A Remarkable Finding in Honey Bee Research
At the recent Hexham AGM we heard how the Association has been invited to contribute funds towards a major new research project. It is codenamed REViVe, for: “Rolling out the Evolution of resistance to Varroa and DWV” and its rationale and aims are outlined in the November issue of BeeCraft¹. DWV is deformed wing virus, the major lethal agent transmitted by varroa mites and the main cause of collapse of varroa-infested colonies. The initial research was summarised in the BBJ supplement of the September issue of “BBKA News”² and it derives from work involving Prof. Stephen Martin of the University of Salford, who presented the recent Rachel Lowther Memorial Lecture on the Asian hornet. That work was carried out on varroa-tolerant bees from the Brazilian island of Fernando de Noronha and also involved virologists at the Marine Biological Station in Plymouth, led by Dr Declan Schroeder.
The science depends on recognition that DWV occurs in several variants, of which the most important are Types A and B. Honey bee pupae infected with Type A develop into adults with underdeveloped abdomens, shrivelled wings and a shortened lifespan, that can lead to colony collapse, whereas infection with Type B does not have these unfortunate consequences.
The modest hero of this study is not a scientist, but a former heating engineer in Swindon named Ron Hoskins. Ron is a thoughtful and very persistent beekeeper and founder of Swindon Honeybee Conservation Group. You may have seen him and his bees last autumn with Chris Packham in a countryside programme, but I first got to know him a decade ago, as the BBKA Slide Librarian who every year provided me with material to illustrate my Beekeeping Beginners’ Course.
For Ron, the present story began in 1994, when he discovered his bees could keep their varroa under control, apparently having developed the ability to groom mites off one another’s bodies³. On that basis he began a programme of breeding which has continued ever since, and since 1994 he has never used chemical control. Instead he collects the dead, fallen mites, counts the proportion that show physical damage and propagates the most effectively resistant colonies.
In 2007 he made a second discovery, that many transparent bee pupal antennae, as well as many baby mites, had fallen into the varroa tray in one hive. This colony was demonstrating another means of varroa control, known as “anti-varroa hygienic behaviour”. This involves house bees uncapping infected brood cells, pulling out the pupae inside and at the same time ejecting the mites hiding within. During this process the pupae’s antennae become detached.
In 2012 a virologist became interested in why, even when some of Ron’s hives had developed a fairly hefty mite population, those colonies did not go down with DWV. He examined the level of infection of the mites with DWV-A and found it to be high. However, by contrast, the level of infection of their hosts, the bees, was very low, although the latter were loaded with DWV-B instead!
The first scientific report was published last October in the advance online publication of the highly prestigious journal “Nature”. 4 The gist of that interpretation is that Ron’s bees had somehow acquired a strong population of the non-lethal variant type B and that this is preventing entry of the lethal Type-A into the bodies of the bees. The phenomenon is known in other circumstances as “superinfection exclusion”, but the way it works is so far unexplained.
The theory the researchers will be investigating in the planned project is that differences in the pathogenicity of DWV types A and B relates to differing capacities of the two forms of the virus to enter certain critical cells in the bees’ bodies. The methods they will use to test this include microscopy with an interesting twist. This is to examine thin sections of bees’ tissues stained with a reagent that fluoresces when illuminated under ultraviolet light. The stain contains fluorescent antibodies directed against protein on the external surface of the viruses, so that their fluorescence then indicates the whereabouts of virus of either type in the bees’ bodies. The aim is to apply this test to tissues from bees infected with either DWV Type A, or Type B. and to see if the pattern of tissue infiltration is different.
Meanwhile, Ron is independently pursuing his own explanation. It will be interesting to see who gets there first!
The discovery of the apparent interaction between lethal and protective variants of the same virus suggests a powerful new way to protect varroa infested colonies. Those who do not yet have varroa-resistant bees owe Ron a sincere vote of thanks.
1. Smith, M. (2015) Bees, Viruses and Varroa . BeeCraft, 97 (11), p. 29.
2. Mordecai, G. J., Jones, I. M. and Schroeder, D. C. (2015) Implications of RNA virus quasispecies: determining the cellular and tissue tropism of deformed wing virus. British Bee Journal Supplement 2, p.10, in BBKA News” No. 222.
3. Hoskins, R. (2015) Honeybee Health. Swindon Honeybee Conservation Group “Really do have Varroa Hygienic Bees!”. The Beekeepers’ Quarterly”, 122, pp 26-28).
4. Mordecai, G. J. Bretell, L. E. Martin, S. J. Dixon, D. Jones, I. M. & Schroeder, D. C. (2015) “Superinfection exclusion and the long-term survival of honey bees in Varroa-infested colonies”. The ISME Journal doi: 10.1038/ismej.2015.186;