Most recent work by Michael Simone-Finstrom, Renata S. Borba, Michael Wilson and Marla Spivak cast doubt on the usefulness of propolis in relation to bee health:

There has been considerable interest in potential effects of propolis against bee viruses, despite little study on the subject. Current evidence suggests that the presence of a propolis envelope within the honey bee nest cavity may not influence viral loads. Borba et al. found _no difference_ in the viral loads of deformed wing virus (DWV), black queen cell virus or Israeli acute bee paralysis virus in bees from propolis-rich or propolis-poor colonies in fall or spring over two years of study.

When fractionated propolis (80% methanol extraction of propolis followed by physical and chemical fractionation) was added to artificial diet fed to G. mellonella, it _did not influence_ larval growth, and no toxic effect was observed.

We _do not recommend_ that beekeepers feed propolis solution to bees until studies adequately address the long-term effects of such a treatment. Because of the highly antibacterial and antifungal properties of propolis, it _could risk poisoning bees_ and killing the beneficial microbiome in bees’ guts that is also so critical to their health and survival

Simone-Finstrom, M., Borba, R. S., Wilson, M., & Spivak, M. (2017). Propolis counteracts some threats to honey bee health. Insects, 8(2), 46.

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html