Dynamics of Apis cerana Sacbrood Virus (AcSBV) Prevalence in Apis cerana (Hymenoptera: Apidae) in Northern Taiwan and Demonstration of its Infection in Apis mellifera (Hymenoptera: Apidae)

Abstract

Since 2016, Apis cerana sacbrood virus (AcSBV) has been recorded in Taiwan. It is epizootic in Apis cerana (Hymenoptera: Apidae) and causing serious loss of A. cerana. Herein, we performed a long-term survey of AcSBV prevalence in the populations of A. cerana in Northern Taiwan from January 2017 to July 2018. The surveillance of AcSBV prevalence in A. mellifera (Hymenoptera: Apidae) populations was starting and further confirmed by sequencing since April 2017; thus, these data were also included in this survey. In our survey, the average prevalence rates of AcSBV were 72 and 53% in A. cerana and A. mellifera, respectively, in 2017, which decreased to 45 and 27% in 2018. For the spatial analysis of AcSBV in two honey bee populations, Hsinchu showed the highest prevalence, followed by New Taipei, Yilan, Taipei, and Keelung, suggesting that AcSBV might have come from the southern part of Taiwan. Interestingly, the AcSBV prevalence rates from A. cerana and A. mellifera cocultured apiaries gradually synchronized. The result of phylogenetic analysis and comparison of the annual AcSBV prevalence in A. cerana-only, A. mellifera-only, and A. cerana/A. mellifera cocultured sample sites indicate cross-infection between A. cerana and A. mellifera; however, AcSBV may lose the advantage of virulence in A. mellifera. The evidence suggested that the transmission of AcSBV might occur among these two honey bee species in the field. Therefore, A. mellifera may serve as a guard species to monitor AcSBV in A. cerana, but the cross-infection still needs to be surveyed.

Genomic Sequencing and Comparison of Sacbrood Viruses from Apis cerana and Apis mellifera in Taiwan

“…In Taiwan, most A. cerana populations are reared in Northern Taiwan, and according to our observations, some of these apiaries are crossbreeding with A. mellifera populations. The detection of AcSBV prevalence in A. mellifera populations from the sampling sites where A. cerana and A. mellifera were crossbreeding confirmed that AcSBV prevalence rates gradually developed a similar trend in the A. cerana and A. mellifera crossbreeding apiaries, and the existence of AcSBV cross-infection between A. cerana and A. mellifera was also confirmed by phylogenetic analysis based on partial VP1 sequences [33]. Similar to our case, some SBV strains from A. mellifera included in this study were found to be distinct from other AmSBV strains in terms of genomic features and were clustered with AcSBVs based on whole genome comparisons and phylogenetic analysis [24,30,36,40].…”

“…AcSBV has recently been recorded in Taiwan and caused serious losses of A. cerana from 2015 to 2019 [33][34][35]. In Taiwan, most A. cerana populations are reared in Northern Taiwan, and according to our observations, some of these apiaries are crossbreeding with A. mellifera populations.…”

“…The whole genomes of SBV strains from A. mellifera and A. cerana were determined, and the origin of AcSBV-TW was indicated to be close to China, while AmSBV-TW presented novel genomic features. The cross-infection of A. mellifera with AcSBV was demonstrated in the apiaries, where A. mellifera and A. cerana were crossbreeding in Northern Taiwan in our previous report [33], suggesting that the variations identified in the genomes of AcSBV-TW and AmSBV-TW. According to the whole genome data, the sequences of 5 and 3 UTR revealed divergence compared to the polyprotein coding sequences either between AcSBV-TW and AmSBV-TW or among those of SBV from other countries, assuming there is less evolutionary pressure on the untranslated regions of the viral genomes.…”

“…These reports identified different genomic features and revealed the genetic diversity among these SBVs, suggesting that viral cross-infections might occur between AcSBV and AmSBV. According to our previous data, cross-infection might occur between AcSBV and AmSBV in Taiwan [33,35]. However, the available information on the whole genome sequences of AcSBV and AmSBV in Taiwan is insufficient.…”

“…The A. cerana has a higher tolerance for low tempera-Pathogens 2021, 10, 14 2 of 18 ture and better performance on the pollination in the mountain regions than A. mellifera. Therefore, A. cerana contributes to the pollination of mountainous orchards, including plums and peaches, etc., which are counted for 1.3% of Taiwan agricultural production [33]. Since AcSBV was first detected in Taiwan in 2015, many beekeepers in Taiwan have reported significant A. cerana larval death with symptoms caused by AcSBV in A. cerana colonies [34,35].…”