British tomato growers learn to deal with local pollinators

Prior to the introduction of bumblebees, British tomato growers used various methods of physically stimulating their plants to enhance the transfer of pollen from the males to the female parts of the flowers. For example, the Agriculture and Horticultural Development Board (AHDB) begins the story (history) below. It also discusses recent developments.

The simplest and least labor-intensive method was to water the plants or hit the crop strands with a sturdy stick, but the most effective method involved touching each flowering truss with an electrically vibrating “stick”. The latter was labor-intensive and the sticks could damage the existing fruit. All physical techniques were imperfect, as it was difficult to time the activity to coincide with the optimum state of the flowers.

As a result, the fruit set was mostly incomplete and many farmers achieved less than 80% of the crop potential. It was also common for fruits to be deformed due to uneven development of the seed, resulting in lower grades and additional financial loss.

A strange bee pollinates a tomato flower. © Dr. RJ Jacobson

The first 25 years of bumblebee pollination
The organic pollination of tomato crops with bees was introduced in Belgium by Dr. Roland de Jonge (Biobest) in the mid-1980s. Within a few years, three companies from Northern Europe were producing commercial quantities of bee colonies. They independently tested a large number of groups of Bombus terrestris in Belgium, the Netherlands and the United Kingdom to determine which can be grown most efficiently and which gave the best results in growing tomatoes. The companies independently selected two subspecies that are indigenous to continental Europe; B. terrestris (BT) and B. dalmatinus terrestris (BTD). The original British dynasty, b. Terrestris Odax (Bta), due to poor performance.

Space bumblebees were first introduced to British tomato growers in 1989 through crop-guided experiments conducted by Jerry Hyman (John Hall Nurseries) with bees introduced by Phil Walker (BCP, 1989). The benefits were so great that by 1992, bees were used to pollinate almost all long-lived tomato crops in the UK. There were some revisions to the hive design and some modifications to the hive placement programmes, but the pollination system was so reliable that growers could expect a near-perfect fruit set with minimal maintenance.

Tomatoes perfectly bear fruit by non-native bumblebees. © Dr. RJ Jacobson.

Policy change by Natural England
From 1989 to 2014, the WML-CL22 allowed tomato farmers in the UK to use non-native bumblebees to pollinate their crops. In 2014, Natural England (NE) launched an open consultation calling on stakeholders to consider their intention to revoke this permit (Natural England, 2014). The document supporting the consultation raised the possibility of bumblebees escaping from greenhouses and settling in the UK. They suggested that the alien subspecies could interbreed with wild Bta, leading to the introduction of genes from the exotic subspecies into the Bta gene pool and the local extinction of Bta. In addition, NE suggested that the use of non-native subspecies may result in transmission of harmful parasites/pathogens from commercially bred Bombus terrestris to wild bees in the UK.

The Tomato Growers Association (TGA) had serious concerns about the quality of the evidence available for the policy review. This was noted in an official response to NE. Following the consultation, Near East revised its policy and permission to use non-native bumblebees in unexamined greenhouses was withdrawn as of December 31, 2014. Commercially grown native Bta can still be used without a permit.

Early experiences with Bta
The use of Bta during the first season (2015) was found to be less reliable and more maintenance intensive compared to the exotic subspecies that farmers are accustomed to. In fact, many farmers have had such poor results that they have reverted to labor-intensive manual pollination methods that have not been used since the introduction of bumblebees.

An initial survey of TGA members, conducted via email at the end of the 2015 season, found that 80% of participants were “less than satisfied” with Bta, rating its performance as only 60% of non-native bumblebees. Some of the 20% of farmers who reported adequate inoculation with Bta said this was achieved using more colonies than was required with Btt or Btd.

What has happened since 2015?
Tomato growers in the UK continue to have intermittent problems with poor fruit set and incur significant financial losses in some cases, especially during warm weather.

In 2016, the TGA Technical Committee collaborated to conduct an in-depth survey of UK tomato growers to gather more information about the situation and prepare a knowledge base to build an actionable research programme. With the PE031 Subsequent Project Series, UK tomato growers are now trying to better understand tomato pollination from Bta so that this subspecies can be used without significant economic loss.

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AHDB