A Mathematical Model of Intra-Colony Spread of American Foulbrood in European Honeybees (Apis mellifera L.).

American foulbrood (AFB) is one of the severe infectious diseases of European honeybees (Apis mellifera L.) and other Apis species. This disease is caused by a gram-positive, spore-forming bacterium Paenibacillus larvae. In this paper, a compartmental (SI framework) model is constructed to represent the spread of AFB within a colony. The model is analyzed to determine the long-term fate of the colony once exposed to AFB spores. It was found out that without effective and efficient treatment, AFB infection eventually leads to colony collapse. Furthermore, infection thresholds were predicted based on the stability of the equilibrium states. The number of infected cell combs is one of the factors that drive disease spread. Our results can be used to forecast the transmission timeline of AFB infection and to evaluate the control strategies for minimizing a possible epidemic.

Host Specificity in the Honeybee Parasitic Mite, Varroa spp. in Apis mellifera and Apis cerana.

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.

Radiation inactivation of Paenibacillus larvae and sterilization of American Foul Brood (AFB) infected hives using Co-60 gamma rays.

The effectiveness of gamma radiation in inactivating the Philippine isolate of Paenibacillus larvae was investigated. Spores of P. larvae were irradiated at incremental doses (0.1, 0.2, 0.4, 0.8 and 1.6 kGy) of gamma radiation emitted by a 6°Co source. Surviving spores were counted and used to estimate the decimal reduction (D10) value. A dose of 0.2 kGy was sufficient to inactivate 90% of the total recoverable spores from an initial count of 105- 9 × 10³ spores per glass plate. The sterilizing effect of high doses of gamma radiation on the spores of P. larvae in infected hives was determined. In this study, a minimum dose (D(min)) of 15 kGy was tested. Beehives with sub-clinical infections of AFB were irradiated and examined for sterility. All the materials were found to be free of P. larvae indicating its susceptibility to γ-rays. After irradiation, there were no visible changes in the physical appearance of the hives' body, wax and frames. Thus, a dose of 15 kGy is effective enough for sterilization of AFB-infected materials.