find differences in population growth of the mites. ...
Article
Full-text available
We examine evidence for natural selection resulting in Apis mellifera becoming tolerant or resistant to Varroa mites in different bee populations. We discuss traits implicated in Varroa resistance and how they can be measured. We show that some of the measurements used are ambiguous, as they measure a combination of traits. In addition to behavioural traits, such as removal of infested pupae, grooming to remove mites from bees or larval odours, small colony size, frequent swarming, and smaller brood cell size may also help to reduce reproductive rates of Varroa. Finally, bees may be tolerant of high Varroa infections when they are resistant or tolerant to viruses implicated in colony collapse. We provide evidence that honeybees are an extremely outbreeding species. Mating structure is important for how natural selection operates. Evidence for successful natural selection of resistance traits against Varroa comes from South Africa and from Africanized honeybees in South America. Initially, Varroa was present in high densities and killed about 30% of the colonies, but soon after its spread, numbers per hive decreased and colonies survived without treatment. This shows that natural selection can result in resistance in large panmictic populations when a large proportion of the population survives the initial Varroa invasion. Natural selection in Europe and North America has not resulted in large-scale resistance. Upon arrival of Varroa, the frequency of traits to counter mites and associated viruses in European honey bees was low. This forced beekeepers to protect bees by chemical treatment, hampering natural selection. In a Swedish experiment on natural selection in an isolated mating population, only 7% of the colonies survived, resulting in strong inbreeding. Other experiments with untreated, surviving colonies failed because outbreeding counteracted the effects of selection. If loss of genetic variation is prevented, colony level selection in closed mating populations can proceed more easily, as natural selection is not counteracted by the dispersal of resistance genes. In large panmictic populations, selective breeding can be used to increase the level of resistance to a threshold level at which natural selection can be expected to take over.
Article
The parasitic mite Varroa destructor (Acari: Varroidae) is a major cause of overwintering honey bee (Apis mellifera) colony losses in the United States, suggesting that beekeepers must control Varroa populations to maintain viable colonies. Beekeepers have access to several chemical varroacides and nonchemical practices to control Varroa populations. However, no studies have examined large-scale patterns in Varroa control methods in the United States. Here we used responses from 4 yr of annual surveys of beekeepers representing all regions and operation sizes across the United States to investigate use of Varroa control methods and winter colony losses associated with use of different methods. We focused on seven varroacide products (amitraz, coumaphos, fluvalinate, hop oil, oxalic acid, formic acid, and thymol) and six nonchemical practices (drone brood removal, small-cell comb, screened bottom boards, powdered sugar, mite-resistant bees, and splitting colonies) suggested to aid in Varroa control. We found that nearly all large-scale beekeepers used at least one varroacide, whereas small-scale beekeepers were more likely to use only nonchemical practices or not use any Varroa control. Use of varroacides was consistently associated with the lowest winter losses, with amitraz being associated with lower losses than any other varroacide product. Among nonchemical practices, splitting colonies was associated with the lowest winter losses, although losses associated with sole use of nonchemical practices were high overall. Our results suggest potential control methods that are effective or preferred by beekeepers and should therefore inform experiments that directly test the efficacy of different control methods. This will allow beekeepers to incorporate Varroa control methods into management plans that improve the overwintering success of their colonies.
Chapter
L’alveare offre un habitat favorevole a un’ampia varietà di organismi, alcuni dei quali molto pericolosi. Le malattie sono causate da organismi che trovano nell’ape un ospite adatto in cui svolgere il proprio ciclo vitale. Molti di questi sono parassiti specifici obbligati, cioè la loro esistenza è indissolubilmente legata all’ape, che trovano nell’alveare rifugio, fonte di cibo e regolazione termica e igrometrica garantita costantemente dalle api. Inoltre, l’ape offre un’efficace sistema di trasmissione che permette ai parassiti di invadere nuove colonie per via orizzontale, attraverso la deriva o il saccheggio, e per via verticale, mediante la sciamatura. Tali organismi possono essere distinti in microparassiti es. virus, batteri, microsporidi), spesso indicati come patogeni, e in macroparassiti, come nel caso degli acari.
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The varroa mite (Varroa destructor) is an ectoparasite of the western honeybee Apis mellifera that reproduces in the brood cells. The mite will generally kill colonies unless treatment is given, and this almost universally involves the use of chemicals. This study was undertaken to examine the effect of small cell size on the reproductive success of the mite, as a method of non-chemical control in the Northern European honeybee Apis mellifera mellifera. Test colonies with alternating small and standard cell size brood combs were sampled over a three-month period and the population biology of the mites evaluated. To ensure high varroa infestation levels, all colonies were infested with mites from a host colony prior to commencement. A total of 2229 sealed cells were opened and the varroa mite families recorded. While small-sized cells were more likely to be infested than the standard cells, mite intensity and abundance were similar in both cell sizes. Consequently, there is no evidence that small-cell foundation would help to contain the growth of the mite population in honeybee colonies and hence its use as a control method would not be proposed.
