How to Take on Spotted Wing Drosophila With IPM
October 16, 2019 
Researchers are looking at natural enemies to combat spotted wing drosophila. Among the most promising IPM options is a beneficial wasp from the genus Ganaspis.
Photo by Tim Haye
When spotted wing drosophila (SWD) arrived in the U.S. and Europe, a lot of small fruit growers and tomato growers were forced to abandon their integrated pest management (IPM) programs in order to continue to harvest their crops. However, growing research around the globe is revisiting the concept of integrated pest management within the guise of spotted wing drosophila control.
Dr. Lukas Seehausen, a Research Scientist in Risk Analysis and Invasion Ecology with Centre for Agriculture and Biosciences International (CABI) in Delémont, Switzerland, is a part of a team of researchers across the globe looking at current SWD IPM practices and their effectiveness. While their initial findings were published in the Journal of Pest Science in 2016, the research continues as the threat of SWD grows. Seehausen says when it comes to what the team has learned so far in their work with SWD, IPM is essentially the best and only approach.
“There is no ‘silver bullet’ against SWD and for most invasive pests,” he says. “There is no single solution for its control. Integrative combinations of control measures are needed to bring damage to an economically acceptable level.”
Initial Findings
It’s critical to understand SWD’s habits to make informed crop and variety choices. Researchers around the globe have identified red or darker-colored fruit with thin skin as SWD favorites for oviposition, so selecting varieties that might be less desirable to the pest can give you a leg up on control. Also, Seehausen says growers can implement things like exclusion netting and lure traps, as well as sanitary measures to remove fallen or overripe fruits to control SWD populations.
“Mass trapping of flies in open crops has so far not been shown to be an effective measure,” he says.
Lukas Seehausen
Instead, as others’ research indicates, a more effective control measure would be to harvest in intervals to keep the pest out of the perfect fruits.
“SWD adults preferentially lay eggs in ripe or slightly overripe fruits,” he says. “Short harvesting intervals can therefore reduce the number of infested fruits.”
Seehausen says that traditional chemical controls are effective for short-term local pest control, but some traditional chemical sprays and biopesticides should be limited to prevent pest resistance. Research has shown some promising alternatives to broad-spectrum pyrethroids and organophosphates.
“The application of calcium hydroxide or kaolin on ripening fruits has been shown to successfully prevent oviposition by SWD adults,” he says. “These products do not kill beneficial insects and are harmless to humans and, therefore, can be incorporated into an IPM program for certain crops.”
Classical Biological Control
Seehausen’s research team has examined the prospects of natural enemies for a biological control program. After studying several species of parasitoid wasps from Asia, the most promising has been from the genus Ganaspis. The challenge has been that the suitability for biological control can vary because there are at least two different, but very similar, species of this wasp. The hope, though, is as researchers zero in on the feeding habits of this species of wasp, natural enemies can help contain and control populations within and outside the farm, in natural environments.
“Even if effective, such a natural enemy will not eradicate SWD. The combination of several pest management approaches within an IPM program will likely be necessary to lower damage to an economically acceptable level,” he says. “Given natural dynamics between parasitoids and their hosts, the control imposed by the parasitoids is most likely to not work everywhere and at all times. In some locations, and when parasitoid populations are low, additional measures will have to be taken in order to prevent and reduce damage caused by the SWD.”
While it’s not a new finding, Seehausen says growers need to understand the difference between area-wide pest control and targeted control, and the difference between short- and long-term control. It’s easy for growers to consider controlling the pest on their farm, but to truly control SWD, you must think more broadly.
“Growers have to think long-term and beyond the borders of their own property,” he says. “SWD attacks wild fruits, too, and re-infests crops effectively from the natural environment,” he says. “Measures taken against the fly in a crop only provide local and short-term control.”
This is where Seehausen says using combinations of IPM methods is more effective throughout the season, with the hopes of reducing the overall pest pressure and population.
Benefits to IPM
While growers are familiar with the reasons behind implementing an IPM program, Seehausen says the best way to understand the concept of IPM is to liken it to a toolbox – whether that be parasitoid wasps, exclusion netting, trapping thresholds, environmental controls, etc.
“A carefully planned IPM program allows growers to use several tools from this box, which together will be more useful and effective in handling the problem. IPM is also about not carrying all eggs in one basket, so that if one pest management option turns out to not work very well, other control measures are in place.”
But your IPM program is only as good as you know how to use it.
“IPM techniques are only effective if applied at the right moment. For example, nets can only be used after flowering but before the fruits begin to ripen. If mounted too early, pollination will not take place and if mounted too late, SWD will already be on or in the fruits,” he says.
Knowing when and where SWD is present on your farm is critical, which means using lure traps and monitoring. It’s also a good idea to stay informed as to what kind of new control options are available in case you need them, because, as Seehausen likes to say, there’s no one-shot solution for SWD.
“SWD is here to stay, and we have to learn how to deal with it in the long term,” he says.
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