For much of the past 10 years, beekeepers, primarily in the United States and Europe, have been reporting annual hive losses of 30 percent or higher, substantially more than is considered normal or sustainable. A 2015 report from a United Nations group found that populations are declining for 37% of bee species. Most recent studies have focussed on the role of pesticides in the bee decline. A recent study of bumble bees in the U.S. has identified fungicides as a possible cause of bee decline. Fungicides have been largely overlooked in studies of declining bee populations.
Several species of bumblebees have recently experienced range contractions and possible extinctions. A new study used machine learning statistical methods to analyze the role of 24 different factors in explaining the decline of four bumblebee species, tracked at 284 sites across 40 US states. These included latitude, elevation, habitat type and damage, human population and pesticide use. The analysis assessed which variables predicted pathogen prevalence and range contractions via machine learning model selection techniques. It was found that greater usage fungicides was the best predictor of pathogen prevalence in four declining species of bumblebees. It is hypothesized that fungicides kill beneficial gut microbes in bees.
Landscape predictors of pathogen prevalence and range contractions in US bumblebees, Scott H. McArt, Christine Urbanowicz, Shaun McCoshum, Rebecca E. Irwin, Lynn S. Adler, Proceedings of the Royal Society B, 15 November 2017. DOI: 10.1098/rspb.2017.2181