A preprint of a very interesting paper was published this month on the subject of bee decline: Eduardo E. Zattara and Marcelo A. Aizen, Global Bee Decline. Dec. 10, 2019; doi: http://dx.doi.org/10.1101/869784. They found the numbers of collected bee species recorded in global occurrence records sourced from the Global Biodiversity Information Facility have decline today to half of those recorded in the 1950s.
Plants and Pollinators 