Behaviour, Ecology and Evolution (BEE) Laboratory, School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW, Australia.
Wageningen University and Research, Wageningen, The Netherlands.
J Anim Ecol. 2021 Oct;90(10):2254-2267. doi: 10.1111/1365-2656.13493. Epub 2021 May 12.
Global pollinator declines as a result of emerging infectious diseases are of major concern. Managed honeybees Apis mellifera are susceptible to numerous parasites and pathogens, many of which appear to be transmissible to sympatric non-Apis taxa. The ectoparasitic mite Varroa destructor is considered to be the most significant threat to honeybees due to its role in vectoring RNA viruses, particularly Deformed wing virus (DWV). Vector transmission of DWV has resulted in the accumulation of high viral loads in honeybees and is often associated with colony death. DWV has two main genotypes, A and B. DWV-A was more prevalent during the initial phase of V. destructor establishment. In recent years, the global prevalence of DWV-B has increased, suggesting that DWV-B is better adapted to vector transmission than DWV-A. We aimed to determine the role vector transmission plays in DWV genotype prevalence at a colony level. We experimentally increased or decreased the number of V. destructor mites in honeybee colonies, and tracked DWV-A and DWV-B loads over a period of 10 months. Our results show that the two DWV genotypes differ in their response to mite numbers. DWV-A accumulation in honeybees was positively correlated with mite numbers yet DWV-A was largely undetected in the absence of the mite. In contrast, colonies had high loads of DWV-B even when mite numbers were low. DWV-B loads persisted in miticide-treated colonies, indicating that this genotype has a competitive advantage over DWV-A irrespective of mite numbers. Our findings suggest that the global increase in DWV-B prevalence is not driven by selective pressure by the vector. Rather, DWV-B is able to persist in colonies at higher viral loads relative to DWV-A in the presence and absence of V. destructor. The interplay between V. destructor and DWV genotypes within honeybee colonies may have broad consequences upon viral diversity in sympatric taxa as a result of spillover.
由于新发传染病的出现，全球传粉媒介数量下降令人担忧。人工饲养的蜜蜂（Apis mellifera）易受多种寄生虫和病原体的影响，其中许多似乎可以传播给共生的非 Apis 类群。外寄生螨 Varroa destructor 被认为是对蜜蜂的最大威胁，因为它在传播 RNA 病毒方面发挥了作用，特别是变形翅膀病毒（DWV）。DWV 通过媒介传播，导致蜜蜂体内积累了高病毒载量，并且经常与蜂群死亡有关。DWV 有两个主要基因型，A 和 B。在 Varroa destructor 建立的初始阶段，DWV-A 更为普遍。近年来，DWV-B 在全球的流行率有所增加，这表明 DWV-B 比 DWV-A 更适应媒介传播。我们旨在确定媒介传播在蜂群水平上对 DWV 基因型流行率的作用。我们通过实验增加或减少蜜蜂群中的 Varroa destructor 螨的数量，并在 10 个月的时间内跟踪 DWV-A 和 DWV-B 的负载。我们的研究结果表明，这两种 DWV 基因型对螨数量的反应不同。在蜜蜂中，DWV-A 的积累与螨的数量呈正相关，但在没有螨的情况下，DWV-A 则大部分未被检测到。相比之下，即使螨的数量很低，蜂群中也会有大量的 DWV-B。在使用杀螨剂处理的蜂群中，DWV-B 的负载仍然存在，这表明无论螨的数量如何，该基因型相对于 DWV-A 都具有竞争优势。我们的研究结果表明，全球范围内 DWV-B 流行率的增加不是由媒介的选择压力驱动的。相反，与 DWV-A 相比，在有或没有 Varroa destructor 的情况下，DWV-B 能够在更高的病毒载量下在蜂群中持续存在。由于溢出效应，Varroa destructor 和 DWV 基因型之间在蜜蜂群中的相互作用可能会对共生类群中的病毒多样性产生广泛的影响。
