Widerlegung der wissenschaftlichen Studien über die Uneffektifität der kleinen Zellen

Warum kamen die wissenschaftlichen Untersuchungen über den Einfluß der kleinen Zellen auf die Varroamilben zu negativen Ergebnissen? (Erik Österlund)

• Es gibt zwei frühe Untersuchungen, die den Einfluss der kleinen Zellen auf die Varroamilben studierten. Beide wurden in Brasilien unter Bedigungen unternommen, die sich von denen, die in Europa, USA und Neuseeland  gemacht wurden, unterscheiden. Die ersten zeigten einen bedeutsamen Vorteil der kleinen Zellen.
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• Die späteren Tests konnten die Ergebnisse der ersten wissenschaftlichen Studien aus Brasilien nicht bestätigen.
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• Da diese späteren Tests nicht die ersten beiden bestätigten, wäre es wohl die normale Reaktion gewesen, herauszufinden, was die ersten beiden Studien gemein hatten und wo die Unterschiede zwischen den positiven und den negativen bestanden. Ich konnte aber nichts desgleichen finden. Warum aber nicht? Es ist ein gängige wissenschaftliche Gewohnheit derat vorzugehen. Ich will nun genau dies hier versuchen.

• Unterschiede zwischen den ersten Versuchen in Brasilien und den später ausgeführten
  

1. Die Versuche wurden in Südamerika gemacht
2. Die verwendeten Bienen waren afrikanisierte Bienen
3. Die Bienen der ersten Versuche waren Varroaresistent
4. Die Bienen der erstenVersuche lebten üblicherweise auf kleinen Zellen (SC)
5. Keine oder nur wenige großzellige Bienen (LC) waren in der Nachbarschaft
6. Die Bienen wurden nie oder nur wenig mit Chemikalien behandelt.
7. Das Wachs der Bienenwaben war frei von chemischen Rückständen
8. Epigenetische Unterschiede durch die erwähnten Unterschiede der Umgebung

• zusätzliche Unterschiede zu den 8 oben aufgeführten

1. Verhinderung von Verflug und Räuberei
2. Wachs frei von chemischen Rückständen
3. Was wurde gefüttert wenn gefüttert wurde

• Überlebensfähigkeit
  In den meisten Studien über Varroaresistenz, auch in denen wo es um Zellgrößen ging, wurde das Augenmerk auf Reproduktionsrate und Bevölkerungszuwachs der Varroamilben gelegt. Das was für einen praktischen Imker zählt sind aber das Überleben der Bienenvölker und gute Honigproduktion. Auf jeden Fall ist eine der wichtigsten Eigenschaften zur Bekämpfung der Milbe das sogenannte  VSH (Varroa Sensitive Hygiene) (Ref 13,14), das Aufspühren von Milben in der verdeckelten Brut, vor allem solche mit Nachwuchs, das Öffnen dieser Zellen, das oft gefolgt wird vom Ausräumen der infizierten Bienenpuppe. Dieses wichtige Merkmal ist nichts neues. Auch wenn die Vermehrungsrate der Varroen langsam ist, werden sie anwachsen, nur etwas langsamer. Schlussendlich wird die Milbenpopulation für die Bienen zu hoch sein und sie müssen aktiv etwas tun um zu überleben, indem sie sie direkt bekämpfen. Und sie müssen bereits beginnen, wenn der Milbenpopulation noch gering ist.

• Test von Hans-Otto Johnsen nach ein paar Saisonen. Er wurde mit Bienen durchgeführt, die nicht auf Varroaresistenz ausgewählt wurden. Siehe seinen online Artikel (Ref 20).Testergebnis: kleinzellige Bienen bringen mehr Honig – die Varroapopulation ist in kleinzelligen Stöcken deutlich geringer.
• In den 60er Jahren testete der Besitzer eines der größten Imkerzubehörgeschäfte Schwedens,  Evert Svensson, der ebenfalls Profiimker ist, größere Zellen als seine bis dahin verwendeten 5.1-5.2 mm. Er verwendete die größeren Zellen in ungefähr 50 Bienenstöcken, an einem Bienenstand über einige Jahre hinweg. Seine Schlussfolgerung war, dass größere Zellen weniger Geld in der Tasche gaben.

hier die gesamte Studie von Erik Österlund:

ERIK ÖSTERLUND

Smaller cells in the broodnest than what is most common today, does it have any advantages? Particularly – does it have any advantages concerning Varroa resistance for the bee colony? Bees naturally build different sizes of cells depending on where they are built in the nest, smallest downward nearest the entrance where the brood is and biggest upwards and away from the entrance where honey is stored.

