Volume 41, Number 4, July-August 2010
|Page(s)||463 - 465|
A scientific note on Varroa destructor found in East Africa; threat or opportunity?*
Note scientifique sur Varroa destructor découvert en Afrique de l’Est : menace ou opportunité ?
Eine wissenschaftliche Notiz über das Auftreten von Varroa destructor in Ostafrika: Bedrohung oder Gelegenheit?
Penn State, Department of Entomology, Center for Chemical Ecology,
501 ASI Building, University Park,
PA, 16802, USA
2 The International Center of Insect Physiology and Ecology (icipe), PO Box 30772-00100, Nairobi, Kenya
3 USDA/ARS Bee Research Laboratory, Beltsville, MD, USA
Corresponding author: M. Frazier, firstname.lastname@example.org,
Revised: 28 September 2009
Accepted: 29 September 2009
Key words: Varroa destructor / Apis mellifera scutellata / Apis mellifera monticola / hygienic behavior
In many areas of the world where it is managed, the honeybee, Apis mellifera, has been plagued by diseases, pests and parasites. Of these, the parasitic mite, Varroa destructor Anderson and Truman (Acari:Varroidae), is considered by many as the most devastating. We found this mite in honeybee colonies throughout Kenya and in Tanzania for the first time in early 2009. Beekeepers surveyed were neither aware of the mite’s presence nor had they observed any negative impact on the survival and/or productivity of their bees.
In March of 2009, we sampled 38 honeybee colonies (likely A. m. scutellata, and possiblyA. m. scutellata hybrids) in seven locations in Central and Eastern Kenya. We employed a common sampling technique to determine mite presence/absence that utilizes powdered sugar to dislodge mites from adult bees (Macedo et al., 2002). An average of 717 ± 43 bees per colony were sampled and Varroa mites were found in all 38 colonies examined with numbers ranging from 3–108 per sample and averaging 26.3 ± 25.9 per colony. In a further similar survey (April–May, 2009) of 125 additional colonies located in the eastern, western and coastal regions of Kenya (69 colonies in 18 locations), coastal Tanzania (18 colonies in 4 locations) including Ugunja and Pemba Islands, collectively referred to as Zanzibar (likely A.m. litorea), and Western Uganda (14 colonies in 4 locations), 87% of the colonies tested positive for Varroa (Fig. 1). Only the 14 colonies surveyed in western Uganda and two of the Zanzibar colonies tested negative for mites. A limited survey of colonies in eastern Ghana (4 locations) found low numbers of Varroa in 2 out of 12 colonies sampled, suggesting that the mite has also spread to certain parts of West Africa.
Varroa sampling locations in Kenya, Tanzania and Uganda.
Fourteen Varroa mites were analyzed via partial sequencing of the cytochrome oxidase 1 gene (CO1). For all mites, CO1 sequence between primer sites Co1F.F and Co1N.R (Evans and Lopez, 2002) was identical with the South Korean haplotype of Varroa destructor (Genbank entry AF106899), the predominant V. destructor lineage worldwide.
The presence of this mite in Africa is highly significant. Honeybees of several different races are native to Africa and their geographic distributions have been partially mapped (Ruttner, 1975). These various races of honeybees are reportedly responsible for pollinating 40–70% of indigenous plants, including some important commercial crops (Allsopp,2004). If Apis colonies in Africa succumb to Varroa as they have in other parts of the world, the results could be devastating to both agricultural production and non-agricultural ecosystems. The introduction of Varroa into South Africa in 1997, coupled with the spread of A. m. capensis led to an initial rapid decline in native honeybee populations over seven years (Allsopp, 2004). Yet 12 years after the mite’s introduction, honeybees of both A. m. capensis and A. m. scutellata, feral and managed populations alike appear to exhibit levels of tolerance that have reduced the pest status of this mite to “incidental”according to Allsopp (2006). He further speculates that increased hygienic behavior and a lack of chemical control used by beekeepers, is in part, responsible for this tolerance.
Hygienic behavior is a well-documented mechanism of disease resistance in honey bees (Rothenbuhler, 1964; Spivak and Reuter, 2001). Spivak (1996) found bees bred for hygienic behavior in the US also detect and remove mite-infested pupae from their colony. Although variable, African bees may naturally exhibit a higher degree of this behavior than European bees and it may vary across races or by geographic area (e.g., Mondragon et al., 2005). In an attempt to understand the apparent absence of American Foulbrood in Africa, Fries and Raina (2003) using the pin-killed brood method, found a considerable level of hygienic behavior (removal rate of 95% in 24 hrs in 7 of 11 colonies) in colonies in an apiary north of Harare, Zimbabwe. In March 2009 we tested 10 colonies for hygienic behavior at The International Center of Insect Physiology and Ecology (icipe) apiary outside of Nairobi (S01°13’27.7”E36°53’50.8”, elevation 1606 m) and 10 colonies in an apiary 34 km east of Mwingi (S0°48’54.1”, E38°18’96.8”, elevation 636 m) using the freeze-killed brood assay (Spivak and Downey, 1998).
Frequency distribution of hygienic behavior in 20 colonies located in two apiaries in Kenya.
African bees appear to deal with mites more effectively than European bees. Hygienic behavior, especially the ability to detect and remove Varroa-infested brood is likely one important mechanism of mite tolerance in these bees. Yet hygienic behavior along with a lack of miticide use is unlikely to account for the levels of tolerance to Varroa expressed in the honeybees of East Africa. Other behaviors, such as grooming, increased swarming, absconding, and even management practices (or the lack of them, i.e., the use of acaricides) are likely to be important. In Brazil, Africanized honey bee populations have maintained resistance toward mites, although the relative importance of intrinsic bee traits (Correa-Marques et al., 2003) versus selection imposed by bee management practices and the avoidance of chemical acaricides, is unclear. It may be that the highly genetically variable honeybee races in Africa contain evolutionary answers to limiting the impacts of Varroa mites and other major bee diseases. If so, understanding these mechanisms may be all-important not only for preserving agriculture in developed countries but also for maintaining the biological diversity of tropical ecosystems.
This project was funded by a grant from USDA CSREES-ISEC and with additional funds from icipe and IFAD. We would also like to thank beekeeping technicians James Nganga Kimani, Joseph Kilonzo Wambua and Tom McCormack, who assisted with the sample collection and hygienic behavior assays and Kenyan beekeepers who allowed us to sample colonies in their respective apiaries.
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© INRA/DIB-AGIB/EDP Sciences, 2009