CHALK BROOD IN ETHIOPIA
Published in Bees for Development Journal 78 (March 2006) Desalegn Begna Rundassa, Holetta Bee Research Centre, Ethiopia
Chalk brood is a disease of honeybee larvae caused by the fungus Ascosphaera apis, which causes the death and mummification of sealed honeybee brood, and with the consequent weakness of the colony. It is widespread amongst honeybees in Europe and North America. In Africa the only report of chalk brood has been from Tunisia (Heath, 1985). The disease is spread by robbing, drifting bees and by the normal practices of beekeeping (Warhurst, 1998). Ascosphaera apis produces sticky spores, which are commonly present on adult bees and all surfaces within occupied hives. The disease develops only if the brood is physiologically stressed in some way, for example chilling.
In Ethiopia, the existence of two adult honeybee diseases Nosema apis and Melpighamoebae mellifica and their distribution was studied and reported (Gezahegn & Amsalu, 1991; Desalegn & Amsalu, 1999). Until now there has been no record on the existence of any honeybee brood diseases in the country.
Materials and methods
The survey transects and beekeepers to be surveyed were selected randomly. A survey was carried out around the Holetta area on beekeeper’s colonies, and at Gedo demonstration site about 150 km west of Holetta.
Experimental time and colony size
Following the brood rearing season October 2000 to January 2001, 276 colonies at 13 survey sites were inspected externally and internally for signs of chalk brood disease.
Sample collection and laboratory diagnosis
Colonies showing any symptoms of chalk brood: dead infected larvae left uncapped by nurse bees in the comb cells, and mummies at the hive entrances, on the hive floor and on the ground perpendicular to the hive opening, were examined. From 13 apiary sites, larval mummies were collected from eight apiaries that were found to display positive signs of the disease. Overall 240 black mummies of honeybee larvae from 48 bee colonies (five per colony) were collected. Each mummy was macerated separately in a sterile mortar with distilled water to prepare suspensions containing Ascosphaera apis from each site. The suspensions were filtered through fine cloth and the fungus was grown in the laboratory, using Potato Dextrose Agar containing antibiotic to avoid any bacterial contamination, on petri dishes. After eight days, microscopic examination of the cultures was made to determine the size of the spore cysts and spore balls (Spiltoir & Olive, 1955; Skou, 1972; Bailey, 1981, Bissett, 1988). Photographs were taken of the affected brood combs and fungus cultures.
Microscopic examination of the culture revealed that the range of the size of the spore cysts and the spore balls falls within the standard size described for Ascosphaera apis by Spiltoir and Olive (1955), see Table 1. From 13 inspected apiaries, eight (66.7%) were found positive to Ascosphaera apis (Table 2).
Out of 276 inspected colonies, 48 (17.4%) were found tainted with chalk brood fungus. The prevalence of the fungus among the infected apiary sites ranged from 0-100%. All colonies infested with chalk brood fungus Ascosphaera apis have revealed the signs of the disease either externally or internally. The disease was particularly rigorous and widely distributed in the apiaries of Tesfaye and Mariam (Table 2), which are owned by private farmer beekeepers and within 5-10 km from Holetta Centre. During the survey it was observed that much of the affected brood was drone brood, during October.
Discussion and conclusion
Since the beginning of 2001, the presence of Ascosphaera apis has been confirmed in Ethiopia. However, as the main objective of this study was only to detect the presence of chalk brood in the country for the first time, no attention was given to compare its infestation level among colonies in the same apiary. Also, no attempt was made to compare colony infestation level at different apiaries.
Diseases of fungal origin are more prevalent in damp and cool conditions and Ascosphaera apis grows best when the brood is chilled. In this case many of the incidences were in October, when the temperature sometimes drops below 0°C. Chalk brood disease is most commonly found on the outer fringes of the brood combs and as a result drone brood is more susceptible to the disease. In this survey it was noticed that drone brood rearing was completely discontinued in the colonies seriously affected by chalk brood disease. The dismantling and clearing of the drone larvae and pupae by the bees was observed in the affected colonies. The assumption is that the bees give priority to nursing and warming brood that will grow into worker bees as a replacement stock rather than taking care of drone brood for breeding in these adverse conditions. Gochnauer et al (1975) also documented that when the colony clusters due to cool temperatures, the population of adult bees is insufficient to maintain ideal brood temperatures, particularly on the periphery of the brood. Thus, chalk brood disease is most likely to appear in brood unprotected by the cluster, which usually includes the drones.
Since this survey report many complaints about chalk brood have come from different apiaries at the Centre and from farmer beekeepers.
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