Center for Social Evolution, Department of Agriculture and Ecology, University of Copenhagen, Thorvaldsensvej 40, DK 1871 Frederiksberg C, Denmark.
Vet Microbiol. 2011 Apr 21;149(1-2):200-5. doi: 10.1016/j.vetmic.2010.10.001. Epub 2010 Oct 8.
Chalkbrood (Ascosphaera apis) and stonebrood (Aspergillus flavus) are well known fungal brood diseases of honeybees (Apis mellifera), but they have hardly been systematically studied because the difficulty of rearing larvae in vitro has precluded controlled experimentation. Chalkbrood is a chronic honeybee-specific disease that can persist in colonies for years, reducing both brood and honey production, whereas stonebrood is a rare facultative pathogen that also affects hosts other than honeybees and can likely survive outside insect hosts. Hive infection trials have indicated that accidental drops in comb temperature increase the prevalence of chalkbrood, but it has remained unclear whether virulence is directly temperature-dependent. We used a newly established in vitro rearing technique for honeybee larvae to test whether there are systematic temperature effects on mortality induced by controlled infections, and whether such effects differed between the two fungal pathogens. We found that increasing spore dosage at infection had a more dramatic effect on mortality from stonebrood compared to chalkbrood. In addition, a 24h cooling period after inoculation increased larval mortality from chalkbrood infection, whereas such a cooling period decreased mortality after stonebrood infection. These results raise interesting questions about honeybee defenses against obligate and facultative pathogens and about the extent to which stress factors in the host (dis)favor pathogens with lesser degrees of specialization.
粉孢子病（Ascosphaera apis）和石孢子病（Aspergillus flavus）是众所周知的蜜蜂（Apis mellifera）真菌幼虫病，但由于体外幼虫饲养的难度阻碍了控制实验，它们几乎没有得到系统研究。粉孢子病是一种慢性的蜜蜂特异性疾病，它可以在蜂群中持续多年，减少幼虫和蜂蜜的产量，而石孢子病是一种罕见的兼性病原体，也会影响除蜜蜂以外的宿主，并且很可能在昆虫宿主之外存活。蜂箱感染试验表明，巢房温度的意外下降会增加粉孢子病的流行，但仍然不清楚毒力是否直接受温度影响。我们使用新建立的蜜蜂幼虫体外饲养技术来测试受控感染引起的死亡率是否存在系统的温度效应，以及这种效应是否在两种真菌病原体之间存在差异。我们发现，在感染时增加孢子剂量对石孢子病引起的死亡率有更显著的影响，而对粉孢子病的影响较小。此外，接种后 24 小时的冷却期会增加粉孢子病感染引起的幼虫死亡率，而在石孢子病感染后，这种冷却期会降低死亡率。这些结果提出了一些有趣的问题，即蜜蜂对专性和兼性病原体的防御能力，以及宿主中的应激因素在多大程度上有利于专业化程度较低的病原体。
