Are there risks from pollinating crops with commercial bumblebees?

In 2015, AHDB commissioned an independent review of the scientific literature relevant to the effects of releasing non-native subspecies of bumblebees as pollinators in commercial crops. Read on to learn about what the review revealed.

The review:

In 2015, AHDB commissioned an independent review of the scientific literature relevant to the effects of releasing non-native subspecies of bumblebees as pollinators in commercial crops.

The resulting peer-reviewed paper, entitled ‘Are there risks to wild European bumble bees from using commercial stocks of domesticated Bombus terrestris for crop pollination?’, highlighted the strengths, weaknesses and gaps in the knowledge base at that time (Chandler et al., 2019). It was a comprehensive review of the available information and has become an important reference point for this subject.

Key conclusions and implications of the review:

• The authors concluded that there was insufficient reliable and consistent evidence to support claims that the use of Btt/Btd was harmful to wild populations of terrestris in the UK
• The review reported the genetic structure of Bta to be complex, with significant differences between populations from different parts of the British Isles (Moreira et al., 2015)
• The genetic structure of the sub-species that occur in mainland Europe is relatively uniform with natural genetic mixing occurring between populations (Estoup et al., 1996).
• While British and mainland European populations of terrestris do appear to partition into different genetic groups, there is strong evidence of natural genetic mixing between B. terrestris in Britain and mainland Europe.
• The authors concluded that the distinction between “native” and “non-native” terrestris was not as simple as that adopted by Natural England and the genetic make-up of these bumblebees needed to be taken into account when evaluating the environmental risks from using commercial B. terrestris.

Variation in Bta populations

There is evidence that different genetic groups (known as haplotypes) of B. terrestris vary in their susceptibility to disease, including the ability of chronic infections to build up within colonies (Manlik et al., 2017).  It is probable, too, that variations between the performance of Bta and Btt/Btd have a genetic basis.

Results of mitochondrial cytochrome oxidase I (COI) sequence analysis and microsatellite analysis had found the COI haplotype normally associated with B. terrestris populations in mainland Europe to be present in populations from various parts of the British Isles. This included areas, such as the west of Ireland, where use of commercial bumblebees is very rare.

It became apparent during the first year of the PE031b project that the trials were confounded by large variations in the numbers of adult bees in delivered hives and the subsequent development of those colonies. There was also variation in the morphology of adult bees. This variation may be explained by the genetics of the B. terrestris populations.

Variation in size of bees from a single native bumblebee hive. © Dr R J Jacobson.

Genetic studies

The decision by NE in 2015 to severely restrict the use of Btt/Btd in the UK was driven by concerns about gynes (sexually reproducing males and females, which are produced at the end of the colony’s normal lifespan) ‘escaping’ from the glasshouse and mating with native British bees to produce a genetic hybrid. However, this rested on the assumption that the B. terrestris populations that occur in Great Britain were genetically isolated from the B. terrestris bees that occupied mainland Europe. 

The project management team felt it was important that we develop in-house molecular genetics methods for B. terrestris, with the longer-term aim of providing new data on the population structure of B. terrestris that would help decision making and policy development by NE. Studies were initiated to provide DNA sequence data for the B. terrestris mitochondrial cytochrome oxidase I (COI) gene, including the identification of nucleotide polymorphisms that can differentiate between different haplotypes of B. terrestris.  

Our data has shown that there is greater sequence variation in COI than previously reported. While these are preliminary findings, they do suggest that bee ‘sub-species’ originating from Britain (labelled as Bta) and those from mainland Europe (Btt/Btd) do not consist of separate, ‘pure’ genetic entities, but rather as populations with some haplotypes in common. This would support the idea that there is already some natural genetic mixing / interactions between populations in Britain and mainland Europe - probably because the English Channel presents only a minor barrier to bee migration.

The combined genetic information has raised questions about the validity of the current classification of B. terrestris sub-species.

To find out more read the report from PE 031b: Tomato: Phase 3 of an investigation into poor pollination performance by the native bumblebee, Bombus terrestris audax.

The content on this page was authored for AHDB by Dr D Chandler,  Mrs G Prince and Dr R J Jacobson (Rob Jacobson Consultancy Ltd).