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When wax foundation first was made in a commercial scale, beginning with A. I. Root in USA in 1876, natural comb evidently was measured and an average became the guideline to choose the easily manageable size 5 cells to the inch (Ref 1), which is 5.08 mm per cell including one cell wall. This is easiest measured over the parallel sides taking 10 cells at a time and divide by 10. The actual average was said to be somewhat bigger. This meant that in the broodnest the average was still smaller – remember, the average. And the average for honey storage cell sizes were of course bigger.

Two early works investigating small cells influence on Varroa mites. Both done in Brazil under circumstances differing from those made in Europe, USA and New Zealand. They showed a significant advantage of small cells.

Already in 1888 Frank Cheshire in England wrote in his Bees and Beekeeping, Vol II2 (Ref 2): “The idea that it is desirable to increase the dimension of our bees … I have ventured, more than once to stand alone in condemning it….” This enlargement was achieved by increasing the size of the cells.

A century later

100 years later it was rediscovered by Dee and Ed Lusby that bees naturally build different cell sizes. Bee Culture was among the first to publish works on small cell size in 1990, Erickson et al, On the size of cells. Soon there were articles and papers published supporting the idea that smaller cell sizes contributed to varroa resistance, by Erickson (Ref 3), Lusbys(Ref 4), Message&Goncalves (Ref 5) and Piccirillo&DeJong (Ref 6). Also anecdotal reports in forums etc appeared. And many began testing small cells (SC). Small cells are 4.8-5.1 mm. Mostly mentioned is 4.9 mm. Commercial foundation varied between 5.3-5.7 mm in their cell size.

Later tests did not verify the first research papers from Brazil. It seemed to become common among researchers to dismiss the first positive results as associated with Africanized bees. Especially those whose own tests didn’t show any advantages for SC. In 2008 and 2009 there were some tests published that have been used to make a “final” statement that “the case is closed” concerning difference in influence on varroa resistance from small (SC) or large (LC) cells.

If there had been only one positive test showing SC had positive influence on Varroa resistance it wouldn’t had been strange to dismiss it in the light of later tests. It’s often said that one time is no time in re- search context. But the first paper by Message & Goncalves in Apidolo- gie 1995 was verified by Piccirillo & De Jong in Genetics and Molecular Research in 2003, even if it wasn’t a true replication test.

The natural response to later tests that did not verify these two papers would have been to investigate what was in common between the two positive papers and what differed between the positive and the not positive ones. But no such investigation has been able to be found. Why not? It is a natural scientific response to do so. I will try to do this here.

 

Important differences

In the context of scientific research these differences may be crucial and should not be taken lightly. They could be the explanation for the differing results and should be taken in account for new research before the conclusion ”case is closed” could be made.

It must be of uttermost interest to investigate the differences in test context for theses positive tests and tests not being positive. Note that there are no tests showing it’s negative to use SC!

1. Could the results be dismissed because these tests were made in South America?
No, climate may influence, but no research verifies any hypothesis that all bees in the tropics are resistant to the Varroa mite. Not resistant bees are kept in similar climate.

2. Could the results be dismissed because the bees in these tests were Africanized?
No, There is no research showing any such differences between African and European honeybees. On the contrary these types of bees are both Apis Mellifera, closely related and interbreed easily.

3. Bees in other tests have not been resistant to Varroa. This is an interesting difference. Today there are reports of quite some beekeepers in different places not treating at all for Varroa mites and bees seem to tolerate the presence of mites and still produce normally. There are SC and other bees among those. There are tests showing most probable reasons for the resistance are changes in the behaviour of the bees. Could these changes in behaviour in some way have effects on the bees’ relation to an SC environment?

4. When bees are born in SC they may well have been fed differently. And bees born in SC may well be feeding larvae differently. Differences in feeding behavior have been shown in SC-colonies. Different feeding has influence on the phenotype of bees. How big behaviour differences are resulting? In the Brazil tests the nurse bees have been born in SC and fed by SC-bees. In most of the other tests the nurse bees have been born in LC and fed by LC bees.

