Spatial distribution of recapping behaviour indicates clustering around Varroa infested cells

Varroa destructor is arguably the most important threat to Apis mellifera honey bees. Despite the recentness of the invasion of Varroa, A. mellifera 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）面临的最严峻威胁。尽管瓦螨的入侵历史尚短，但在欧洲、南非与巴西的越来越多的蜂群种群中，已观测到对该螨具有天然抗性的西方蜜蜂蜂群。与这种抗性相伴出现的，是工蜂识别受螨寄生巢房的能力提升，而该能力与这类巢房的重新封盖行为密切相关。然而，许多未受寄生的巢房也会被开盖后重新封盖，这看似是对时间与精力的无谓消耗。本研究聚焦于重新封盖行为的空间分布模式，及其与瓦螨寄生情况的关联，以探明未受寄生巢房的开盖行为发生机制。我们发现，重新封盖行为以集群形式出现，集群既包含受寄生巢房，也包括其周边的未受寄生巢房。这一结果解释了我们的观测发现：受寄生巢房与未受寄生巢房的重新封盖水平之间存在显著正相关。此外，我们发现蜂群会通过提升重新封盖行为的强度，对人工提高的螨寄生水平做出响应。我们还证实，相较于受寄生巢房上的开孔面积，未受寄生巢房的重新封盖区域显著更小。基于上述发现，我们提出两种推测：重新封盖行为可能由受寄生巢房释放的弥散信号所激发，或是蜂群会在受寄生巢房周边开展粗略检查。