Hon. Newsletter Editor:
Peter Edwards
E-mail: beekeepers@stratford-upon-avon.freeserve.co.uk

WINTER LOSSES

Have you sent in your winter loss return?   If not, please do it now!

I will publish a full analysis of the figures in next month’s newsletter, but interim figures for 19 members show average losses of 11%.  This is well within normal limits, but if we exclude one member who had an unusually high loss, then the figure falls to just 9%.  There is no CCD here!
Peter Edwards

APIARY MEETING - 15 April

We had a good first apiary meeting this year; the weather was kind to us and it was good to see a number of new members in attendance.  We numbered all the brood boxes temporarily with a marker pen (I bought a complete set of plastic numbers at Stoneleigh, so can do the job properly when I have a few minutes) and set up a record book with loose leaf pages.  Each queen was allocated a number and this was recorded with their colony numbers.  All queens were found, clipped and marked.  Of the six colonies put into winter, one has died out (queen failure) and one had a new queen that appears to be an early supersedure as there were only two frames of eggs present (David has since inspected them and reports that there is good worker brood now).

The BIG plans to start queen rearing on Saturday 12 May (all welcome) with more work at the normal Association meeting on 20 May.  Why not come along and get involved?
Peter Edwards

BIBBA SEMINAR - MORE IMPORTANT INFORMATION ON VARROA

Terry, David and I attended the BIBBA AGM and Seminar at Stoneleigh on 22 April this year.  There were two lectures in the morning.  Dr Mervyn Eddie updated us on the progress made with ‘Project Discovery’, which is a programme designed to identify sources of native honeybees in the UK.  The project is now being organised in a very professional manner and will start soon in Scotland and Eire; England will follow later.  I look forward to being able to report on progress in the future.

Of rather more immediate interest was the lecture on varroa tolerance and resistance given by Dr Stephen Martin, who is now based at Sheffield University.  Stephen always seems to be able to provide so much useful and relevant information.  I wrote in the February 2002 newsletter about his lecture to the Central Association, when he explained why colonies infested with varroa die in winter.  At the BIBBA meeting he added to our knowledge on the viruses vectored by varroa and also explained how mites have become resistant to pyrethroids (the active chemicals in Bayvarol and Apistan).  I have therefore decided to summarise this important lecture below, as it provided the answers to many questions that are currently being asked - not least about CCD, winter losses and ‘Marie Celeste’ hives.

VARROA TOLERANCE/RESISTANCE IN APIS MELLIFERA
(read this if you don’t read anything else!)

Stephen first gave a brief review of the history of varroa and of his own extraordinary career, including his time at the NBU - where he developed the varroa calculator - and some interesting examples of work at Rothamsted with small colonies in cages where every bee numbered as it emerged and a note made of whether it was parasitised by varroa.  Bees were collected when they died and then checked for viruses.  All of his published papers are available at http://lasi.group.shef.ac.uk/smartin.html.

Viruses

Viruses are important because of the fact that they, rather than the varroa, kill colonies.  Viruses can exist in bees without causing disease (this is known as an inapparent infection) because approximately 100,000,000,000,000 virus particles are required to cause disease when applied by ‘normal’ routes (e.g. ingestion).  However, if a varroa mite picks up virus from the haemolymph (blood) of an adult bee and then injects it into a larva when feeding, only 100 particles are required to have the same effect.  This why varroa is such a problem - it transmits virus from adults to larvae in a way that would not normally happen.

Stephen made the point that virus infected bees often die away from the hive - leaving the hive empty, or with just the queen and a few bees - the so-called ‘Marie Celeste’ syndrome.  Perhaps the crucial point he made was that when varroa first arrived in this country these viruses were rarer, so varroa numbers could be very large, perhaps 10,000-20,000 per colony.  They did not cause much damage because they were not transmitting virus.

Now, after many years of varroa spreading them, viruses are endemic as inapparent infections in adult bees, so if a mite feeds on an adult bee it is now very likely to pick up virus particles which it will then transmit to any larvae on which it feeds - and remember that only 100 particles will cause disease when the particles are injected into the larvae in this way.

We had a detailed look at the effect of Deformed Wing Virus (DWV) and Acute Paralysis Virus (APV) on the life expectancy of bees and the impact on the colony.

