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Posted 08 October 08

A New Slant on Chalk Brood Disease?

Eric McArthur

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(By kind permission of BKQ Sept 08. Vol.93 p.29)

Chalk Brood, (Ascosphaerosis), the fungal disease caused by Ascosphaera apis (Massen ex Claussen) Olive and Spiltoir, is not normally a condition which affects the viability of a honey bee colony. However there are situations where it can be so severe that the survivability of the colony is threatened.

Professor Len Heath investigated the disease thoroughly in an excellent article in Bee World, Vol 66, No1, 1985. Many theories for the incidence and spread of the disease are mooted in his excellent article and the condition has been exhaustively documented on a world wide scale over the years. The disease seems to disappear for a period and then suddenly arise again. In America the disease was widely prevalent in Georgia, Iowa and Florida in the 1920s. At that time beekeepers reported that they re-queened colonies on a continuous basis and the condition then disappeared. However outbreaks of chalk brood reappeared in widely separate locations in North America within a few years in the late 1960s. It has been suggested that the Italian breeding stock of the 1920s had a greater resistance to the disease and that this could explain the apparent disappearance of the disease in the 1920s. Another theory postulates that the genes for increased susceptibility to chalk brood were introduced into breeding stocks and transmitted with queens and package bees all over America.

It has also been suggested that its reappearance in the late 1960s was due to mutation in the fungal stock. However parallel studies of the British and American strains of A. apis have shown no major and consistent morphological or physiological differences to confirm this theory.

Another possibility which was proposed was that changes in weather patterns could be responsible. This idea was deemed improbable because such changes appear to fall within the range of weather conditions in those parts of the world where chalk brood is found.

Chalk brood was found in New Zealand in 1957 by D.W.A. Seal, who was of the opinion that it had been present for some time. However the Principle Research Officer at Wallaceville described Seal’s samples as ‘diseased larvae with the appearance of chalk brood’. The fungal mycelium which permeated the larvae was only tentatively identified by him as A.apis. He went on to state that chalk brood was seldom found in NZ, even in areas having high rainfalls, implying that it was occasionally found in such regions. Reports on most of the 200,000 honey bee colonies in NZ examined annually dating from 1957 showed no incidence of chalk brood until 1984, when it was found in Kerikeri in North Island. A suggestion regarding the NZ situation is that A.apis is a latent endemic condition which only manifests itself when an environmental event occurs which activates the disease to clinically observable levels.

Observations made by myself in late spring /early summer 2007 and again in mid summer 2008 caused me to re-visit Prof Heath’s Bee World article to find out if he had mentioned anything about a phenomenon that came to my attention relating to chalk brood on both of these occasions.

The Clyde Area Beekeepers’ Association decided in November 2006 to try to establish a project to foster the honey bee gene pool in the West of Scotland using the apiary of the Glasgow and District Beekeepers’ Association. I was appointed Project Leader! The project was ambitious to say the least because at the time, early winter, there were only two surviving colonies in the apiary, however there was a sufficient amount of equipment of mixed design with which to begin.

The original two colonies were given VIP treatment and although having queens of indeterminate age came out of the winter relatively strong. As Project Leader, I decided that I would sacrifice 10 of my own colonies to get the project going. The original two colonies were fed to encourage build up – these would supply the drones for the new queens. All went according to plan –April 2007 was a beekeeper’s dream and by early May I was able to make up 10, 4 frame queenless nuclei and transport them to the CABA apiary for mating of the virgins produced. Despite May turning out to be as bad as April had been good the virgins were mated and laying by early June. All seemed to be on course for a good start to the project – then disaster struck - 6 of the 10 nucs were affected by the heaviest infestation of chalk brood I have ever seen and seemed to be ‘write offs’. Desperate situations require desperate measures and inspirational thinking. The infested combs were shaken free of the adhering bees, empty drawn deep frames previously fumigated with acetic acid were used to replace the discarded (and destroyed by fire!) frames. The bees were then fed with 2.5 litres of 1:1 sugar syrup and a sponge soaked with 20 mls, 60% formic acid inserted right on the frame tops for good measure (inspirational!!). The bees were left for a couple of weeks before being examined again. That examination was a revelation and will remain with me for the rest of my life – each and every one of the previously, seemingly doomed nuclei had a full comb of healthy sealed brood and to cap it all the chalk brood condition never appeared again in the apiary. We had an Open Day on the 21st July 2007 and sold 7 – 5 frame nucs bursting with bees to beginners attending that day. Every colony was opened for examination, Ian Craig the SBA President, who had been informed of the chalk brood problem at the time it occurred and who was also at that Open Day and can confirm not only that no chalk brood disease was present but also that the bees handled perfectly with no-one being stung or even threatened. A minor miracle!!

The CABA apiary bees exhibited negligible chalk brood this year 2008 and again the Open Day on 20th July saw another six beginners receive their 5 frame nucs again bursting with bees. Ian Craig was again present at the Open Day!

The weather in Scotland over the summer of 2008 must be a near record for continuous unfavourable weather and all colonies in the CABA apiary and my own outfit were fed more or less continuously. There was never a time when either syrup, fondant or sugar bags was not available to the bees – and it paid off by keeping the colonies in good heart. However one colony in one of my out-apiaries slipped through the net - I came back from holiday in late June, just at the end of the June Gap and on examining the colonies found to my horror that chalk brood was back with a vengeance in one strong nuc, which had been missed and not fed before I went on holiday. The condition was nowhere near the severity of the previous year in the CABA apiary but uncomfortably high. I did not remove any frames but I fed 3 litres of 1:1 sugar syrup to the colony – unfortunately I did not have my formic acid with me – so the bees only got the syrup. I went back the following week – with more feed and the requisite formic acid. I opened the colony expecting to find the disease condition, at best the same as the previous week, or at worst, epidemic in the colony.

To my astonishment there was no trace of chalk brood and the cells that had contained the mummies had either very young larvae or were full of uncapped honey - the feeder was empty!

To cut a long story short I am convinced, despite all the science and scrutiny that has gone before that the explanation for out breaks of chalk brood has nothing to do with queen quality, genetic resistance or good house keeping on the part of the colony. In my opinion the disease is a condition of inadequate food and more specifically the dearth of income of nectar or the lack of liquid feeding. The application of the formic acid in the 2007 case I am certain was not of any great significance. But that is not to say that used hive furniture should not be adequately sterilised before use.

At present I am unable to continue with my Chalk Brood postulation – none of my colonies now has any evidence of the disease. Perhaps interested parties having an A.apis presence might be moved to confirm or deny this submission.

I strongly feel that the larval stage hunger or competition for food is a critical factor in the development of the A.apis in the honey bee colony.

As an aside looking at another brood disease, European Foul Brood, which, it is accepted, has associations with larval hunger and competition for food – it has been observed that the incidence of EFB is extremely low or not clinically observable in colonies which are husbanded in areas with excellent forage conditions, in fact Bailey in his book “Infectious Diseases of the Honey Bee” states on page 139, paragraph (c). The effect of beekeeping on EFB - “In localities with uninterrupted nectar flows, where colonies can grow unhindered each year, (EFB) infection may remain slight and the disease unapparent”. I put forward the postulation that the same conditions hold for Chalk Brood and that by feeding colonies heavily in times of dearth will go a long way to maintaining healthy bees.

In fact the use of antibiotics to treat EFB might just be a waste of time, effort and money.

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