5. There is a growing awareness of the influence of the exchange of bees between bee colonies. It can be quite big under certain circumstances. Two of the causes are drifting and robbing. Robbing can be slow, almost not noticeable, and it can be intensive. This exchange of bees can be destructive for the possibilities to get an accurate test result. Even 1.5 km can be too short distance to avoid significant not wanted influence. (Ref 7)

6. When bees are treated with something that kills parasites or microbes, they are loosing also beneficial microbes. This can influence their immune system and their behavior. In the short perspective of course it’s understandable if a beekeeper chooses to save his bees from dying.

7. Wax in combs has been found to contain a substantial amount of different chemical residues from varroa treatments, AFB treatments and plant protection sprays. That of course applies for such environments where such a result is possible, which applies for many areas in North America and Europe. Chemicals in sublethal doses are known to influence immune system and bee behavior in a negative way.

8. Heritable changes take place in the genom of all living beings, also bees, depending on changes in the environment. It’s been more and more discussed among genetics. It’s called epigenetics as the changes is not taking place in the composition of the DNA in the chromosomes, but in how the genes and even fractions of genes are expressed, “turning them on’ or ‘turning them off’. This effects the production of proteins and thus the phenotype of the bee. (Ref 8)

Epigenetics

Epigenetic adjustments are inheritable to the next generations and when environment changes again there will be new epigenetic changes. This is a powerful way for animals and plants to adapt to new environments. Actually there is no other way to explain the formation of resistant Apis mellifera bees in South America in the 1980s and in South Africa in the 2000s. In both cases it took about 5 years for Apis mellifera bees to develop resistance, and without masses of bees dying from the Varroa mites. What was seen was a decrease of a 50 % mite infestation (one mite on every second bee) to about 5 % mite infestation (one mite on every 20th bee). And this was achieved with the conditions described in paragraphs 2, 4, 5, 6 and 7.

Changes in the Histone Code and DNA-methy- lation are made due to changes in the envi- ronment which causes changes in the produc- tion of proteins. These are two epigentic pro- cesses. The changes are inherited, until the environment changes again.

 

Not the natural host

The paragraph describing a difference of the composition of the bee itself with European bees are no 2 of course, the somewhat different genetics. Most prominent difference was probably the more varied genom. But remember the African bee is not the natural host of Varroa mites either.

A prominent difference of African bees compared to European is probably a bigger genetic variation contributing to the adaptation process. But the 5 years are way to short to give time for genetic selection after recombination of nucleus DNA to form a resistant bee. The only powerful process (rather processes) that can explain such a short successful adaptation is epigentics.

These epigentically changes in the Brasilian bee adapted to small cells and later also changed into resistance may well have contributed to the different reactions to small and large cells compared to the European bees used in the other tests.

Epigenetics actually explains more than quick build up of Varroa resistance. All kind of adaptations to new environ- ments that takes place we understand depend on epigenetic processes. Next step (or at the same time) is the genetic changes taking place th- rough selection.

Early studies with different cellsizes in the same colony

Some early studies designed in a similar way as those of Message&Goncalves (1995) and Piccirillo&DeJong (2003) are one by Davidson&Fries (1992) (Ref 10) in Sweden and another by Taylor&Goodwin (2001) in New Zealand (Ref 11). The later one was reorganized and republished by Taylor, Goodwin, McBrydie & Cox (2008)(Ref 12). This later publication was one of the publications of three referred to as ‘closing the case’ of SC (small cell) compared to LC (large cell).

Two works investigating small cells eventual effects on Varroa mite reproduction in a similar fashion as those in Brazil, but made under quite differing circumstances that well may have influenced the results.

Both Davidson & Fries and Taylor & Goodwin have all the 8 differences described above compared to Message & Goncalves and Piccirillo&deJong.  Also, their LC bees had difficulties drawing SC foundation evenly following the SC imprints. And Davidsson didn’t test 4.9 mm as SC but rather 5.1 mm (900 cells/sq dm).

Their tests were performed with bees that probably were not adapted, that is epigentically changed, in a maximum way to the altered environment that the presence of the Varroa mite resulted in. Varroa was detected on the island Gotland in the Baltic 1987 and in southern Sweden 1991. The mite was detected 2000 in New Zealand.

