Honeybee diseases in Nepal
by Otto Boecking (1) and Wolfgang Ritter(2)
(1) Institut fiir Landwirtschaftliche Zoologie und Bienenkunde der Universitat, Bonn, Germany
(2) Tierhygienisches Institut, Freiburg, Germany
Honeybees are present in Nepal’s temperate mountain region and in the hot, humid, sub-tropical terai region. Indigenous honeybee species are Apis cerana, Apis dorsata, Apis florea and Apis laboriosa. Honey hunting by professional hunters and collective village groups is a long established activity in Nepal, exploiting the giant honeybee Apis dorsata and the rock bee Apis /aboriosa.
Beekeeping with Apis cerana is part of Nepal's cultural heritage. The most common type of beekeeping is with Apis cerana in log, wooden box, clay and wall hives, which have fixed combs. Various projects have introduced several types of movable-frame hives, supplemented by training and extension services, in attempts to improve beekeeping management techniques with Apis cerana.
Bee diseases reduce potential
The presence of bee disease is one of the main problems facing beekeepers world-wide. A short survey of the present status of bee disease in Apis cerana, with particular concern for Thai sacbrood virus infestation, and Varroa jacobsoni and Tropilaelaps clareae mite infestation in Apis mellifera beekeeping was initiated by AP!-Promo-GTZ (Germany) in March 1998. Information and experiences were exchanged with local beekeepers about these diseases and possible control strategies.
This survey was only a short study. The information source was direct inspection for clinical symptoms of randomly selected bee colonies in each apiary. All colonies investigated were in movable frame hives, which allowed a check of the colonies frame by frame. Bees and brood samples were collected for laboratory analysis.
Diseases in Apis cerana
Based on clinical symptoms, Thai sacbrood virus, European foulbrood and Varroa jacobsoni were present in the inspected Apis cerana colonies. Thai sacbrood virus was found in three colonies (out of 34 inspected). Clinical symptoms are not enough to determine which disease actually threatens the bee colonies. This is because many bee diseases show similar clinical symptoms although they have different causative organisms.
To determine whether Thai sacbrood virus was the cause of the clinical symptoms, laboratory analysis was carried out: in two of three cases this confirmed the clinical symptoms. Visiting three apiaries the beekeepers claimed that their colonies suffered from Thai sacbrood infestation.
Any clinical symptom could prove the beekeepers’ assumption. In these cases the bee colonies suffered from poor pollen and honey supplies, and the bees were already eating their own brood. In two cases the colonies were being robbed by other colonies. All these cases showed poor management of the colonies by the beekeepers.
There are no chemical cures for Thai sacbrood disease, and many beekeepers are treating their colonies with antibiotics, which might increase the development of resistance to bacteria in the future. EFB was found in 11 colonies (out of 34 inspected) and confirmed by laboratory analysis. The infestation level with EFB of all colonies investigated did not reach destructive levels, since the bees themselves try to reduce the disease by hygienic nest cleaning behaviour.
The incidence of Varroa jacobsoni is low in Apis cerana and it causes no notable damage. Although this ectoparasitic mite regularly infests Apis cerana colonies, many Apis cerana beekeepers in Nepal have never seen a Varroa mite in their colonies, due to the low infestation levels.
INDIGENOUS HONEYBEES IN THE HIMALAYAS
Since 1993 the Austrian Ministry of Foreign Affairs has supported a project to conserve and utilise indigenous honeybees in Nepal. In 1999 the project was widened to include the Hindu Kush Himalaya Region. The project is managed by Austroprojekt GmbH (Vienna) and based at the International Centre for Integrated Mountain Development (ICIMOD) in Kathmandu. B&D will bring regular features about the word of the project throughout 2001 and 2002. To provide context for the importance and need for this project, we are starting the series with this summary of the honeybee disease situation in Nepal.
Apis cerana: An Asian species of honeybee that can build a series of parallel combs and can be kept in hives.
Apis dorsata, Apis florea, Apis laboriosa: Asian species of honeybees. These bees build single combs and cannot be kept inside man-made hives.
Apis mellifera: This is the species of honeybee found naturally throughout Africa, Europe and the Middle East. In recent years European races of Apis mellifera have been introduced to many countries of Asia, including Nepal.
European foulbrood: European foulbrood (EFB) is primarily caused by the bacteria Mellisococcus pluton. EFB occurs in Apis cerana and Apis mellifera.
Sacbrood: This disease is caused by the Sacbrood virus and is found in Apis mellifera.
Thai sacbrood: This disease is caused by the Thai sacbrood virus, and is found in Apis cerana.
Tropilaelaps clareae: This is a mite. It occurs naturally in Apis dorsata and does not cause problems for this species. Tropilaelaps clareae does cause problems when present in Apis mellifera,
Varroa jacobsoni: This is a mite. It occurs naturally in Apis cerana and does not cause serious problems for this species. Varroa jacobsoni does cause problems when present in Apis mellifera.
Diseases in Apis mellifera
During this survey five beekeepers, keeping a total of 155 colonies of Apis mellifera were visited. 14 randomly selected bee colonies were carefully inspected for clinical symptoms of bee diseases. Based on clinical symptoms, Sacbrood virus, EFB, Varroa jacobsoni and Tropilaelaps clareae were present in the inspected Apis mellifera colonies. All inspected bee colonies were infested with the Varroa mite, but at very low levels.
