Slow bee paralysis virus and its transmission in honey bee pupae by Varroa destructor

The role of the parasitic mite Varroa destructor in the transmission of slow bee paralysis virus (SBPV) was investigated. Virus transmission experiments were done in two seasons (July and September) using pupae of the honey bee, Apis mellifera and mites that had fed on SBPV-infected pupae (as the virus acquisition source or VAS) for either five or ten days (as the virus acquisition period or VAP). The doses necessary to cause 50 and 99% mortality in bees were estimated as 362 (LD50) and 2266 (LD99) particles of virus using Probit analysis. A time course of SBPV replication in pupae showed that the virus was first detected 42 hours after injection. No significant differences were found in the overall proportion of pupae that became infected when mites were permitted a VAP of five or ten days, irrespective of the season (July or September). The proportion of pupae infected with SBPV declined significantly with each mite transfer over time, with the majority of pupae becoming infected after the first few mite transfers. This strongly suggests that transmission of SBPV does occur during mite feeding. However, because SBPV is also highly virulent, killing the bee rapidly and before significant virus replication, this virus remains rare in honey bee colonies even in the presence of V. destructor.