Discovery Of Two New Virus Strains Of Varroa Destructor And Their Infectivity To Honeybee

Varroa destructor is an ectoparasite of honeybee.It feeds on the fat body and hemolymph of honeybee,and carries and spreads bee viruses in the colony,thus provides favorable conditions for the inter-species transmission of V.destructor viruses and the outbreak of new infectious diseases of honeybee.Most V.destructor viruses are RNA viruses with high mutation and strong adaptability.Among them,VDV-1 has been proved to have a strong pathogenicity to honeybee.However,there are only a few studies on the infectivity and pathogenicity of other V.destructor viruses on honeybee.In order to increase the understanding of V.destructor viruses and their possible effects on honeybee and lay a theoretical foundation for the assessment of the potential risk of V.destructor viruses on the health of honeybee,this study focused on RNA virus of V.destructor in China.The main contents and results of this study are as follows:(1)RNA sequencing of V.destructor infecting Apis cerana and Apis mellifera in China was conducted to detect common RNA viruses and discover new viruses.The results indicated that DWV,SBV,BQCV,and IAPV existed in V.destructor from A.mellifera and A.cerana.And we also detected VDV-1 and VDV-2 for the first time in V.destructor in China.In addition,we found two sets of unknown RNA virus sequences with high abundance in the sequencing data of all the V.destructor samples.One of them is 79%similar to Varroa destructor virus 2(VDV-2)and named as Varroa destructor virus 2 China(VDV-2 CHN),The amino acid sequence of the other one is 32%similar to the amino acid sequence of the capsid protein of Beihai horseshoe crab virus 1 and named as Varroa destructor virus 6(VDV-6).(2)RT-PCR was used to detected VDV-2 CHN and VDV-6 in V.destructor from Zhejiang and Yunnan and in adult workers of A.mellifera and A.cerana from Gansu,Mubei,Jiangxi,Zhejiang,Guangdong,Yunnan.Tagged RT-PCR was used to study the infrectivity of the two viruses to honeybee under natural conditions.Our results showed that VDV-2 CHN and VDV-6 were widely prevalent in V.destructor from A.mellifera and A.cerana,but in honeybee samples,they only existed in a part of A.mellifera worker pupae that parasitized by many V.destructor and complementary strands of these viruses were only detected in V.destructor.(3)The results of qPCR and Tagged RT-PCR on adult workers inoculated orally with VDV-2 CHN and VDV-6 indicated that VDV-2 CHN and VDV-6 could replicate slightly in adult workers of A.mellifera and A.cerana under the condition of artificial oral inoculation with high titer virus.In conclusion,two RNA virus strains VDV-2 CHN and VDV-6 were discovered in V.destructor.These two virus strains did not show infectivity to honeybee under natural conditions,while under the condition of artificial oral inoculation with high titer virus,they had certain infectivity to adult worker bees of A.mellifera and A.cerana.The results of this study suggested that these two new V.destructor virus strains might spread to honeybees via inter-species transmission.