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Milbrath M.O.,Michigan State University | van Tran T.,Michigan State University | van Tran T.,Bee Research and Development Center | Huang W.-F.,University of Illinois at Urbana - Champaign | And 4 more authors.
Journal of Invertebrate Pathology

Honey bees (Apis mellifera) are infected by two species of microsporidia: Nosema apis and Nosema ceranae. Epidemiological evidence indicates that N. ceranae may be replacing N. apis globally in A. mellifera populations, suggesting a potential competitive advantage of N. ceranae. Mixed infections of the two species occur, and little is known about the interactions among the host and the two pathogens that have allowed N. ceranae to become dominant in most geographical areas. We demonstrated that mixed Nosema species infections negatively affected honey bee survival (median survival= 15-17 days) more than single species infections (median survival = 21 days and 20 days for N. apis and N. ceranae, respectively), with median survival of control bees of 27 days. We found similar rates of infection (percentage of bees with active infections after inoculation) for both species in mixed infections, with N. apis having a slightly higher rate (91% compared to 86% for N. ceranae). We observed slightly higher spore counts in bees infected with N. ceranae than in bees infected with N. apis in single microsporidia infections, especially at the midpoint of infection (day 10). Bees with mixed infections of both species had higher spore counts than bees with single infections, but spore counts in mixed infections were highly variable. We did not see a competitive advantage for N. ceranae in mixed infections; N. apis spore counts were either higher or counts were similar for both species and more N. apis spores were produced in 62% of bees inoculated with equal dosages of the two microsporidian species. N. ceranae does not, therefore, appear to have a strong within-host advantage for either infectivity or spore growth, suggesting that direct competition in these worker bee mid-guts is not responsible for its apparent replacement of N. apis. © 2014 Elsevier Inc. Source

Beaurepaire A.L.,Martin Luther University of Halle Wittenberg | Truong T.A.,Bee Research and Development Center | Fajardo A.C.,University of the Philippines at Los Banos | Dinh T.Q.,Bee Research and Development Center | And 3 more authors.

The ectoparasitic mite Varroa destructor is a major global threat to the Western honeybee Apis mellifera. This mite was originally a parasite of A. cerana in Asia but managed to spill over into colonies of A. mellifera which had been introduced to this continent for honey production. To date, only two almost clonal types of V. destructor from Korea and Japan have been detected in A. mellifera colonies. However, since both A. mellifera and A. cerana colonies are kept in close proximity throughout Asia, not only new spill overs but also spill backs of highly virulent types may be possible, with unpredictable consequences for both honeybee species. We studied the dispersal and hybridisation potential of Varroa from sympatric colonies of the two hosts in Northern Vietnam and the Philippines using mitochondrial and microsatellite DNA markers. We found a very distinct mtDNA haplotype equally invading both A. mellifera and A. cerana in the Philippines. In contrast, we observed a complete reproductive isolation of various Vietnamese Varroa populations in A. mellifera and A. cerana colonies even if kept in the same apiaries. In light of this variance in host specificity, the adaptation of the mite to its hosts seems to have generated much more genetic diversity than previously recognised and the Varroa species complex may include substantial cryptic speciation. Copyright: © 2015 Beaurepaire et al. Source

Forsgren E.,Swedish University of Agricultural Sciences | Wei S.,Chinese Academy of Agricultural Sciences | Guiling D.,Chinese Academy of Agricultural Sciences | Zhiguang L.,Chinese Academy of Agricultural Sciences | And 5 more authors.

Populations of Apis mellifera and Apis cerana in China and Vietnam were surveyed in order to study possible pathogen spill-over from European to Asian honeybees. This is the first survey of the prevalence of honeybee pathogens in apiaries in Vietnam, including pathogen prevalence in wild A. cerana colonies never in contact with A. mellifera. The bee samples were assayed for eight honeybee viruses: deformed wing virus (DWV); black queen cell virus (BQCV); sac brood virus (SBV); acute bee paralysis virus (ABPV); Kashmir bee virus (KBV); Israeli acute paralysis virus (IAPV); chronic bee paralysis virus (CBPV); and slow bee paralysis virus (SBPV), for two gut parasites (Nosema ssp.) and for the causative agent for European foulbrood (Melissococcus plutonius). The Vietnamese samples were assayed for Acarapis woodi infestation. No clear evidence of unique inter-specific transmission of virus infections between the two honeybee species was found. However, in wild A. cerana colonies, the only virus infection detected was DWV. With findings of IAPV infections in Chinese samples of A. cerana colonies in contact with A. mellifera, inter-specific transmission of IAPV cannot be ruled out. BQCV was the most prevalent virus in managed colonies irrespective of bee species. We did not detect the causative agent of European foulbrood, M. plutonius in wild or isolated colonies of A. cerana in Vietnam or China; however, low incidence of this pathogen was found in the Asian host species when in contact with its European sister species. No evidence for the presence of A. woodi was found in the Vietnamese samples. © 2014, The Author(s). Source

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