The trypanosomatids Crithidia mellificae and Lotmaria passim are very prevalent in honey bee colonies and potentially contribute to colony losses that currently represent a serious threat to honey bees. However, potential pathogenicity of these trypanosomatids remains unclear and since studies of infection are scarce, there is little information about the virulence of their different morphotypes. Hence, we first cultured C. mellificae and L. passim (ATCC reference strains) in six different culture media to analyse their growth rates and to obtain potentially infective morphotypes. Both C. mellificae and L. passim grew in five of the media tested, with the exception of M199. These trypanosomatids multiplied fastest in BHI medium, in which they reached a stationary phase after around 96 h of growth. Honey bees inoculated with either Crithidia or Lotmaria died faster than control bees and their mortality was highest when they were inoculated with 96 h cultured L. passim. Histological and Electron Microscopy analyses revealed flagellated morphotypes of Crithidia and Lotmaria in the lumen of the ileum, and adherent non-flagellated L. passim morphotypes covering the epithelium, although no lesions were evident. These data indicate that parasitic forms of these trypanosomatids obtained from the early stationary growth phase infect honey bees. Therefore, efficient infection can be achieved to study their intra-host development and to assess the potential pathogenicity of these trypanosomatids.

锥虫Crithidia melificae和Lotmaria passim在蜜蜂群中非常普遍，并可能导致目前对蜜蜂构成严重威胁的群落损失。然而，这些锥虫的潜在致病性仍不清楚，而且由于对感染的研究很少，关于它们不同形态型毒力的信息很少。因此，我们首先在六种不同的培养基中培养C. melificae和L. passim（ATCC 参考菌株）以分析它们的生长速率并获得潜在的感染性形态类型。无论C. mellificae和L.各处除 M199 外，在五种测试介质中均有所增长。这些锥虫在 BHI 培养基中繁殖最快，在生长约 96 小时后达到稳定期。接种Crithidia或Lotmaria 的蜜蜂比对照蜜蜂死亡得更快，并且当它们接种 96 小时培养的L. passim时，它们的死亡率最高。组织学和电子显微镜分析揭示了回肠腔中Crithidia和Lotmaria 的鞭毛形态型，以及粘附的非鞭毛L. passim覆盖上皮的形态类型，尽管没有明显的病变。这些数据表明，从早期稳定生长期获得的这些锥虫的寄生形式会感染蜜蜂。因此，可以实现有效的感染来研究它们的宿主内发育并评估这些锥虫的潜在致病性。