Adaptation time

The adaptation process to resistance to the mite took about 5 years in South America and South Africa. After about the same number of years with big Varroa populations in the colonies, many beekeepers in Sweden reported a noticeable drop in size of the seasonal population peaks of the mite. In some cases where the beekeepers are quite isolated from bees of other beekeepers and use more resistant bees, they don’t use any treatment help for the bees to deal with the mite.

To start the VSH-trait, the number of mites probably will have to reach some density level to trigger the bees to chase them. This threshold needs to be small enough to keep the mite population enough small throughout the season, even if some reinvasion occurs.

 

Differences explained

9. One thing that is seldom talked about in design of tests, is which precautions were taken to avoid drifting and robbing during registering the data for all the figures in tables and graphs! I know through experience (when nectar flow is low) that if these kind of thorough lifting up of combs and measures taken in a yard is done continuously during even less than half an hour, it doesn’t take long before you have a robbing going on, which makes any measures of figures more or less worthless. And once the bees have learned to rob, the next day (if nectar flow is low) the bees develop a robbing mode even quicker.

10. We don’t know anything about the chemical residues in the wax combs used. Recent tests of wax in combs have shown alarmingly high residue levels from miticides and agricides in brood nest combs. We know too little about the effects of this on the immune system (RNAi, peptides, hemocytes, microbe-balance, etc.) and defense system (defense behavior like VSH, grooming, cleaning out virus filled bees from the hive) in the bee colony. We do know that a test made by Randy Oliver with HSC (fully drawn plastic small cell combs)(Ref 15), which have no such residues, gave a much slower varroa buildup than on large cell size (drawn on plastic foundation).

11. When a drought is at hand, nectar availability is often scarce. To help the bees they might be fed. We don’t know from the description

Robbing inferno at data collection in a Varroa test.

of the tests what is fed and how much. Is it honey, high fructose corn syrup (HFCS) (Ref16,17) or sucrose solution fed? Are proteins low in colonies and therefore pollen or pollen substitutes supplied? We know that there is a discussion concerning the nutrition value, or rather lack of, in HFCS. What you feed can influence the performance and behavior of your bees. This could be part of the explanation why the ending bee populations in some tests were remarkably low in my view.

The three ‘case is closed-papers’ (CCP)

In the November issue of Bee Culture 2009 there was an article by Jennifer Berry (Ref 18), with the message that there is no value in small cell size as a tool against Varroa mites. The article covers three investigations of small cell effect on varroa population build up during a short period of time, half a year to a year. The article ends with a clear message that her article is the final word concerning small cells against Varroa and ends with words she thinks applies:

“…the so-called enlightenment of the 17th and 18th centuries engendered investigative methods that mitigate against bias and presupposition. From this point on, arm-chair science was doomed, and many a brilliant idea has since been shipwrecked by the unforgiving objectivity of the scientific method.”

The conditions listed in paragraphes 3-8 above describe differences compared to those in these three CCP-tests. Actually most small cell tests, at least outside South America are differing the same way.

CCP1: New Zealand test

One of the papers mentioned in the Berry BC-article is the Taylor & Goodwin-paper. And the result, similar to that of Davidsson&Fries, arrives at no advantage for small cells. As has been already mentioned there are at least 8 conditions that differ from the tests done in Brazil. The Brazilian tests are showing positive influences for small cells concerning varroa reproduction. (Survivability is though not investigated in any of these tests.)

Alternative test design:

The results of the NZ and Davidsson tests, creates the need for finding out if these differing conditions compared to the Brazilian, have significance for the differing results. To find out that we need a test which use 2 apiaries separated by a distance of about 3 km. One apiary having only bees adapted since maybe 5 years on small cells supplied with pieces of combs according to the test set up. With no LC bees within 3 km. The other test apiary having only LC bees set up the same way. The queens must likewise belong to a stock of adapted SC and LC bees respectively. To overcome the disadvantage of differing genetics in the two apiaries the number of hives in each apiary should be more. Maybe 2-3 of each and no sisters. Residue free wax for the foundation in the combs should be used (or plastic foundation). High fructose corn syrup or pollen substitutes should not be used if feeding is necessary.

