|De Guzman, Lilia|
Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2014
Publication Date: N/A
Citation: Interpretive Summary: Apis mellifera colonies are commonly infested with two genera of mites (Varroa spp. and Tropilaelaps spp.) in Asia. However, Tropilaelaps mites are considered to be the major health threat. The feeding activities of mites and the presence of viruses they vector may trigger immune responses in honey bees. This study measured the expression levels of four immunity-related genes (abaecin, apidaecin, hymenoptaecin and eater), and incidence of different honey bee viruses as influenced by the number of actively feeding T. mercedesae. Our results showed that apidaecin and eater had differences in expression levels while no expression differences were detected for abaecin and hymenoptaecin. A large percentage of the pupae were infected with Deformed wing virus (DWV) and Black queen cell virus (BQCV). The occurrence of DWV in pupae was related to a positive DWV infection status of the mites. Also, the presence of variable levels of DWV and low levels of BQCV did not support any expression differences for any of the immunity genes. Acute bee paralysis virus, Kashmir bee virus and Sacbrood virus were not detected. This study shows that Tropilaelaps parasitism produced an immune response but the level of viruses did not produce a correlated immune response by the four genes tested. Also, Tropilaelaps vectored viruses but not to a high degree. Hence, the major impact of Tropilaelaps infestation is caused by the mite itself.
Technical Abstract: Tropilaelaps mites are the major health threat to Apis mellifera colonies in Asia because of their widespread occurrence, rapid population growth and potential ability to transfer bee viruses. Honey bee immune responses in the presence of feeding mites may occur in response to mite feeding, to the presence of viruses or to both. In this study, the mRNA expression levels were measured for three antimicrobial peptide encoding genes (abaecin, apidaecin, hymenoptaecin) and a phagocytosis receptor gene (eater) in worker brood infested with different numbers of actively feeding T. mercedesae. Also, all samples were measured for the amount of Acute bee paralysis virus (ABPV), Black queen cell virus (BQCV), Deformed wing virus (DWV), Kashmir bee virus (KBV) and Sacbrood virus (SBV). Analysis showed that apidaecin was significantly down-regulated when tan-bodied pupae were infested with 1-2 mites and when capping of the cells of newly sealed larvae were opened and closed without mite inoculation (o/c) as compared to the control group (undisturbed brood, no mite inoculation). Reduced transcription levels of the eater gene were also recorded in the o/c group. However, an up-regulation of apidaecin and eater genes was observed in highly infested pupae when compared to o/c group. This occurrence is perhaps due to an adaptive response of the bees to higher mite infestations by up-regulating their immune expression. No significant expression differences were detected for abaecin and hymenoptaecin. ABPV, KBV and SBV were not detected. However, 86.7% of the pupae were infected with DWV, 83.3% were infected with BQCV and 73% were infected by both of these viruses. The presence of these two honey bee viruses was not related to the number of T. mercedesae infecting the pupae. But, the occurrence of DWV in pupae was related to a positive DWV infection status of the mites. Also, the presence of variable levels of DWV and low levels of BQCV did not provoke any expression differences for any of the targeted genes. Overall, this research indicates that that Tropilaelaps mite feeding produced an immune response, that the level of viruses did not produce a correlated immune response by the four genes tested and that Tropilaelaps did vector viruses but not to a high degree. Clearly, the major impact of Tropilaelaps infestation is caused by the mite itself.