Invasive bees and their impact on agriculture

Abstract

Increasing honey demand and global coverage of pollinator-dependent crops within the context of global pollinator declines have accelerated international trade in managed bees. Bee introductions into agricultural landscapes outside their native ranges have triggered noteworthy invasions, especially of the African honey bee in the Americas and the European bumble bee Bombus terrestris in southern South America, New Zealand, Tasmania, and Japan. Such invasions have displaced native bees via competition, pathogen transmission, and invaders' capacity to exploit anthropogenic landscapes. At high abundance, invasive bees can degrade the mutualistic nature of many of the flower-pollinator interactions they usurp, either directly by affecting flower performance or indirectly by reducing the pollination effectiveness of other flower visitors, with negative consequences for crop pollination and yield. We illustrate such effects with empirical examples, focusing particularly on interactions in the Americas between B. terrestris and raspberry and between the African honey bee and coffee. Despite high bee abundance and flower visitation in crops, theoretical and empirical evidence suggests that agricultural landscapes of pollinator-dependent crops dominated by invasive bees will be less productive than landscapes with more diverse pollinator assemblages. Safeguarding future crop yield and aiding the transition to more sustainable agricultural landscapes and practices require we address this impact of invasive bees. Actions include tighter regulation of the trade in bees to discourage further invasions, reducing invasive bee densities and dominance, and active enhancement of ecological infrastructure from field to landscape scales to promote wild bee abundance and diversity for sustained delivery of crop pollination services.