CCP2: Berry test

The second CCP-paper is one of her own, Berry, Owens & Delaplane, Apidologie (2009)(Ref19). She began the test with bees from a beekeeper successfully keeping bees on 4.9 mm cell size without using treatments. That is note-worthy. But she mixed them with LC-bees and made packages. She kept the test (SC) and control colonies (LC) in the same yard. The resulting mite populations were too small to show any differences in ending mite population sizes. Compare with the first year result presented in a small cell size test by Prof Fries in Sweden (se graph).

Her goal was though not to measure ending mite population sizes but reproduction rate, which she meant was enough with the short time used. For this decision she leaned on only one paper saying a duration

The number of failing colonies in her test is striking. How come? The first batch of 10 + 10 colonies set up in August 2006 should have been enough. But already in October there were only 3 + 4 left. Something went wrong, maybe with the introduction of the queens. So another 10 + 10 colonies were started in March 2007. In June 2007 these two batches were ended. Why not let them continue? Next April in 2008 a third batch of 10 + 10 colonies was set up and run till August 2008. And these are called three separate tests, but done the same way. All figures were pooled except the end populations of bees. Why? The tests were not done the same way. The first one lasted six months. The second began with foundation instead of drawn combs and lasted three months. The third began with drawn comb like the first and lasted four months. Were they replicates of each other?

Alternative test design:

She had a great opportunity to use a stock adapted to small cells and as well resistant to varroa mites (no treatments were used on those bees). But she missed it. Instead of pooling SC and LC bees, two separate apiaries should have been set up, one with SC and one with LC bees, 3 km apart, with no other bees in the neighborhood. To overcome the disadvantage of having a separate apiary for the control colonies, the number of colonies in both groups should be increased. Even better had been to set up 2 apiaries for each group, totaling 4 apiaries. Residue free wax for comb foundation or plastic foundation should have been used. And no HFCS or pollen substitutes for feeding, but real honey or sucrose solution and real pollen. Also the test period should be long enough to enable the mite population to grow over the ”normal” amount of mites for varroa resistant bees (Ref 21), which it probably would after a couple of seasons in the LC apiary.

 

But Johnsen knew that robbing, slow or intense, is easily aroused if you keep your hives open long enough, which is not long at all during nectar drought. Therefore he worked the hives late in the day close to dusk. And he worked the hives quickly and had entrances restricted in size. And when harvesting he kept the combs and boxes harvested closed from bees. He didn’t feed the colonies but complement feeding for winter with sucrose solution. The wax in the combs was free of chemical residues.

We don’t know how data were collected by Ellis (Ref 2)&Hayes. 700 m is no hinder for robber bees, especially during a drought. If robbing is started, even only slightly and once, the test may well have been ruined, through mites being distributed and evened out mite populations with the help of robbers. I’ve myself seen a test yard roaring of robbers in the middle of the day while data collection was going on during a drought.

Sister queens were used to all colonies. Queens from SC- or LC-stock? Probably LC-stock. Their genom is not epigentically adapted to small cells. We don’t know how much that interfere with the result. To over- come that SC-queens could have used in SC-colonies and LC-queens in LC-colonies.

We don’t know what kind of feed that was used. HFCS is suspected of just keeping colonies alive but not making it possible for them to thrive and grow. Pollen substitutes should not be used more than a couple of brood cycles. The bees need real pollen for a lengthy protein feeding. Lack of protein may lead to lowered immune and defense system me- chanisms.

Ellis (Ref 2) & Hayes had a test period of one year. The ending total number of mites indicates that the test period was just about too short. It had reached 3600-4000 mites, lowest with the LC-bees. But the LC-colonies were only half the strength of SC-ones. About 7000 bees compared to 15000. According to the findings of Mondragón, Spivak and Vandame (2005)( Ref 23) the mite population in resistant bees (AHB) in Mexico varied during the season and averaged almost 4000 mites in the colony. This tells us the test should have been running for at least another season.

Notable is the low bee populations in all bee colonies. Are the apiary surroundings almost void of nectar sources? Were the bees fed HFCS instead of honey or sucrose solution? Is the wax in the combs loaded with chemical residues? The SC colonies were more than doubled in strength at the end of test year in May 2008 compared to one year earlier. The LC colonies are just slightly bigger than the starting size. Another season would have produced an interesting continuation.