This is because the beekeepers treat their colonies with acaricide regularly throughout the whole year. This will create problems in the future. Already it is well known that chemical residues of the treatments accumulate in honey and wax, a basis for the development of resistant mites. Honey contaminated with chemical residues will not be acceptable for international markets.
Some of the colonies were highly infested with Tropilaelaps clareae to the extent that secondary infections had already started to destroy the colonies. Sacbrood disease and EFB were evident. Both diseases, and bees with deformed wings (possibly due to the deformed wing virus) are indications of secondary infections. Laboratory analysis confirmed the clinical symptoms of Sacbrood virus and Deformed wing virus.
Commercial beekeepers are known to migrate Apis mellifera colonies from the Kathmandu Valley into the terai region, in order to exploit the temporary local nectar flows. Apis dorsata occurs naturally in the terai and is the original host of the mite Tropilaelaps clareae.
The moment the beekeepers migrate their Apis mellifera colonies into the terai in October Tropilaelaps clareae mites start to infest the Apis mellifera colonies. Moving the colonies back into the Kathmandu Valley, the Tropilaelaps clareae mites are brought into geographical regions where these mites are not endemic.
Beekeepers with Apis mellifera claim at the infestation or their colonies with Tropilaelaps clareae is more destructive than the infestation with Varroa.
However acaricides that are effective only on Varroa jacobsoni are used extensively without any impact on Tropilaelaps clareae, leading to the increasing population growth of this mite. Both mites give problems only original hosts, Apis cerana and Apis dorsata have during thousands of years of evolution developed balanced host/parasite interrelations with these mites.
Exchange of experiences
Only a few of the Apis mellifera beekeepers are using their profession as their sole income source, most need additional income resources. Other products like pollen, propolis and wax are not commercialised.
Beekeepers are not organised in groups and associations, and little or no help is provided by the government. Although information and experience exchange is helpful for any beekeeping community, ‘competitive thinking’ predominates between the beekeepers (perhaps typical of some beekeepers world-wide). This, and the fact that colony theft leads to the problem that bee colonies are kept near to the farmers’ houses. Since the foraging range of honeybees (especially Apis cerana) is limited this hinders the bees from reaching enough pollen and nectar sources during some of the year.
As a consequence the colonies are ‘stressed’ and highly susceptible to diseases like Thai sacbrood virus. Beekeeping with Apis cerana is decreasing. Some beekeepers switch over to Apis mellifera in hope of greater productivity and to overcome problems with Thai sacbrood disease. However, keeping Apis mellifera colonies in Nepal is possible only with regular use of many chemicals to treat for many bee diseases.
Some Apis cerana beekeepers showed excellent knowledge about beekeeping management techniques. Their colonies were in good and heathy condition. Obviously there is a large potential for Apis cerana beekeeping in Nepal. Chemical treatments are not necessary to keep healthy and productive Apis cerana colonies as long as they have enough pollen and nectar sources during the year.
Thai sacbrood disease is perceived by more than 90% of the Apis cerana beekeepers as the most critical pest and disease, followed by EFB. The disease tends to be seen in early spring and early autumn. It is often claimed that Thai sacbrood disease destroys the colonies, although this is not always the real reason.
The survey of existing Varroa control methods revealed that there is an urgent need to establish additional and new control methods for use by Apis mellifera beekeepers, since the intensive use of chemical acaricides has limitations.
The natural nectar and pollen resources and potentials are not yet fully explored in Nepal. There is a requirement for the expansion of the beekeeping industry.
There is a high demand for training in basic bee management techniques necessary for the different groups of beekeepers.
This is especially necessary concerning bee disease control, since the methods used have limitations and will produce additional problems due to residues in the bee products.
It is claimed that beekeeping with Apis cerana is decreasing among beekeepers because of the frequent incidence of Thai sacbrood virus disease. There is a high correlation between the susceptibility of a colony to disease and poor management techniques. It is necessary to prove that managed colonies provided with enough pollen and nectar sources are as susceptible to Thai sacbrood infection as non-managed ones. This applied research should take place in Nepal.
The authors are grateful for the help of Ms S Basnet, Dr H Pechhacker, Dr N M Saville, Mr Sharma, Mr K K Shrestha, Mrs M Shrestha, Mr A N Shukla, and all the beekeepers who allowed us to check their colonies for bee diseases.
Also to API-PROMO-GTZ, Germany for initiating the survey and providing partial funding to Otto Boecking.
Useful reading in B&D
How Apis cerana keeps Varroa in check (Otto Boecking) B&D 48 (1998)
Apis mellifera v Apis cerana in the North of Thailand (H Pechhacker and N Juntawong) B&D 30 (1994
Zooming in on Nepal B&D 21 (1991)
Thai sacbrood disease occurs in cycles. Since this survey, the incidence of Thai sacbrood virus has decreased and is currently not a problem for Apis cerana bees and beekeepers in Nepal. The disease seems to recur in 7-10 year cycles.