Chito-Oligosaccharide and Propolis Extract of Stingless Bees Reduce the Infection Load of Nosema ceranae in Apis dorsata (Hymenoptera: Apidae)

Abstract

Nosema ceranae is a microsporidian that infects Apis species. Recently, natural compounds have been proposed to control nosemosis and reduce its transmission among honey bees. We investigated how ethanolic extract of Tetrigona apicalis’s propolis and chito-oligosaccharide (COS) impact the health of N. ceranae-infected Apis dorsata workers. Nosema ceranae spores were extracted from the guts of A. florea workers and fed 106 spores dissolved in 2 µL 50% (w/v) sucrose solution to A. dorsata individually. These bees were then fed a treatment consisting either of 0% or 50% propolis extracts or 0 ppm to 0.5 ppm COS. We found that propolis and COS significantly increased the number of surviving bees and lowered the infection ratio and spore loads of N. ceranae-infected bees 14 days post-infection. Our results suggest that propolis extract and COS could be possible alternative treatments to reduce N. ceranae infection in A. dorsata. Moreover, N. ceranae isolated from A. florea can damage the ventricular cells of A. dorsata, thereby lowering its survival. Our findings highlight the importance of considering N. ceranae infections and using alternative treatments at the community level where other honey bee species can act as a reservoir and readily transmit the pathogen among the honey bee species.