There are in spite of not optimal design of the test some interesting trends that would have been interesting to follow another season. Maybe the benefit of small cells is to provide a bigger visible variation of varroa resistance making a better selection possible for breeding?

In May 2008 mites per adult bee was 35 % lower in SC-colonies (9 % and 14 % respectively). Mites per brood cell 23 % lower in SC-colonies (13 % and 17 % respectively).

Alternative design:

Establish 4 instead of 2 apiaries. Locate them 2-3 km apart. One SC- apiary and one LC-apiary with SC sister queens. (Queens bred from a queen in a SC colony. Her mother and grandmother have also been from SC colonies.) One SC-apiary and one LC-apiary have LC sister queens. Feed when needed in first place with honey and real pollen (best with pollen dust outside the hives protected from rain), if not possible with sucrose and pollen substitutes. The test period should be at least two years.

Other tests

The three CCP-tests are covered because of the extraordinary brave conclusion in the Bee Culture article by Jennifer Berry. I felt there was a need to challenge that conclusion. More papers on small cells have been published after the three CCP-ones. I will mention a few. One comes to the conclusion that small cells are beneficial for the bee colony in figh- ting the mite. Another that they are not. Both are focused on reproduction of the mites in first place as a result of how much fertile progeny the mites can produce. No consideration seems to be taken to eventual actions of the bees.

Relative frequency distribution of worker brood cells width (class intervalls) in which a mother mite was found. Cell size is inside measurement not including one cell wall. Graph made with data from the article of Maggi et al.

The first one is authored by Matías Maggi et al, published in Ex- perimental and Applied Acarology 2010 and entitled Brood cell size of Apis mellifera modifies the reproductive behaviour of Varroa destructor (Ref 24). The test is conducted in Argentina at the coast well south of Buenos Aires. One whole frame with capped worker brood was analyzed from 5 colonies. Every cell with mites was measured in size. They vary in size from much smaller than 4.9 mm to much bigger. The stock of bees was European. They hadn’t been treated with miticides for 18 months and the infestation in brood was in average 30 %. (Some info comes from personal communication.) One of the conclusions was: ‘We found that brood cell width in A. mellifera colonies affected the invasion and reproduction rate of V. destructor under natural conditions.’

The second is authored by T Seeley and S Griffin, published in Api- dologie 2011 and entitled Small-cell combs does not control Varroa mites in colonies of honeybees of European origin (Ref 25).  The test was done in New York State. Two apiaries with 7 colonies each were established from packages from 7 colonies highly infested by Varroa mites. They were placed 120 m apart in which the colonies were spaced 5 m apart. All this to avoid drifting. The colonies were established June 2, 2009, and ended in October the same year. All bees were LC-bees. All queens were LC-queens from the same commercial source. The SC-colonies got fully drawn plastic SC-combs. The LC colonies fully drawn LC wax combs. Colony strenght was always somewath smaller in SC-colonies.

References (Click on the url to reach the referenced article on internet)

1.The ABC and XYZ of Beekeeping, A. I. Root, 1910: http://archive.org/details/abcxyzofbeecultu00root –> p. 266, 267

2.Bees and Bee-Keeping, Frank Cheshire: http://GeneralBooksClub.com/book.cfm?id=48283090

3.Helping Honey Bees Fight Mites, Eric Erickson: http://www.ars.usda.gov/is/ar/archive/may97/honey.pdf

4.Beesource Ppoint of View, Ed & Dee Lusby: http://www.beesource.com/point-of-view/ed-dee-lusby/

5.Effect of the size of worker brood cells of Africanized honey bees on infestation and reproduction of the ectoparasitic mite Varroa jacobsoni Oud, D. Message, L.S. Gonçalves: http://www.researchgate.net/publication/41700870

6.The influence of brood comb cell size on the reproductive behavior of the ectoparasitic mite Varroa destructor in Africanized honey bee colonies, Giancarlo A. Piccirillo1, and D. De Jong: http://www.funpecrp.com.br/gmr/year2003/vol1-2/gmr0057_full_text.htm

7.Peter Rosenkrantz speaking in Hässleholm, Sweden, March 19, 2011. Video sequence from 50.16 minutes into the speach to 52.43: http://bambuser.com/v/1511682

8.New Components of Epigenetic ’Code’ for Honey Bee Development Discovered, Science News: http://www.sciencedaily.com/releases/2012/12/121211101942.htm

