Abstract
Social honey bees, Apis mellifera, host a set of distinct microbiota, which is similar across the continents and various honey bee species. Some of these bacteria, such as lactobacilli, have been linked to immunity and defence against pathogens. Pathogen defence is crucial, particularly in larval stages, as many pathogens affect the brood. However, information on larval microbiota is conflicting.Seven developmental stages and drones were sampled from 3 colonies at each of the 4 geographic locations of A. mellifera carnica, and the samples were maintained separately for analysis. We analysed the variation and abundance of important bacterial groups and taxa in the collected bees.Major bacterial groups were evaluated over the entire life of honey bee individuals, where digestive tracts of same aged bees were sampled in the course of time. The results showed that the microbial tract of 6-day-old 5th instar larvae were nearly equally rich in total microbial counts per total digestive tract weight as foraging bees, showing a high percentage of various lactobacilli (Firmicutes) and Gilliamella apicola (Gammaproteobacteria 1). However, during pupation, microbial counts were significantly reduced but recovered quickly by 6 days post-emergence. Between emergence and day 6, imago reached the highest counts of Firmicutes and Gammaproteobacteria, which then gradually declined with bee age. Redundancy analysis conducted using denaturing gradient gel electrophoresis identified bacterial species that were characteristic of each developmental stage.The results suggest that 3-day 4th instar larvae contain low microbial counts that increase 2-fold by day 6 and then decrease during pupation. Microbial succession of the imago begins soon after emergence. We found that bacterial counts do not show only yearly cycles within a colony, but vary on the individual level. Sampling and pooling adult bees or 6th day larvae may lead to high errors and variability, as both of these stages may be undergoing dynamic succession.
Highlights
Honey bees are a key species for agriculture, contributing significantly to the human food supply [1]
The results showed that the microbial tract of 6-day-old 5th instar larvae were nearly rich in total microbial counts per total digestive tract weight as foraging bees, showing a high percentage of various lactobacilli (Firmicutes) and Gilliamella apicola (Gammaproteobacteria 1)
Samples of honey bees in various ontogenetic stages were acquired from 4 apiary sites within 10–100 km distance of each other (S4 Fig.), and 3 colonies from each apiary site were investigated to determine bacterial diversity
Summary
Honey bees are a key species for agriculture, contributing significantly to the human food supply [1]. Recent losses of Apis mellifera and the potential association of these declines with various infectious agents highlight the need for an increased understanding of innate bee immunity and mechanisms that help them adapt to environmental stress One of these factors may be their gut microbiota; little is known regarding the role of beneficial microbes in honey bee health [2,3]. The adult honey bee hosts up to 109 bacterial cells, consisting of 8 abundant phylotypes making up to 95% of the total bacteria that appear to be specific to social bees [6] The maintenance of this stable and distinct microbial community depends on the nutrition and social lifestyle of these insects [7,8], environment [8,9] and ontogenetic stage [5,10,11]. Many studies examining bee microbiota were related to defence against the major pathogen Paenibacillus larvae, the causative agent of American foulbrood [10]
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