Influence of Age of Infection on the Gut Microbiota in Worker Honey Bees (Apis mellifera iberiensis) Experimentally Infected with Nosema ceranae

The gut microbiota of honey bees has received increasing interest in the past decades due to its crucial role in their health, and can be disrupted by pathogen infection. Nosema ceranae is an intracellular parasite that affects the epithelial cells of the midgut, altering gut homeostasis and representing a major threat to honey bees. Previous studies indicated that younger worker bees are more susceptible to experimental infection by this parasite, although the impact of infection and of age on the gut bacterial communities remains unclear. To address this, honey bees were experimentally infected with a consistent number of N. ceranae spores at various ages post-emergence (p.e.) and the gut bacteria 7 days post-infection (p.i.) were analysed using real-time quantitative PCR, with the results compared to non-infected controls. Infected bees had a significantly higher proportion and load of Gilliamella apicola. In respect to the age of infection, the bees infected just after emergence had elevated loads of G. apicola, Bifidobacterium asteroides, Bombilactobacillus spp., Lactobacillus spp., Bartonella apis, and Bombella apis. Moreover, the G. apicola load was higher in bees infected at nearly all ages, whereas older non-infected bees had higher loads of Bifidobacterium asteroides, Bombilactobacillus spp., Lactobacillus spp., Ba. apis, and Bo apis. These findings suggest that N. ceranae infection and, in particular, the age of bees at infection modulate the gut bacterial community, with G. apicola being the most severely affected species.

Frequent Parasitism of Apis mellifera by Trypanosomatids in Geographically Isolated Areas with Restricted Beekeeping Movements

Trypanosomatids form a group of high prevalence protozoa that parasitise honey bees, with Lotmaria passim as the predominant species worldwide. However, the knowledge about the ecology of trypanosomatids in isolated areas is limited. The Portuguese archipelagos of Madeira and Azores provide an interesting setting to investigate these parasites because of their geographic isolation, and because they harbour honey bee populations devoid of two major enemies: Varroa destructor and Nosema ceranae. Hence, a total of 661 honey bee colonies from Madeira and the Azores were analysed using different molecular techniques, through which we found a high prevalence of trypanosomatids despite the isolation of these islands. L. passim was the predominant species and, in most colonies, was the only one found, even on islands free of V. destructor and/or N. ceranae with severe restrictions on colony movements to prevent the spread of them. However, islands with V. destructor had a significantly higher prevalence of L. passim and, conversely, islands with N. ceranae did not shown any significant correlation with the trypanosomatid. Crithidia bombi was detected in Madeira and on three islands of the Azores, almost always coincident with L. passim. By contrast, Crithidia mellificae was not detected in any sample. A high-throughput sequencing analysis distinguished two main haplotypes of L. passim, which accounted for 98% of the total sequence reads. This work suggests that L. passim and C. bombi are parasites that have been associated with honey bees predating the spread of V. destructor and N. ceranae.