Sterile insect technique to become available for SWD control

At the NIAB Soft Fruit Day technical webinar on 30^th November, Glen Slade, founder and CEO of BigSis, presented the results of trials conducted in 2022 leading to the launch of the company’s sterile insect technique (SIT) service for farm-scale SWD control.

SIT, Mr Slade explained, involves the production of sterile males to be released into the field to mate with wild females resulting in no offspring, thus achieving effective population control.

Although the technique was developed over 60 years ago, it has typically been used in area-wide projects by government bodies and has not been released for commercial use to date. BigSis aspired to change the status quo and reinvented the rearing process of sterile SWD using robotics and AI to be able to offer the service for farm-scale, season-long control.

To illustrate the value of SIT to growers, Mr Slade outlined the costs associated with SWD control throughout the season, estimated to be around £11,000 per ha by AHDB. The costs are split between product and labour expenses and include:

• Chemical insecticides
• Re-application of biocontrol
• Maintenance of better hygiene
• Frequent picking
• Netting deployment

With SWD control costs reaching into the tens of thousands on larger farms, Mr Slade highlighted the sizeable cost-saving opportunity offered by SIT, which not only beats chemicals in efficacy and duration, but is also fully sustainable.

2021 world-first field trial in Kent

The first field trial of the BigSis SIT was performed on strawberry crops in partnership with NIAB and Berry Gardens. The trial ran for three months from July to September and compared SWD numbers on two untreated plots with a third plot treated with SIT.

The results have shown suppression of up to 91% of SWD on the treated site, with low numbers persisting throughout the season. In contrast, untreated plots had high rates of infestation that remained elevated even after the use of insecticides.

Since BigSis SIT is a non-toxic, non-GMO solution, no permit was required for its sale in the UK, leading to its unprecedented speed to market. The technique uses native strains to target specific species, without having any impact on beneficial insects, Mr Slade explained.

What’s more, since sterile insects can’t establish in the environment, they aren’t a long-term addition to the existing SWD population on the field.

Moving towards automation

So far, the production of sterile SWD males has relied on manual rearing, which is unreliable and difficult to scale up, Mr Slade said. Failure to achieve consistency of released numbers has caused the company to miss its 2022 targets of servicing 16.6 ha in addition to conducting field cage trials.

To combat this issue, BigSis has been developing an automated system for producing sterile male SWD. As of this year, the company’s pilot micro-production unit (MPU) has reached an operational stage, meaning the rearing process of sterile insects is now fully automated.

Mr Slade and his team are currently working on scaling up the pilot MPU to a full market production unit, which will then be used to service expanded projects in 2023.

While the company hasn’t been able to repeat season-long control in trials planned for this year, suppression of SWD was demonstrated at every site where SIT was employed, proving the effectiveness of the technique.

Suppression in raspberry field cage study

Mr Slade also shared the results of a field cage trial where sterile SWD was released in raspberry crops alongside wild male and female insects. The trial measured the number of larvae per fruit instead of measuring trap counts as usual.

In crops used as control, both wild males and females were released with no sterile SWD, which caused a build-up in population and infestation of fruit.

Whereas, treated crops had 5, 25, and 100 sterile SWD released for every wild male and female. All three treatments kept the infestation under control and larvae numbers low.

However, when dealing with nature, there is always an element of unpredictability. Mr Slade believes this might have affected the performance of the 25:1:1 treatment, which didn’t bring SWD numbers down as expected. Therefore, the decision was made to up the ratio to 100:1:1, which made sure infestation levels came under control.

Summarising the results of the trials, Mr Slade reiterated that significant control was achieved whenever sterile insects were released on fields, leading to season-long suppression of SWD populations.

It was also ascertained that smaller plots are more vulnerable to ‘border effects’ due to the higher likelihood of SWD migrating across from neighbouring fields. As a result, a minimum size of 7 ha will be retained for future projects, Mr Slade said.

In addition, since trial results have varied between strawberry and raspberry crops, the team concluded that optimal release rates and tactics must differ between crops. Further analysis of how different crop dynamics affect SWD control by SIT will therefore be needed for better decision-making.

Next steps

With the large-scale automated production unit currently in development, BigSis is hoping to roll out millions of sterile SWD per week and service hundreds of hectares in 2023.

Moreover, the company plans to offer season-long control of SWD as a service, Mr Slade revealed. This will involve trained staff handling the release of sterile insects and setting up monitoring traps on farms for a more targeted strategy.

The idea behind the service, Mr Slade explained, is to provide growers with a zero-hassle solution to SWD control with no labour or learning required from the farm.

In addition, BigSis will be adopting a multi-channel distribution in the future, relying on trusted partners to integrate inputs, Mr Slade said. So far, the service has only been available to Berry Gardens growers to reflect the help given to get the product to this stage.

However, an announcement of additional hectares to add to the service will be made in 2023. To keep up to date with the BigSis SIT project, visit: https://bigsis.tech/