Bronwen Roy: Molecular screening reveals a wider geographic and host range for a novel stingless bee disease.

Our limited knowledge of stingless bee diseases is disconcerting in light of their growing importance in commercial pollination. The first description of a brood disease in stingless bees was only reported in 2017. This implicated Lysinibacillus sphaericus a common soil bacterium as the casual pathogen in Western Sydney in T. carbonaria and A. australis hives. However, the geographic and host ranges of the disease have yet to be investigated. In this study 50 healthy hives and 10 “sick” hives were tested for the bacterium using a species-specific qPCR. Key findings were that 1) L. sphaericus was only detected in “sick” hives (i.e. those exhibiting a sudden dumping of discoloured larvae, and with reduced foraging activity) and 2) sick hives were not restricted to Western Sydney, but also found in other sites in NSW and in Queensland. Additionally, the host range included an additional bee species, T. hockingsi. Analyses of L. sphaericus DNA sequences from infected larvae from all 10 sick hives suggest that the pathogen is a specific non-toxigenic strain of L. sphaericus. While the mechanism of transmission remains elusive, it appears that the bacterium does not form part of the normal commensal flora of stingless bees, and that the spread of the disease is probably introduced from external environmental sources.