Latest research findings in AHDB research project SF/TF 145a

Since 2013, the AHDB has been funding research into the management and control of spotted wing drosophila (SWD) and in that time we have greatly enhanced our knowledge and understanding of how SWD behaves in UK growing conditions and the best management and control options available to growers. In addition to monitoring populations and activity of the pest at NIAB EMR in Kent, we continue to fund investigations into novel approaches to control the pest whilst reducing reliance on conventional spray control products. The work is being led by NIAB EMR in association with the James Hutton Institute in Project SF/TF 145a. 

Developing a push/pull system 

The aim of this work is to combine the use of repellents and attractants, so that the pest can be pushed away from the crop using a repellent and attracted into a trap containing a fatal component. 

• Yeasts are known to attract SWD adults, so in Project CP 171, PhD student Rory Jones at the University of Lincoln has been collecting volatile compounds from yeast species associated with SWD and identifying them with the hope of developing new attractants
• Research by CTP Student Christina Conroy (Project CTP FCR 2017 1) has identified at least three potential repellents which reduced numbers of SWD and subsequent egg laying in raspberry fruit in laboratory and field tests. One of these reduced egg laying in a field study polytunnel containing strawberry
• NIAB EMR entomologists developed a prototype ‘attract and kill’ trap which has compared favourably to a commercially available alternative. Both achieve up to 30% kill of SWD adults within 24 hours in semi-field cage trials. However, crucially in the presence of ripe fruit, the efficacy of both devices decreased by half, suggesting that these traps/devices should be deployed in early spring, outside the crop, when there is no competition from ripening fruit and SWD populations are at their lowest
• Other work has focussed on developing a dry formulation of the ‘Cha-Landolt’ lure, which is contained within a sachet. This saves time on weekly changes of the liquid lures whilst also lasting up to six weeks 

Bait sprays

Using bait sprays in combination with spray control products should help to attract SWD adults to feed on the spray product, improving the likelihood of control. When compared to a spray control product on its own, it offers the potential to gain the same level of control with a lower rate of product. In field trials we assessed two baits, a yeast (Hanseniaspora uvarum) and the commercially available Combi-protec, both combined with Benevia (cyantraniliprole), with a standard foliar application of Benevia. The baits were applied as a band across the top of the strawberry plant canopy with a specialised nozzle providing course droplets. 

• The baits gave comparable control to the foliar spray.  The Combi-protec band spraying (half the rate of the foliar spray) was as good as foliar full rate application. Additionally, foliar applications of Benevia (full rate) were effective for two weeks after the last application 

Prolonging spray intervals in cherry

This work investigated whether we might prolong spray intervals beyond 7-10 days. The scientists compared the use of weekly versus fortnightly spray programmes to control SWD in protected cherry 

• Fortnightly sprays gave comparable efficacy to weekly sprays in cherry crops. The work was repeated for a second season and the results were similar
• It was also noted that where mesh was employed to exclude SWD from the crop, there were fewer adult SWD in the crop 

Reducing winter populations of SWD through precision monitoring

We have investigated a new concept of reducing overwintering populations through precision monitoring. Earlier research has demonstrated that populations of SWD peak in the autumn and early winter, but as available fruits in crops decline in number, adults disperse into hedgerows and woodland for food and protection over the winter period. 

NIAB EMR entomologists used a grid of precision monitoring traps within woodlands at six sites through the autumn and winter months to attempt to ‘mop-up’ numbers and thereby reduce the populations of adults emerging from the woodland in spring. They compared SWD populations with those in untreated woodlands on the same sites. They also tested egg-laying incidence using sentinel fruit placed adjacent to all 12 woodlands in the spring. 

• Numbers of SWD in the precision monitoring woodland decreased, while populations in the untreated woodland continued to rise
• Numbers of SWD caught in traps positioned on the perimeter of the woodland were higher than those in other locations
• Further work will assess if long-term placement of these traps can suppress local SWD populations over time 

Potential organic forms of control

In associated work which has been part-funded by Berry Gardens and The Worshipful Company of Fruiterers, entomologists at NIAB EMR searched for insects that parasitise SWD. They have been trapping SWD from wild areas and identifying parasitoids emerging from SWD pupae. 

• Five species have been identified and the scientists are currently trying to estimate the percentage parasitism by UK parasitoids in the wild