The role of a balanced gut microbiota to maintain health and prevent diseases is largely established in humans and livestock. Conversely, in honeybees, studies on gut microbiota perturbations by external factors have started only recently. Natural methods alternative to chemical products to preserve honeybee health have been proposed, but their effect on the gut microbiota has not been examined in detail. This study aims to investigate the effect of the administration of a bacterial mixture of bifidobacteria and Lactobacillaceae and a commercial product HiveAliveTM on honeybee gut microbiota. The study was developed in 18 hives of about 2500 bees, with six replicates for each experimental condition for a total of three experimental groups. The absolute abundance of main microbial taxa was studied using qPCR and NGS. The results showed that the majority of the administered strains were detected in the gut. On the whole, great perturbations upon the administration of the bacterial mixture and the plant-based commercial product were not observed in the gut microbiota. Significant variations with respect to the untreated control were only observed for Snodgrassella sp. for the bacterial mixture, Bartonella sp. in HiveAliveTM and Bombilactobacillus sp. for both. Therefore, the studied approaches are respectful of the honeybee microbiota composition, conceivably without compromising the bee nutritional, social and ecological functions.

Nosema ceranae is a major pathogen in the beekeeping sector, responsible for nosemosis. This disease is hard to manage since its symptomatology is masked until a strong collapse of the colony population occurs. Conversely, no medicaments are available in the market to counteract nosemosis, and only a few feed additives, with claimed antifungal action, are available. New solutions are strongly required, especially based on natural methods alternative to veterinary drugs that might develop resistance or strongly pollute honey bees and the environment. This study aims at investigating the nosemosis antiparasitic potential of some plant extracts, microbial fermentation products, organic acids, food chain waste products, bacteriocins, and fungi. Honey bees were singularly infected with 5 × 104 freshly prepared N. ceranae spores, reared in cages and fed ad libitum with sugar syrup solution containing the active ingredient. N. ceranae in the gut of honey bees was estimated using qPCR. The results showed that some of the ingredients administered, such as acetic acid at high concentration, p-coumaric acid, and Saccharomyces sp. strain KIA1, were effective in the control of nosemosis. On the other hand, wine acetic acid strongly increased the N. ceranae amount. This study investigates the possibility of using compounds such as organic acids or biological agents including those at the base of the circular economy, i.e., wine waste production, in order to improve honeybee health.

This study investigates the impact of the three most widely used antibiotics in the beekeeping sector (oxytetracycline, tylosin, and sulfonamides) on the honeybee gut microbiota and on the spread of antibiotic resistance genes. The research represents an advance to the present literature, considering that the tylosin and sulfonamides effects on the gut microbiota have never been studied.

Several studies have outlined that a balanced gut microbiota offers metabolic and protective functions supporting honeybee health and performances. The present work contributes to increasing knowledge on the impact on the honeybee gut microbiota of the administration of three different veterinary drugs (oxytetracicline, sulphonamides and tylosin). The trial was designed with a semi-field approach in micro-hives containing about 500 bees, i.e. in experimental conditions as close as possible to real hives considering the restrictions on the use of antibiotics; 6 replicates were considered for each treatment plus the control. The absolute abundance of the major gut microbial taxa in newly eclosed individuals was studied with qPCR and next generation sequencing. Antimicrobial resistance genes for the target antibiotics were also monitored using a qPCR approach. The results showed that none of the veterinary drugs altered the total amount of gut bacteria, but qualitative variations were observed. Tylosin treatment determined a significant decrease of α- and β-diversity indexes and a strong depletion of the rectum population (lactobacilli and bifidobacteria) while favoring the hindgut population (Gilliamella, Snodgrassella and Frischella spp.). Major changes were also observed in honeybees treated with sulphonamides, with a decrease in Bartonella and Frischella core taxa an increase of Bombilactobacillus spp. and Snodgrassella spp. Conversely, minor effects were observed in oxytetracycline treated honeybees. Monitoring of antibiotic resistance genes confirmed that honeybees represent a great reservoir of tetracycline resistance genes. Tetracycline and sulphonamides resistant genes tended to increase in the gut microbiota population upon antibiotic administration.