Abstract
The microsporidian fungus Nosema ceranae represents one of the primary bee infection threats worldwide and the antibiotic fumagillin is the only registered product for nosemosis disease control, while few alternatives are, at present, available. Natural bioactive compounds deriving from the glucosinolate–myrosinase system (GSL–MYR) in Brassicaceae plants, mainly isothiocyanates (ITCs), are known for their antimicrobial activity against numerous pathogens and for their health-protective effects in humans. This work explored the use of Brassica nigra and Eruca sativa defatted seed meal (DSM) GSL-containing diets against natural Nosema infection in Apis mellifera colonies. DSM patties from each plant species were obtained by adding DSMs to sugar candy at the concentration of 4% (w/w). The feeding was administered in May to mildly N. ceranae-infected honey bee colonies for four weeks at the dose of 250 g/week. In the treated groups, no significant effects on colony development and bee mortality were observed compared to the negative controls. The N. ceranae abundance showed a slight but significant decrease. Furthermore, the GSL metabolism in bees was investigated, and MYR hydrolytic activity was qualitatively searched in isolated bee midgut and hindgut. Interestingly, MYR activity was detected both in the bees fed DSMs and in the control group where the bees did not receive DSMs. In parallel, ITCs were found in gut tissues from the bees treated with DSMs, corroborating the presence of a MYR-like enzyme capable of hydrolyzing ingested GSLs. On the other hand, GSLs and other GSL hydrolysis products other than ITCs, such as nitriles, were found in honey produced by the treated bees, potentially increasing the health value of the final product for human consumption. The results are indicative of a specific effect on the N. ceranae infection in managed honey bee colonies depending on the GSL activation within the target organ.
Highlights
This article is an open access articleThe decline of the honey bee population and the worrying threats to their survival are currently dominating the public debate
N. ceranae, a microsporidian fungus first identified in the Asian honey bee Apis cerana, has replaced Nosema apis as a parasite of the European honey bee Apis mellifera, and it is rapidly spreading around the world [2,3]
This study aimed to explore the effect of B. nigra and E. sativa defatted seed meal (DSM) GSL-containing diets against natural N. ceranae infection on the colonies of A. mellifera in field studies
Summary
This article is an open access articleThe decline of the honey bee population and the worrying threats to their survival are currently dominating the public debate. Among the bee parasites and pathogens linked to colony decline, Nosema ceranae represents one of the primary bee infection threats [1]. The microsporidian has a tropism for the honey bee midgut epithelial cells [4], and its infection causes alteration of the homeostasis and renewal of intestinal tissues and consequent malnutrition, impaired behavior orientation, suppressed immune function and final colony losses [5,6,7]. The only registered product for N. ceranae control is the antibiotic fumagillin, a compound toxic to mammals, the effectiveness studies whereof often provided contradictory results, mostly because its use poses health risks concerning pathogen resistance insurgence and bee products contamination [8,9,10]. The role and functions of probiotics in honey bee health have recently been gaining great scientific interest [12,13,14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
