Real work on this has been going on since at least 2003:
BIOLOGICAL AND MICROBIAL CONTROL 2003
Field Trials Using the Fungal Pathogen, Metarhizium anisopliae
(Deuteromycetes: Hyphomycetes) to Control the Ectoparasitic Mite,
Varroa destructor (Acari: Varroidae) in Honey Bee, Apis mellifera
(Hymenoptera: Apidae) Colonies
LAMBERT HOUSSOU BLE KANGA,1 WALKER A. JONES, AND ROSALIND R. JAMES2
and
Exp Appl Acarol (2006) 40:249–258
Efficacy of strips coated with Metarhizium anisopliae
for control of Varroa destructor (Acari: Varroidae)
in honey bee colonies in Texas and Florida
Lambert H. B. Kanga
but I suspect the recent hype might have to do with the fact that this patent was granted last year:
https://www.google.com/patents/US9474776
to a mycolgist Paul Stamets whose scientific credentials and accolades include, according to Wikipedia so it must be true, having a character in 'Star Trek: Discovery' named after him.
Apparently he has asked Washington State University to "help confirm his hunches about bees and fungi"
https://news.wsu.edu/2016/11/28/researchers-feed-breed-protect-bees-survive-winter/