Are there risks to wild European bumble bees from using commercial stocks of domesticated Bombus terrestris for crop pollination?

Abstract

Mass produced colonies of the Eurasian bumble bee, Bombus terrestris L., have been used in Europe for over 30 years for the pollination of horticultural crops. In recent years, the practice has been identified as a risk factor for wild bumble bees in Europe and some researchers have claimed that it is causing environmental harm. The specific risks include competitive displacement of wild bumble bees, gene introgression, and the spread of disease. We have reviewed the scientific evidence on risk factors associated with managed colonies of B. terrestris in Europe, and we highlight the strengths, weaknesses and gaps in the current knowledge base. In contrast to other reports, we conclude that there is currently not enough reliable, consistent evidence to support claims that the current use of managed B. terrestris in Europe is harmful to wild populations of B. terrestris and other bumble bees, and therefore the issue remains unresolved. In the case of disease risks in particular, there is conflicting evidence published by some researchers on the prevalence of pathogens in managed colonies versus audited data published by one of the main bumble bee producers. The current lack of consistent evidence makes it difficult for government regulators to make informed risk assessments, and we argue that more work is needed to demonstrate both the reproducibility of published findings and to understand the mechanisms of action of risk effects. Recommendations are made for future work to better understand if the proposed risks are occurring in practice and to put in place preventative measures and mitigations if required.