Can commercially imported bumble bees out-compete their native conspecifics?
Although invasive species are major topics of research, little consideration has been given to the implications of introducing non-native subspecies or beneficial organisms such as pollinators. However, the extensive trade in bumble bees as pollinators of glasshouse crops involves both. Within regions in Europe, the importation of non-native commercially reared subspecies of Bombus terrestris could endanger native bumble bees through competitive displacement and/or hybridization. This study made a direct ecological comparison between commercially imported and native B. terrestris colonies growing in the wild in the UK. In particular, using a paired design, we compared the nectar-foraging performance and reproductive outputs of commercial and native colonies growing under identical field conditions. Commercial colonies performed well in the field, with substantially higher nectar-foraging rates than native colonies in four out of five locations. Nectar-foraging performance was positively correlated with forager size, with commercial bees being consistently larger than native bees. All seven commercial colonies studied produced gynes (new queens), with two colonies each producing in excess of 50. In contrast, only two out of seven native colonies produced gynes, and those only produced small numbers (five in total). Males were produced by all colonies but there were no significant differences in numbers between commercial and native subspecies. Synthesis and applications. The high reproductive success of commercial colonies indicates that there is an appreciable risk that they will become established and spread within the UK. Furthermore, their superior foraging ability and large colony size could lead them to out-compete native bumble bees. Clearly the invasive potential of non-native subspecies and/or beneficial organisms should not be overlooked. With respect to the current importation of commercial bumble bees, we strongly recommend a precautionary approach: native species and subspecies should be locally reared and the use/disposal of bees should be strictly regulated.