Developing a push-pull approach to SWD control

Title: Innovative push-pull control of spotted wing drosophila, an invasive pest of fruit crops
Funder: Innovate UK
Industry partners: Russell IPM, Rumwood Green Farm, University of Greenwich (NRI), WB Chambers
Term: April 2023 to March 2025
 

Previous research carried out by PhD student Christina Conroy as part of the CTP for Fruit Crop Research studentship scheme, identified a chemical repellent that causes a reduction in egg laying in strawberries up to six metres away from the sachet containing the repellent. Other research has demonstrated how precision monitoring traps can be used to reduce overwintering populations in habitats such as woodland adjacent to fruit crops in the winter.

The project

Working with industry partners, Niab set out to combine these findings into a push-pull approach to improve management and control of the pest. They set out to test the repellent compound in raspberry crops then carried out further trials in a commercial strawberry crop, combining the repellent inside the crop (to push the pest out of the crop), with a lure around the perimeter of the crop (to pull the pest away from the crop). Further work was done to optimise existing repellents and attractants for use by commercial growers.

Results

Disappointingly, in testing the repellent compound in 12m long mini-tunnels planted with raspberry, no clear reduction in SWD egg laying was recorded, despite increasing the dose of the compound.

In the push-pull experiment in a commercial strawberry crop over two years, no reduction in egg laying was recorded. Further testing was done using double the number of repellent dispensers, sampling fruit close to dispensers, deploying dispensers in the crop from planting onwards, and including Russell IPM’s commercially available MagiPal.

The MagiPal product, demonstrated to attract natural enemies into crops, was also shown by Christina Conroy in the laboratory to be repellent to SWD. However, despite making these adjustments, no further egg reductions were observed. These results were disappointing and demonstrate how difficult it is to control SWD in a commercial setting even though laboratory and small field tests can initially look promising. It is likely that other factors in commercial crops prevent the repellent working. For example the size of the fields and how the fly perceives the cropping area through vision, detection of fruit and yeast volatiles, and climatic conditions.

In seeking to optimise attractants (the pull component), the Niab team had an idea of a component that might be blended into the liquid products developed by Russell IPM to improve attraction. Liquid baits were compared to standard commercially available liquid baits in field trials. Encouragingly, the newly developed Russell IPM blend was as attractive as the standard Gasser bait which is no longer available. This was an encouraging result, showing that a UK produced bait can be substituted for a bait produced overseas, thereby reducing transport costs and carbon footprint.

Niab is extremely grateful to the commercial growers who hosted this research, without whom the work would not have been possible.

Previous work by Niab has shown that practising winter precision monitoring year after year can help to reduce local numbers of SWD on farms over time and particularly in crops in the spring. Traps should be positioned in hedgerows and woodland, especially in areas of bramble, elder and ivy.