Bombus terrestris, pollinator, invasive and pest: An assessment of problems associated with its widespread introductions for commercial purposes

Bombus terrestris L. (Apidae) is a native of temperate Eurasia and has been moved around the world since the 1800s. Dispersal of B. terrestris gained momentum in the 1980s when bees were reared artificially in Europe and supplied commercially for greenhouse pollination services. Very early after its commercial introduction, it was recognized that this species is invasive, can island hop to new locations and may disturb local ecosystems. The invasive characteristics of B. terrestris are: high migration ability, early seasonal emergence, high adaptability under adverse climatic conditions in various habitats, generalist or polylectic foraging strategies, enabling it to work a wide variety of flowers for resources, foraging over wide distances, a thermoregulatory metabolism that enables it to withstand low temperatures, no natural enemies to check population growth in areas outside its natural range, and it may develop two reproductive cycles in a year (bivoltine) in a newly colonized area. In addition, commercial bees produce more gynes and are better competitors than the local conspecific populations and may replace them in the likely event of an escape. The documented evidence on invasive impact of B. terrestris on natural ecosystems includes: negative interactions with local bee fauna, competition for nest sites with, and genetic contamination of, local Bombus spp., spread of parasites and pathogens and negative interactions with plant reproductive capacity. We discuss the possible measures that must be taken to minimize the B. terrestris invasion on local as well as on global levels.