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）可引发一种广泛传播的病害，削弱蜜蜂健康，但此前仅被认为会侵染成年蜜蜂，而非其关键生命阶段的幼虫。本研究通过体外培养西方蜜蜂（Apis mellifera）幼虫，首次证实该病原可侵染幼虫，并降低其后羽化的成年蜜蜂的寿命。我们将3日龄幼虫置于添加了不同剂量东方蜜蜂微孢子虫孢子的幼虫饲料中进行暴露处理，剂量分别为单次40000（4万）、10000（1万）、0（对照组），以及经高压灭菌的4万孢子（灭活对照组）。在以幼虫阶段暴露处理的蜜蜂中，有41%的个体在预蛹期（卵孵化后8天）于中肠细胞内形成胞内发育的孢子。我们分别统计了预蛹期解剖的蜜蜂中肠内的东方蜜蜂微孢子虫孢子数量，以及另一独立实验组中成年蜜蜂死亡后的中肠孢子载荷。以幼虫阶段暴露于1万或4万孢子剂量组的预蛹，其孢子数量显著高于对照组。以幼虫阶段接受暴露处理的成年蜜蜂，其孢子载荷同样显著高于对照组。幼虫阶段的孢子暴露会缩短成虫寿命：4万剂量组中，75%成年蜜蜂的死亡日龄较对照组降低了28%。值得注意的是，成年蜜蜂死亡后检测发现，低剂量组（1万）的侵染程度显著高于高剂量组（4万）：孢子数量高出1.3倍，受侵染个体比例高出1.5倍。该现象可能与免疫激活差异相关：高剂量孢子暴露或许触发了更强的幼虫免疫应答，虽可减少成虫阶段的孢子载荷，但同时带来了寿命缩短的代价。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带菌情况，均有待进一步研究。