APV virus will cause the colony to collapse very quickly - it kills in days, but DWV will cause the colony to decline more slowly.  This increase in the amount of virus in our colonies is the main reason why varroa is a much greater problem now than when it first arrived, and the differences in the effect of each virus explains why some colonies collapse in days whilst others go into slow decline.

There are at least 14 viruses that affect bees - and we do not know what impact they all have.  The only solution is to keep numbers of varroa low - certainly well below 2000 [Ritter gave 1000 as the critical figure at Apimondia in 2005. PE].  You will probably not see varroa if there are only 2000 in a colony.

Bees in the tropics and Africanised bees survive because of constant brood rearing providing new bees; in temperate climates where brood rearing is reduced or ceases during the winter months, the dying bees are not replaced and the colony therefore dies out.

Resistant mites

There were three possible ways that varroa could have developed resistance:

·         grow a thicker cuticle - to protect them from the pyrethroids;

·         produce detoxifying enzymes in their haemolymph to destroy the pyrethroids;

·         make changes to the 'sodium channel' in their cell walls so that the pesticide cannot enter the cells.

Recent research suggests that varroa has become resistant by the sodium channel route and that this probably occurred as a mutation in a single mite in Sicily; mites are virtually 'clonal' (i.e. genetically identical due to brother/sister mating) and it seems likely that all the resistant mites may have spread from this one mite.  Mites have not become resistant because beekeepers have misused treatments [as we were once led to believe. PE].  This is evidenced by the fact that mites were originally spread around the world by man and the resistant mites are following the same route - we do not seem to have learnt!

The cost of resistance to the mite

Developing resistance may have an ongoing ‘cost’ to an organism, such as varroa, e.g. growing a thicker cuticle takes valuable resources and this may reduce the mite’s ability to reproduce; but sometimes it may have no cost, e.g. a change to sodium channel.  If there is a cost, then withdrawing the pesticide causes the mite to revert to its original susceptible form and the treatment will work again (until resistance develops  once more); if there is no cost (as in this case) then mites will stay resistant as there is no advantage in reverting.  This is bad news for beekeepers, as it means that once resistance to pyrethroids has become common, then those treatments may be ineffective indefinitely [not what we were given to believe when resistance first appeared. PE].  This suggests that both Apistan and Bayvarol will never work again and beekeepers must look for alternative treatments.

Breeding and Selection for Resistance

No colonies (except for Africanised bees) have been able to survive indefinitely.  Stephen gave an example of large numbers of hives that were taken to an island off Scandinavia and given no treatment in the hope that resistant colonies would develop - all died.  Some beekeepers have been checking dead mites for damage, hoping that this indicated that bees were attacking the mites, but Stephen told us that the damage is actually caused by bees removing dead mites from cells (a percentage die in the cells) - not by bees attacking mites.

Asian hornets

Finally, Stephen told us that the Asian hornets (Vespa velutina) that have recently appeared in Southern France, are probably more of a danger to the public than to bees!  Apparently they are a small hornet and nothing like the mandarin hornet that is sometimes shown devastating a colony of bees in about thirty minutes.
Peter Edwards

THE ASIAN HORNET (Vespa velutina) - ANOTHER VIEW!

The French honey industry is under threat from hordes of bee-massacring oriental hornets, the Daily Telegraph reports.  The forests of Aquitaine, in south-west France, now play host to swarms of the Asian Hornet, Vespa velutina, which is believed to have arrived there "from the Far East in a consignment of Chinese pottery in late 2004".  The attacker wasps are "gigantic," says Thomas Seeley of Cornell University, who studies bee behavior.  Of all social insects, the species has the largest workers, with wingspans that can stretch 5 centimeters.  The wasps build large versions of the papery nests of hornets found in North America, and they specialize in breaking into other social-insect nests and carrying off larvae as food for young wasps.  "I've seen a single wasp overwhelm a colony of 6,000 bees" of a species that doesn't make heat balls, says Seeley.  The invader wasp stands at the nest's entrance as one guard bee after another comes out to defend its home.  "The wasp cuts the guard into pieces ... and waits for the next one," says Seeley.  When all the defenders are dead, "the wasps strip-mine out the larvae," he reports.