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The aim of this study was to investigate an underlying mechanism of the apparent tolerance of Africanized honey bees (AHB) to Varroa jacobsoni mites in Mexico. This was achieved by conducting the first detailed study into the mites' reproductive biology in AHB worker cells. The data was then compared directly with a similar study previously carried out on European honey bees (EHB) in the UK. A total of 1071 singly infested AHB worker cells were analyzed and compared with the data from 908 singly infested EHB worker cells. There was no significant difference between the number of mother mites dying in the cells (AHB = 2.0%, EHB = 1.8%); the mean number of eggs laid per mite (AHB = 4.86, EHB = 4.93); the number of mites producing no offspring (AHB = 12%, EHB = 9%); and developmental times of the offspring in worker cells of AHB and EHB. However, there was a major difference between the percentage of mother mites producing viable adult female offspring (AHB = 40%, EHB = 75%). This was caused by the increased rate of mite offspring mortality suffered by the first (male) and second (female) offspring in AHB worker cells. Therefore, only an average of 0.7 viable adult female offspring are produced per mite in AHB, compared to 1.0 in EHB.
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The ability of Varroa destructor to reproduce in the African honey bee Apis mellifera scutellata was studied. In addition, the effects of space within the brood cell and short brood developmental time on mite reproduction, was investigated using A. m. scutellata cells parasitised by a A. m. capensis worker pseudo-clone. In A. m. scutellata worker cells Varroa produced 0.9 fertilised females per mother mite which is the same as found in susceptible European honey bees, but greater than the 0.4 produced in cells containing the pseudo-clone. Low mite reproductive success in cells containing pseudo-clone was mainly as a result of increased mite mortality. This was caused by male protonymphs and some mothers becoming trapped in the upper part of the cell due to the pseudo-clone being 8% larger than their host and not due to their short developmental time. Therefore, mite populations in South African A. m. scutellata and A. m. capensis honey bees are expected to increase to levels observed in Europe and USA.
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Until the late 1800s honeybees in Britain and Ireland were raised in brood cells of circa 5.0 mm width. By the 1920s this had increased to circa 5.5 mm. We undertook this study to find out if present-day honeybees could revert to the cell-size of the 1800s and to evaluate resulting changes in honeybee morphometry. Seven measurements were made; head width, radial cell length, trachea diameter, cubital index, discoidal shift, bee mass and abdominal markings. The study showed that the colonies of Apis mellifera mellifera bees had no apparent difficulty in drawing out the wax and raising brood in the reduced brood cells. Bees reared in these cells were significantly smaller, but this reduction was not in proportion ($<$20%) to the change in the brood-cell size in contrast to the strongly proportional relationship in other bee strains. Also the ratio of thorax width to cell width (fill factor') was much larger in the Apis mellifera mellifera strain.
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In three independently replicated field studies, we compared biometrics of Varroa mite and honey bee populations in bee colonies housed on one of two brood cell types: small-cell (4.9$\pm$0.08 mm cell width, walls inclusive) or conventional-cell (5.3$\pm$0.04). In one of the studies, ending colony bee population was significantly higher in small-cell colonies (14994$\pm$2494 bees) than conventional-cell 5653$\pm$1082). However, small-cell colonies were significantly higher for mite population in brood (359.7$\pm$87.4 vs. 134.5$\pm$38.7), percentage of mite population in brood (49.4$\pm$7.1 vs. 26.8$\pm$ 6.7), and mites per 100 adult bees (5.1$\pm$0.9 vs. 3.3$\pm$0.5). With the three remaining ending Varroa population metrics, mean trends for small-cell were unfavorable. We conclude that small-cell comb technology does not impede Varroa population growth.
Article
The effect of honey bee (Apis mellifera) worker brood cell size on cell infestation and reproductive success of Varroa destructor in New Zealand was determined by establishing ten nucleus colonies with mosaic frames, each consisting of cells drawn from five different foundation sizes. When the brood were 18–20 days old, 1636 cells were individually uncapped and the number of adult and deutonymph female mites were recorded. The internal width of each brood cell was also measured. The data were analysed according to the imprint size of the “foundation” specified by the supplier, and the “measured” internal width of each individual drawn brood cell. The “foundation” cell size had no significant effect on the reproductive success of V. destructor, but the proportion of cells that were infested by adult female mites was significantly different. A significantly higher proportion of the cells drawn from the 4.8 mm imprint “foundation” were infested compared to those of the other sizes.“Measured” brood cell size had no significant effect on mite reproduction or infestation.
Article
Varroa jacobsoni reproduces in honey bee brood cells. Here the behavioral activity and use of space by infestingVarroa females and progeny were quantified in transparent artificial brood cells. The time-activity budget of both infesting and developing mites converged toward a stable pattern which was established during the bee prepupal stage of the infesting mites and the protonymphal stage of mite progeny. The pattern was such that infesting females and offspring eventually divided their activity between the fecal accumulation on the cell wall, which served as the rendezvous site for newly molted individuals, and the feeding site prepared on the pupa by the foundress. Other parts of the cell wall were used for oviposition and molting, away from the fecal accumulation on which activity of mobile stages was concentrated. Space structuring and the time-activity budget inVarroa probably evolved to enhance the number of fertilized females produced within the capped brood, where space and time are limiting factors. These behavioral adaptations parallel those of other mite species which show group behavior within cavities.
Article
Due to a continuing shift toward reducing/minimizing the use of chemicals in honey bee colonies, we explored the possibility of using small cell foundation as a varroa control. Based on the number of anecdotal reports supporting small cell as an efficacious varroa control tool, we hypothesized that bee colonies housed on combs constructed on small cell foundation would have lower varroa populations and higher adult bee populations and more cm(2) brood. To summarize our results, we found that the use of small cell foundation did not significantly affect cm(2) total brood, total mites per colony, mites per brood cell, or mites per adult bee, but did affect adult bee population for two sampling months. Varroa levels were similar in all colonies throughout the study. We found no evidence that small cell foundation was beneficial with regard to varroa control under the tested conditions in Florida.