Data from: Nosema ceranae can infect honey bee larvae and reduces subsequent adult longevity

Nosema ceranae causes a widespread disease that reduces honey bee health but is only thought to infect adult honey bees, not larvae, a critical life stage. We reared honey bee (Apis mellifera) larvae in vitro and provide the first demonstration that N. ceranae can infect larvae and decrease subsequent adult longevity. We exposed three-day-old larvae to a single dose of 40,000 (40K), 10,000 (10K), zero (control), or 40K autoclaved (control) N. ceranae spores in larval food. Spores developed intracellularly in midgut cells at the pre-pupal stage (8 days after egg hatching) of 41% of bees exposed as larvae. We counted the number of N. ceranae spores in dissected bee midguts of pre-pupae and, in a separate group, upon adult death. Pre-pupae exposed to the 10K or 40K spore treatments as larvae had significantly elevated spore counts as compared to controls. Adults exposed as larvae had significantly elevated spore counts as compared to controls. Larval spore exposure decreased longevity: a 40K treatment decreased the age by which 75% of adult bees died by 28%. Unexpectedly, the low dose (10K) led to significantly greater infection (1.3 fold more spores and 1.5 fold more infected bees) than the high dose (40K) upon adult death. Differential immune activation may be involved if the higher dose triggered a stronger larval immune response that resulted in fewer adult spores but imposed a cost, reducing lifespan. The impact of N. ceranae on honey bee larval development and the larvae of naturally infected colonies therefore deserve further study.东方蜜蜂微孢子虫（Nosema ceranae）会引发一种广泛传播的病害，削弱蜜蜂健康，但此前仅被认为只能侵染成年蜜蜂，而非蜜蜂的关键生命阶段——幼虫。我们通过体外培养西方蜜蜂（Apis mellifera）幼虫，首次证实东方蜜蜂微孢子虫能够侵染幼虫，并降低其后续成虫阶段的寿命。我们将3日龄幼虫置于幼虫饲料中，分别施加单剂量40000（4万）、10000（1万）、0（空白对照组）的东方蜜蜂微孢子虫孢子，以及4万剂量的高压灭活孢子（灭活对照组）。在41%以幼虫阶段被侵染的蜜蜂的预蛹期（卵孵化后8天），孢子在中肠细胞内完成胞内发育。我们对解剖获取的预蛹中肠统计了东方蜜蜂微孢子虫孢子载量，同时在另一组实验中，于成虫死亡后统计其孢子载量。与对照组相比，以幼虫阶段暴露于1万或4万剂量孢子的预蛹，其孢子载量显著升高；以幼虫阶段被孢子侵染的成虫，其孢子载量同样显著高于对照组。幼虫期的孢子暴露会缩短成虫寿命：4万剂量处理组中，75%成虫死亡的时间较对照组提前了28%。出乎意料的是，成虫死亡后统计发现，低剂量（1万）组的侵染程度显著高于高剂量（4万）组——孢子数量高出1.3倍，受侵染个体数高出1.5倍。若更高剂量触发了更强的幼虫免疫应答，进而导致成虫体内孢子数量减少但付出了寿命缩短的代价，则这种免疫激活差异可能参与了该现象的调控。因此，东方蜜蜂微孢子虫对蜜蜂幼虫发育的影响，以及自然侵染蜂群中的幼虫阶段，均值得进一步研究。