Tomato: An investigation into poor pollination performance by the native bumblebee, Bombus terretris audax

Summary: Bumblebees were first introduced to British tomato growers in 1989 via trials in glasshouse crops on the Isle of Wight. The benefits, in terms of reduced labour and improved fruit set, were so great that by 1992 bumblebees were being used to pollinate virtually all long-season tomato crops in the UK. There followed a few revisions to hive design and some tweaks to hive placement programmes, but the pollination system was so reliable that growers came to expect perfect fruit set with minimal maintenance.

 

In the 1980s, the three commercial bumblebee producers tested many populations of Bombus terrestris to determine which could be reared most efficiently in culture and which provided the best results in tomato crops. They independently selected two non-native (i.e. to the UK) sub-species; B. terrestris terrestris (Btt) and B. terrestris dalmatinus (Btd).  The British native sub-species, B. terrestris audax (Bta) was dismissed at that stage due to inferior performance. The results of that ‘internal’ company research were commercially sensitive and weren’t published. In the 27 years since the first release of non-native bumblebees in UK tomato crops, there has been no evidence of their establishment outside glasshouses or any detrimental effect on natural bumblebee populations.

 

In 2014, Natural England (NE) produced a document which suggested that non-native bumblebees could escape from glasshouses and become invasive. They suggested that non-native sub-species could possibly hybridise with wild Bta leading to the introgression of genes from non-native sub-species into the Bta genepool and local extinction of Bta. In addition, NE proposed that the use of non-native sub-species could lead to the transfer of harmful parasites / pathogens from commercially reared Bt to wild bumblebees in the UK. This document formed the basis of an open consultation on a NE proposal to change the licensing regime relating to the release of non-native bumblebees in England. The TGA had serious concerns about the quality of the evidence base available to the policy review and this was highlighted in a formal response to NE. Nonetheless, following the consultation, NE revised its policy and permission to use non-native bumblebees in unscreened glasshouses was withdrawn from 31 December 2014. Commercially reared native Bta could still be used without a license.

 

The use of Bta in 2015 proved to be far from the reliable and maintenance-free experience to which growers had become accustomed. In fact, several growers suffered such poor results that they reverted to the labour-intensive manual methods of pollination that had not been used since bumblebees were first introduced. A preliminary survey of TGA members at the end of that season indicated that 80% of respondents were ‘less than happy’ with Bta and rated their performance as only 60% of the non-native bumblebees. Some of the 20% of growers who reported adequate pollination by Bta said this had been achieved by using many more hives than had been required with Btt or Btd. However, the survey was too superficial to determine why the native bumblebees had performed so poorly.  

 

For the 2016 season, NE allowed two growers to use Btt or Btd for part of the season under a special license on condition that research was done to compare the performance of the various sub-species. Research protocols were agreed with NE which utilised bee counters to monitor activity at hive entrances. The results were inconclusive. However, the work did demonstrate that the life of the all bumblebee colonies was much shorter than growers had come to expect during the previous 25 years of reliable biological pollination. It is not known if this short life expectancy was experienced at other sites.

 

The economics of tomato production in the UK have changed considerably since bumblebees were first introduced for pollination. Pressure from retail customers has greatly reduced financial margins and growers have become dependent upon the benefits that are obtained from using biological pollination; i.e. reduced labour costs, improved fruit set, increased fruit size and better fruit shape, as well as complete truss formation in cultivars which are harvested and marketed as whole ripe trusses.

 

It is difficult to generalise about production levels and the financial value of British tomato crops due to the wide range of products supplied to our retail customers. However, if we assume the farm gate value to be about £850k / ha / season, then the total value of the British crop is about £153m / season. Long season tomato plants produce 35-40 trusses per season. The loss of set due to inadequate pollination on just two trusses equates to about 5.3% of annual production which is in the region of £45k / ha / season. The equivalent losses across the British industry would be over £8.1m. Inadequate set on additional trusses would increase losses proportionally. This would not be sustainable and could force growers out of business.

Aim: To improve the industry understanding of poor pollination performance by bumblebees in UK tomato crops

 

Objectives: 

2. Liaise with tomato growers throughout the country to answer those questions

3. Collate information into a concise reference paper