9.ANALYSIS OF VARROA DESTRUCTOR INFESTATION OF SOUTHERN AFRICAN HONEYBEE POPULATIONS, MIKE ALLSOP: http://upetd.up.ac.za/thesis/available/etd-08082007-153050/unrestricted/dissertation.pdf

10.The influence of cell size in Varroa reproduction, Davidsson, Mia: http://beeman.se/research/cell.htm

11.Can the reduction of Cellsize reduce the impact of Varroa, M.A Taylor and R.A. Goodwin: http://maxa.maf.govt.nz/sff/about-projects/search/00-256/cell-size-impact-on-varroa.pdfRearranged and republished:

12.The effect of honey bee worker brood cell size on Varroa destructor infestation and reproduction, Michelle A. Taylor, R. Mark Goodwin, Heather M. McBrydie and Harlan M. Cox: http://www.ibra.org.uk/articles/20081124_18

13.Varroa sensitive hygiene, Wikipedia: http://en.wikipedia.org/wiki/Varroa_sensitive_hygiene

14.Effect of Brood Type on Varroa-Sensitive Hygiene by Worker Honey Bees (Hymenoptera: Apidae), Jeffrey W. HArris: http://naldc.nal.usda.gov/download/21494/PDF

15.Trial of HoneySuperCell® Small Cell Combs, Randy Oliver:

http://scientificbeekeeping.com/trial-of-honeysupercell-small-cell-combs/

16.Formation of Hydroxymethylfurfural in Domestic High-Fructose Corn Syrup and Its Toxicity to the Honey Bee (Apis mellife- ra), BLAISE W. LEBLANC, GILLIAN EGGLESTON, DIANA SAMMATARO, CHARLES CORNETT, RENEE DUFAULT, THOMAS DEEBY, AND ELDWIN ST. CYR: http://www.uwplatt.edu/~cornettc/Ag%20and%20Food%20Publish.pdf

17.Preliminary Results on Bee Longevity – HFCS vs. Sucrose, D. Sammataro, M. Weiss, J. Finley: http://projectapism.org/content/view/66/27/

18.Small Cell Foundation And Varroa Mites, Jennifer Berry: http://www.beeculture.com/storycms/index.cfm?cat=Story&recordID=676

19.Small-cell comb foundation does not impede Varroa mite population growth in honey bee colonies, Jennifer A. Berry1, Wil- liam B. Owens2, Keith S. Delaplane: http://www.beebehavior.com/Arxive/small_cell_comb_varroa_mites.pdf

20.Evaluating colonies of honey bees for resistance to Varroa jacobsooni, John R. Harbo: http://www.ars.usda.gov/SP2UserFiles/Place/64133000/PDFFiles/301-400/339-Harbo–Evaluating%20Colonies%20of%20Honey%20Bees.pdf

21.The efficacy of small cell foundation as a varroa mite (Varroa destructor) control, A. M. Ellis, G. W. Hayes, J. D. Ellis: http://link.springer.com/content/pdf/10.1007%2Fs10493-008-9221-3

22.Survival of a Commercial Beekeeper in Norway, Hans-Otto Johnsen:

http://www.beesource.com/point-of-view/hans-otto-johnsen/survival-of-a-commercial-beekeeper-in-norway/

23.A multifactorial study of the resistance of honeybees Apis mellifera to the mite Varroa destructor over one year in Mexico, Luis MONDRAGÓN, Marla SPIVAK, Rémy VANDAME: http://www.beelab.umn.edu/prod/groups/cfans/@pub/@cfans/@bees/documents/asset/cfans_asset_317701.pdf

24.Brood cell size of Apis mellifera modifies the reproductive behavior of Varroa destructor, Matías Maggi, Natalia Damiani, Ser- gio Ruffinengo, David De Jong, Judith Principal, Martín Eguaras: http://link.springer.com/content/pdf/10.1007%2Fs10493-009-9314-7

25.Small-cell comb does not control Varroa mites in colonies of honeybees of European origin, Thomas D. Seeley, Sean R. Griffin: http://www.researchgate.net/publication/225570786_Small-cell_comb_does_not_control_Varroa_mites_in_colonies_of_honeybees_of_European_origin

Alternative link to reference 25: http://tinyurl.com/ccnd7z2