EM 9263    Published December 2019

SWD series #3

Key points in this fact sheet

  • Commercially important fruits in Oregon susceptible to spotted-wing drosophila (SWD) (from most susceptible to least susceptible) include raspberry, strawberry, blackberry, cherry, blueberry and table grapes (Figure 1).
  • Other fruits such as peaches, cranberries and wine grapes are susceptible when damaged. Other commercial fruit that are intact are not likely to be infested in the field.
  • Key fruit characteristics indicating susceptibility to SWD are firmness and °Brix (sugar). Increasing sugar and decreasing firmness are correlated with increased susceptibility to SWD damage.
  • The easiest way to determine fruit susceptibility is to measure sugar content.
  • Probability of SWD infestation increases above 50% when Brix level increases above 10°Brix.
  • Fruit are usually too firm for SWD egg-laying when the sugar levels are below 10°Brix.
  • Most wine grape cultivars resist SWD because of the firmness of the skin.
  • Pest pressure on an individual crop can vary from season to season.

Fruit that are susceptible to SWD

Spotted-wing drosophila can develop on a wide range of cultivated and wild, soft-skinned fruits. This complicates pest management because SWD populations can move among several hosts with different ripening times throughout the year, allowing them to survive and reproduce in many environments.

Host susceptibility is influenced by such characteristics as color intensity, sugar content (°Brix), flesh firmness, penetration resistance of the skin, and acidity. Fruits become more susceptible to SWD as they begin to take on color and ripening progresses. Maturation indices predict the risk of infestation. For example, blueberry fruit are often not sprayed until the onset of coloration. As fruit ripens, sugar content increases, whereas penetration resistance, firmness and acidity decrease (Figure 2).

The increase in sugar content is the easiest way to determine fruit susceptibility and can be measured directly in the field with a refractometer. Fruit are usually too firm for SWD egg-laying when sugar levels are below 10°Brix. Above that threshold, the probability of SWD infestation increases by 50%.

Differences in susceptibility between cultivars are influenced by physical characteristics such as texture, firmness, and the force required to penetrate the skin. Selecting thicker-skinned cultivars of cherry, blueberry, peach and grape may reduce SWD infestation. SWD are less successful and spend more time trying to lay eggs in thicker-skinned fruit. In cherries, cultivars that are resistant to fruit cracking also limit SWD infestation and their population buildup.

Multiple studies indicate that SWD do not prefer wine grape as a host. The majority of grape cultivars resist SWD attack during the harvest period because of relatively high skin penetration resistance. Nonetheless, SWD are able to lay eggs in damaged fruit and intact fruit of soft-skinned varieties. SWD feed on damaged berries during the harvest period. When berries are cracked, diseased or damaged by birds, heavy rainfalls or hail, levels of SWD feeding and egg laying increase, along with the possibility of spreading spoilage bacteria and fungi.

Further reading

Bellamy, D.E., M.S. Sisterson, S.S. Walse. 2013. Quantifying host potentials: indexing postharvest fresh fruits for spotted wing drosophila, Drosophila suzukii. PLoS ONE 8: e61227.

Burrack, H.J., G.E. Fernandez, T. Spivey, D.A. Kraus. 2013. Variation in selection and utilization of host crops in the field and laboratory by Drosophila suzukii Matsumura (Diptera: Drosophilidae), an invasive frugivore. Pest Management Science 69 (10):1173–80

Diepenbrock, L.M., K.A. Swoboda-Bhattarai, H.J. Burrack. 2016. Ovipositional preference, fidelity, and fitness of Drosophila suzukii in a co-occurring crop and non-crop host system. Journal of Pest Science 89(3): 761–769

Entling, W., S. Anslinger, B. Jarausch, G. Michl, C. Hoffman. 2019. Berry skin resistance explains oviposition preferences of Drosophila suzukii at the level of grape cultivars and single berries. Journal of Pest Science 92(2): 477–484.

Ioriatti, C., V. Walton, D. Dalton, G. Anfora, A. Grassi, S. Maistri, V. Mazzoni. 2015. Drosophila suzukii (Diptera: Drosophilidae) and its potential impact to wine grapes during harvest in two cool climate wine grape production regions. Journal of Economic Entomology 108(3): 1148–1155.

Ioriatti, C., R. Guzzon, G. Anfora, F. Ghidoni, V. Mazzoni, T.R. Villegas, D.T. Dalton, V.M. Walton. 2018. Drosophila suzukii (Diptera: Drosophilidae) contributes to the development of sour rot in grape. Journal of Economic Entomology 111(1): 283–292.

Little, C.M., T.W. Chapman, D.L. Moreau, N.K. Hillier. 2016. Susceptibility of selected boreal fruits and berries to the invasive pest Drosophila suzukii (Diptera: Drosophilidae). Pest Management Science 73(1):160–166

Lee, J.C., D.T. Dalton, K.A. Swoboda-Bhattarai, D.J. Bruck, H.J. Burrack, B.C. Strik, J.M. Woltz, V.M. Walton. 2016. Characterization and manipulation of fruit susceptibility to Drosophila suzukii. Journal of Pest Science 89, 771–780.

Lee, J.C., D.J. Bruck, H. Curry, D. Edwards, D.R. Haviland, R.A. Van Steenwyk, B.M. Yorgey. 2011. The susceptibility of small fruits and cherries to the spotted-wing drosophila, Drosophila suzukii. Pest Management Science 67, 1358–1367.

Stewart, T.J., X. Wang, A. Molinar, K.M. Daane. 2014. Factors limiting peach as a potential host for Drosophila suzukii (Diptera: Drosophilidae). Journal of Economic Entomology 107(5): 1771–1779.

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