Searching for Natural Resistance to the UK’s Biggest Soft Fruit Pest with Asplins
- Growing Kent & Medway
- Jan 16
- 4 min read
Updated: 5 days ago
Asplins Producer Organisation and Niab utilised our R&D support to investigate whether specific strawberry and raspberry varieties could naturally resist spotted wing drosophila (SWD). While the project ultimately proved that varietal selection alone does not resist the pest, the research provided the industry with vital data, redirecting focus toward other essential control strategies.
At A Glance: Project Quick Facts
Project Lead: Asplins Producer Organisation (Chris Rose)
Collaborators: Niab, WB Chambers
Total Funding: £149,730 (Grant Awarded: £86,744 / Co-investment: £62,986)
Key Findings: Proven that growers cannot rely on fruit variety to resist SWD; established that the pest is opportunistic rather than selective based on sugar (Brix) or colour.
Food System Areas:
The Challenge: A Costly Invasion
Spotted wing drosophila (SWD) is the most economically damaging pest facing the UK soft fruit industry today. Unlike other fruit flies that feed on overripe produce, SWD attacks both ripe and overripe fruit, destroying crops before they can be harvested.
"It's causing enormous problems and has a big cost attached to controlling it," explains Chris Rose, Commercial Controller at Asplins Producer Organisation. "At times we're having to use control products which we're trying to avoid, [plus] lots of physical trapping and netting."
With the cost of mitigation and crop loss estimated at £20–£30 million per year, the industry urgently needed a sustainable alternative to chemical control sprays and labour-intensive physical barriers.
The Innovative Idea: Could We Breed Resistance?
The project was built on a robust biological hypothesis: could certain varieties of strawberry or raspberry be naturally resistant to SWD?
In the wild, pests often select their hosts based on specific signals. For fruit flies, these are typically the fruit’s colour and its sweetness – measured by the industry in ‘degrees Brix’. Furthermore, because the female fly must physically pierce the fruit skin to lay her eggs, researchers reasoned that varieties with tougher skins might act as a natural barrier.
The team reasoned that if they could identify varieties with lower attractiveness (specific Brix levels) or physical barriers (thicker skins) that discouraged the fly, these traits could be bred into future commercial crops.
"If we can find those [traits], then Niab in East Malling can include them in a breeding programme and hopefully find a way to control spotted wing drosophila without the high costs", Chris noted at the start of the project.
The Approach: A Large-Scale Screening Trial
Supported by a Growing Kent & Medway Large R&D grant, Asplins Producer Organisation partnered with the research experts at Niab and soft fruit growers WB Chambers to conduct extensive field and laboratory trials.
Over two years, the team screened 76 different strawberry accessions and a wide range of raspberry genotypes. They measured traits like skin firmness and Brix levels, then exposed berries to female SWD to count how many eggs were laid and how many adults emerged. This was coupled with laboratory "choice tests," offering the flies a choice between different varieties to see if they displayed a preference.
The Results: A Crucial Null Result
The value of scientific research lies in uncovering the truth, even when it challenges the initial theory.
In the first year, results appeared promising, suggesting a correlation between lower sugar levels (Brix) and reduced pest numbers. However, when the trials were repeated in the second year, these patterns disappeared. The order of susceptibility changed between varieties, and neither sugar content nor colour proved to be a reliable predictor of resistance.
Crucially, the laboratory choice tests revealed the reason why: female SWD were not influenced by fruit type. The research showed they lay their eggs on the first fruit they come across, proving that the pest is more opportunistic than selective.
While this means there is no ‘silver bullet’ variety, the finding is crucial for the industry. It provides a definitive answer: growers should not rely on planting specific varieties to resist SWD. This insight prevents years of wasted investment in breeding programmes that would not have delivered results, allowing the sector to pivot resources to other solutions.
See it Differently: Soft Fruit with Resistance to Spotted Wing Drosophila
Looking Forward: Focusing on Integrated Control
With the knowledge that varietal resistance is not a viable standalone solution, the industry can now focus its efforts on alternative non-chemical controls.
The collaboration has already positioned the partners at the forefront of other innovative research, including the development of Sterile Insect Technique (SIT) to manage pest populations. The project has also strengthened the relationship between commercial growers and research institutes, ensuring that future trials are grounded in commercial reality.
Our Support: Connecting Research to Reality
This project was funded by our Large R&D Grant scheme, which allowed businesses to derisk ambitious research projects that have the potential to change industry practices.
Chris Rose highlights the value of this regional support system: "Niab in East Malling is a Kent-based research institute. Asplins Producer Organisation is a Kent-based grower cooperative. [Therefore] the Growing Kent & Medway community seems to be a really useful route to be able to find some money that will benefit growers in Kent."
