Spatial distribution of recapping behaviour indicates clustering around Varroa infested cells

<i>Varroa destructor</i> is arguably the most important threat to <i>Apis mellifera</i> honey bees. Despite the recentness of the invasion of Varroa, <i>A. mellifera</i> colonies naturally resistant to the mite are being observed in a growing number of populations across Europe, South Africa and Brazil. Appearing in concert with this resistance is an increase in the ability of workers to detect mite-infested cells, which is closely associated with the recapping of such cells. However, many non-infested cells are also uncapped and then recapped which would appear to be a waste of time and energy. In this study we looked at the spatial patterns of recapping and its association with Varroa infestation to understand in what way the uncapping of non-infested cells occurs. We found that recapping occurred in clusters consisting of infested cells and their surrounding non-infested cells. This helped explain our finding that a significant positive correlation existed between levels of recapped infested and non-infested cells. Furthermore, we found that bees responded to an artificial increase in the mite infestation level by increasing their recapping behavior. We confirmed that the recapped area of non-infested cells was significantly smaller, relative to the holes made in the infested cells. Given these findings we propose that recapping behavior is stimulated either by a diffuse signal emanating from the infested cell or that cursory checks are conducted in the vicinity of an infested cell.

瓦螨（Varroa destructor）无疑是西方蜜蜂（Apis mellifera）所面临的最具危害性的威胁。尽管该螨的入侵时间尚短，但在欧洲、南非与巴西的多个种群中，越来越多对该螨具有天然抗性的西方蜜蜂蜂群已被观测到。与这种抗性相伴出现的，是工蜂检测螨类侵染封盖细胞的能力显著提升，这一能力与此类封盖细胞的复盖（recapping）行为密切相关。然而，大量未被侵染的封盖细胞也会被开盖（uncapping）后再进行复盖，这看似是对时间与能量的无谓浪费。本研究聚焦复盖行为的空间分布模式及其与瓦螨侵染的关联，以探明未侵染封盖细胞开盖行为的发生机制。研究发现，复盖行为集中发生于被侵染细胞及其周边未侵染细胞构成的集群中，这一结果也解释了为何我们观测到复盖的被侵染细胞与未侵染细胞的数量间存在显著正相关关系。此外，我们发现蜂群会通过增强复盖行为，对人工提升的螨类侵染水平作出响应。我们还证实，相较于被侵染细胞上形成的孔洞，未侵染细胞的复盖面积显著更小。基于上述发现，我们提出复盖行为的触发存在两种可能：要么源自被侵染细胞释放的弥散信号，要么是蜂群会在被侵染细胞周边开展粗略检查。