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Biological Control of Spotted Wing DrosophilaMegan Woltz & Jana Lee
Horticultural Crops Research Unit, Corvallis, Oregon, [email protected], [email protected]
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The invasive Spotted Wing Drosophila (SWD), Drosophila suzukii, is from Asia. It has been found in 39 or more US states. The fly lays its eggs inside intact fruit, causing economic losses in the small and stone fruit industries.
AcknowledgementsAdam Cave, Carolyn Smullin, Hanna McIntosh, Victoria Skillman, Jesse Mindolovich, Austin Cuenca NW Center for Small Fruits Grant, SCRI Grant 2010-51181-21167, CRIS 5358-22000-037-00D
Insecticide sprays provide control of SWD, but heavy use can negatively impact the environment and human health, and may risk creating insecticide-resistant fly populations. For growers that export, there is a risk of losing their crop if the fruit pesticide residues exceed the Maximum Residue Levels set by the receiving country.
Alternatives to pesticides such as biological control are currently being examined. Here we assess SWD larval predation by ambient natural enemies, and evaluate pupation habits of SWD.
• Assessed in two varieties of strawberries and potted Liberty blueberries• Green fruit bagged to prevent naturally occurring infestation• Infested at fruit ripening with 2-wk old mated female SWD for 24hr
• 3 strawberries infested with 5 flies• 15-20 blueberries infested with 8 flies
• Treatments• Unbagged – exposed to predators• Bagged – fruit enclosed in mesh to exclude predators
• 7 d post-infestation, larvae extracted via flotation in salt solution• Number of larvae from bagged and unbagged clusters compared
• general linear mixed models• infestation date as random block
• Assessed in blueberries and in primocane fruiting raspberries• Green fruit bagged to prevent naturally occurring infestation• Infested at fruit ripening with 2 wk-old mated females for 24 hr
• 15-20 blueberries infested with 8 flies• 3-5 raspberries infested with 4 flies
• Funnel placed under fruit to collect dropping fruit or larvae in soil• 14 d post-infestation, all larvae and pupae counted
• Hanging and dropped fruits dissected• Soil sieved
• # of larvae and pupae in soil vs. berries compared• Wilcoxon Signed Rank Test, non-parametric test for non-
normal data
SWD larvae develop inside fruits, but may either remain in the fruit or drop to the ground to pupate. Knowing the location of pupae is necessary to target conservation biocontrol efforts, as different groups of natural enemies forage on plant foliage and on the ground.
Naturally occurring predators consume SWD larvae inside of berries.
A significant number of pupae are found in soil, especially from dropped berries, suggesting that ground predators may be important for consuming this life stage.
Next summer we will assess predation of sentinel SWD pupae in soil.
Significantly fewer larvae were extracted from unbagged berries.Shuskan: F1,89=12.35; p=0.0007Rainier: (sqrt transformed) F1,85=3.67; p=0.059Liberty: (sqrt transformed) F1,102=4.35; p=0.0395
Do ambient predators consume SWD larvae in fruit?
Yes, fewer larvae in fruits exposed to ambient predators.
What proportion of SWD pupate in fruit and in the soil?
Most pupae were found in soil.93 % of pupae from blueberries90 % of pupae from raspberries
Photo & © Max Badgley
Minute pirate bugs, ants, spiders, and parasitoid wasps were the most common natural enemies collected in vacuum samples in these crops.
Conclusions
Soil vs. FruitPupae: S = 448.5; p <0.0001Larvae: S = -88.5; p <0.0001
Soil vs. FruitPupae: S = 110.5; p <0.0001Larvae: S = -56.5; p =0.0004
Reduction in larval survival in presence of predators:Shushkan strawberries: 34 %
Rainier strawberries: 20 %Liberty blueberries: 28 %
Photo Jack Dykinga, USDA ARS, Public Domain
Pupation habits may be affected by the fact that most of the exposed fruits dropped to the ground.
80 % of blueberries72 % of raspberries
Shuskan Rainier
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