Data from: A test of the invasive pathogen hypothesis of bumble bee decline in North America

Emergent fungal diseases are critical factors in global biodiversity declines. The fungal pathogenNosema bombiwas recently found to be widespread in declining species of North American bumble bees (Bombus), with circumstantial evidence suggesting an exotic introduction from Europe. This interpretation has been hampered by a lack of knowledge of global genetic variation, geographic origin, and changing prevalence patterns ofN. bombiin declining North American populations. Thus, the temporal and spatial emergence ofN. bombiand its potential role in bumble bee decline remain speculative. We analyzeNosemaprevalence and genetic variation in the United States and Europe from 1980, before an alleged introduction in the early 1990s, to 2011, extractingNosemaDNA fromBombusnatural history collection specimens from across this time period.Nosema bombiprevalence increased significantly from low detectable frequency in the 1980s to significantly higher frequency in the mid- to late-1990s, corresponding to a period of reported massive infectious outbreak ofN. bombiin commercial bumble bee rearing stocks in North America. Despite the increased frequency, we find no conclusive evidence of an exoticN. bombiorigin based on genetic analysis of globalNosemapopulations; the widespreadNosemastrain found currently in declining United States bumble bees was present in the United States before commercial colony trade. Notably, the USN. bombiis not detectably different from that found predominantly throughout Western Europe, with both regions characterized by low genetic diversity compared with high levels of diversity found in Asia, where commercial bee breeding activities are low or nonexistent.

新发真菌病害是全球生物多样性下降的关键影响因子。近日研究人员在北美数量下降的熊蜂属（Bombus）物种中广泛检出真菌病原体熊蜂微孢子虫（Nosema bombi），并有间接证据表明该病原体为欧洲传入的外来物种。这一推论因缺乏对全球范围内该病原体的遗传变异、地理起源，以及北美下降种群中N. bombi流行模式变化的认知而受限。因此，N. bombi的时空暴发特征及其在熊蜂种群下降中扮演的潜在作用仍属推测范畴。本研究分析了1980年（据称1990年代初传入之前）至2011年间美国与欧洲的Nosema属流行率及遗传变异情况，通过提取该时段内熊蜂属自然历史馆藏标本中的Nosema属DNA完成相关分析。研究结果显示，N. bombi的流行率从1980年代可检出的低水平显著升高至1990年代中后期的较高水平，这一时间节点与北美商业熊蜂饲养种群中大规模爆发N. bombi感染的公开报道相吻合。尽管流行率有所上升，但基于全球Nosema种群的遗传分析，我们并未找到该病原体为外来入侵菌株的确凿证据；当前美国下降熊蜂种群中检出的广泛分布的Nosema菌株，早在商业蜂群贸易开展前就已存在于美国境内。值得注意的是，美国的N. bombi与西欧主流菌株无显著遗传差异；与亚洲地区较高的遗传多样性水平相比，欧美两地的遗传多样性均处于较低水平，而亚洲的商业蜜蜂繁育活动规模较小或根本不存在。