Abstract
Varroa destructor mites express strong avoidance of the Apis cerana worker brood in the field. The molecular mechanism for this phenomenon remains unknown. We identified a Varroa toxic protein (VTP), which exhibited toxic activity toward A. cerana worker larvae, in the saliva of these mites, and expressed VTP in an Escherichia coli system. We further demonstrated that recombinant VTP killed A. cerana worker larvae and pupae in the absence of deformed-wing virus (DWV) but was not toxic to A. cerana worker adults and drones. The recombinant VTP was safe for A. mellifera individuals, but resulted in elevated DWV titers and the subsequent development of deformed-wing adults. RNAi-mediated suppression of vtp gene expression in the mites partially protected A. cerana larvae. We propose a modified mechanism for Varroa mite avoidance of worker brood, due to mutual destruction stress, including the worker larvae blocking Varroa mite reproduction and Varroa mites killing worker larvae by the saliva toxin. The discovery of VTP should provide a better understanding of Varroa pathogenesis, facilitate host-parasite mechanism research and allow the development of effective methods to control these harmful mites.
Highlights
The balanced relationship between the original host A. cerana and V. destructor is the most striking aspect of this ectoparasite
We injected crude saliva collected from female Varroa mites into A. cerana and A. mellifera larvae and observed that this treatment killed A. cerana worker larvae, while injected A. mellifera larvae developed into adults with deformed wings
We detected deformed wing virus [deformed-wing virus (DWV)] in A. mellifera larvae, pupae and adult workers and drones, Varroa mites and their saliva, and A. cerana infested with mites or injected with mite saliva but not in A. cerana that were injected or not injected with E-Varroa saliva toxic protein (VTP) (E-VTP = the expressed VTP fused with an epitope tag) (Supplementary Table S1)
Summary
The balanced relationship between the original host A. cerana and V. destructor is the most striking aspect of this ectoparasite. Varroa mites show a marked preference for the drone brood and a strong avoidance of the worker brood in A. cerana colonies[4,13]. Based on the secretome results, we identified a Varroa saliva toxic protein (VTP) that exhibited toxic activity towards A. cerana worker larvae from freshly capped cells in the absence of DWV and Guangdong Public Laboratory of Wild Animal Conservation and Utilization, Guangdong Key Laboratory of Animal Protection and Resource Utilization, Guangdong Institute of Applied Biological Resources, 105 Xingang Road West, Guangzhou, 510260, China. The discovery of VTP should help elucidate the interaction mechanism between the host and parasite and allow the development of effective anti-mite methods, based on RNAi-mediated and/or gene-editing knockdown of vtp receptor genes, for protecting A. mellifera colonies
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
