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Spotted wing drosophila key focus of trial work

Certis has commissioned new trial work focusing on the effect of its product, Spruzit (pyrethrin + rapeseed oil) on the newly arrived pest, the spotted wing drosophila (SWD).

Adult male SWD
SWD breathing tubes

Certis has commissioned new trial work focusing on the effect of its product, Spruzit (pyrethrin + rapeseed oil) on the newly arrived pest, the spotted wing drosophila (SWD). The laboratory-based study was carried out by Dr Michelle Fountain and Bethan Shaw at East Malling Research (EMR) and produced some encouraging results.

SWD has the potential to be a damaging pest in UK soft and stone fruit. The first sighting of this pest in the UK, in autumn 2012, was anticipated, yet was still a cause for concern. SWD has the ability to rapidly spread in the environment and, with a lifecycle of around a month, to multiply very quickly especially in protected crops.

Unlike the native drosophila species, only laying eggs in overripe fruit, SWD can lay eggs in fruit as it starts to ripen as well as when overripe. This makes SWD a more challenging pest for growers to manage.

Dr Fountain emphasises that instances of SWD in the UK have been low, to date, but nonetheless, says it is important to monitor this pest and be aware of the potential damage it can cause. “These types of pests are not unfamiliar to growers, but it remains important to be prepared and understand the challenges posed by this particular pest.”

The laboratory trial focused on blueberry fruits and the effect that Spruzit (applied at half the label rate) has on larval development and adult SWD. The trial encompassed two experiments with this established IPM compatible treatment. In the first experiment the fruit was dipped, as per standard laboratory protocol, in Spruzit prior to being exposed to the SWD pest.

The second trial, focused solely at testing the effect of Spruzit on adult SWD. Though this research has been positive and showed encouraging results for Spruzit, there is further scope for in-field research.  

There was variability in the data, but on average Spruzit showed efficacy at controlling SWD. There was a 60% reduction in visible breathing tubes (an indicator of egg laying) on the surface of the fruits compared to the control, and 40% fewer emerging adults. Other current research, conducted at EMR, with strawberries showed that pyrethrins protected the fruit against SWD egg laying for a 2-3 day period; the experiment with Spruzit on blueberries demonstrated similar results.

Spruzit’s activity targets both the flying adults and their subsequent ability to lay eggs or for early life stages to survive.  

Alan Horgan, Certis’ Technical Officer comments, “The temperature and humidity conditions in the UK could be very conducive for SWD, especially in polytunnel soft fruit production. With that in mind, it was important to look for the weakness in the SWD lifecycle and identify how Spruzit could be employed to reduce the incidence and spread.”

Alan explains why Spruzit is likely to be effective on SWD. “Once the pest’s eggs are laid in the fruit, breathing tubes are sent up to the fruit surface. It is possible that Spruzit, with its natural oil content, is affecting the ability of the breathing tubes to function, and the pyrethrins may also be affecting the eggs in some way. Spruzit can already be applied to all soft fruits where it has excellent activity on the range of target pests. So, I hypothesised it would have an effect on SWD.”

Dr Fountain urges growers to deal with SWD through a planned and programmed approach including monitoring for the arrival of the pest in the crop using traps, “Control measures should initially concentrate on crop hygiene; removing waste fruits from the crop and then disposing of the fruit so that is doesn’t become a source of SWD contamination. There are very few SWD effective insecticides available to the soft fruit industry, so it is important that growers rotate the modes of action available and that they apply integrated pest management (IPM) to control this pest to prevent the occurrence of insecticide resistance and resurgence of other pest species”.

“The US has conducted a lot of research into SWD, and Italy has been dealing with this pest for three years now,” notes Michelle. “Both countries have provided valuable insight and understanding on how UK growers can protect their crops, and manage this new pest.”

Dr Fountain explains that crop hygiene and trapping can help in the fight against SWD. “Crop hygiene, removing all non-saleable, and dead or damaged fruit from plants and storing all waste fruit in a sealed, release valve container, is crucial to help prevent attracting the pest.

“It is important to keep populations of SWD low, particularly from July onwards. Trapping to monitor for the pests arrival and population increase is crucial,” notes Dr Fountain. East Malling Research and the Natural Resources Institute at the University of Greenwich are producing a robust synthetic attractant and trap for this purpose.

Alan comments, “Spruzit has a short persistence, its efficacy lasts for a two day period, after which biologicals can be used as part of a wider IPM control programme for existing pest challenges.”

Spruzit has the potential to be incorporated as part of an IPM programme in the control of SWD as an effective part of the tools available to growers. There has been significant progress made in understanding and managing SWD, however there is still a lot more to find out about this pest and how to target control measures.