Israeli acute paralysis virus (IAPV) is a widespread RNA virus of honey bees that has been linked with colony losses. Here we describe the transmission, prevalence, and genetic traits of this virus, along with host transcriptional responses to infections. Further, we present RNAi-based strategies for limiting an important mechanism used by IAPV to subvert host defenses. Our study shows that IAPV is established as a persistent infection in honey bee populations, likely enabled by both horizontal and vertical transmission pathways. The phenotypic differences in pathology among different strains of IAPV found globally may be due to high levels of standing genetic variation. Microarray profiles of host responses to IAPV infection revealed that mitochondrial function is the most significantly affected biological process, suggesting that viral infection causes significant disturbance in energy-related host processes. The expression of genes involved in immune pathways in adult bees indicates that IAPV infection triggers active immune responses. The evidence that silencing an IAPV-encoded putative suppressor of RNAi reduces IAPV replication suggests a functional assignment for a particular genomic region of IAPV and closely related viruses from the Family Dicistroviridae, and indicates a novel therapeutic strategy for limiting multiple honey bee viruses simultaneously and reducing colony losses due to viral diseases. We believe that the knowledge and insights gained from this study will provide a new platform for continuing studies of the IAPV–host interactions and have positive implications for disease management that will lead to mitigation of escalating honey bee colony losses worldwide.

Graphical abstract

-The ability of the parasitic mite Varroa destructor to transmit Kashmir bee virus (KBV) to the Western honey bee (Apis mellifera) was investigated by exposing pupae from a KBV-negative colony to varying numbers of adult female mites from KBV-positive colonies. After five days, the virus status of pupae and the mites was determined by RT-PCR. There was a significant relationship between KBVpositive pupae and exposure to KBV-positive mites. No pupae were virus-positive when all the mites introduced into a given cell subsequently tested negative. Mites testing positive for KBV transmitted virus about 70% of the time. The percentage of KBV-positive V. destructor in a given cell also increased significantly, suggesting virus-free mites became virus-positive by cohabiting in the same cell with viruspositive mites, and we calculated the mite-to-mite transmission rate as 51%. There was 100% sequence identity of 415 bp KBV fragment amplified from bee pupae and mites, reflecting two isolates of the same virus source and supporting the conclusion of virus transmission from mite to bee pupae. Kashmir bee virus / transmission / Varroa destructor / RT-PCR