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SWD Research and Information Hub

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Gene by Gene: Understanding SWD’s Invasive Edge

Collaborative research funded by the National Science Foundation is allowing scientists at the University of Vermont, the University of Kentucky, and Northeastern University to better understand what makes the invasive Spotted Wing Drosophila (SWD; scientific name: Drosophila suzukii) so successful at infesting soft-skinned fruit crops and how we can help farmers protect their crops. Their research combines tools from ecology, physiology, and evolution. 

What are SWD?

SWD are a species of fruit fly that has emerged as a major invasive pest of small and stone fruits in the Americas and Europe since their introduction from Japan in the late 2000s [1]. Unlike other species of Drosophila that prefer overripe or spoiled fruits [8], SWD lays its eggs in soft-skinned fruits as they soften before harvest; creating visible damage that causes lost crops for local and commercial farms alike [4].

swd.png

Shane F. McEvey. (2017). Australian Museum

Basket of Strawberries
Fresh Strawberries

Adverse economic impacts

SWD invasions create problems for farmers, consumers, and the economy on a local and national scale. Despite their being no harm in ingesting SWD, infestations can cause massive yield reduction due to visible blemishes and early fruit softening and rot [4]. These economic effects having been reported in Asia, the Americas, and Europe, with a survey of growers in the eastern United States indicating an impact of $27.5 million in 2013 [6], and an estimate of $500 million in possible annual losses due to SWD-related damage in Western US production areas [7].

fruits_swd.png

Jungmin Lee. (2020). USDA ARS HCRU. 

Phil Pellitteri. (n.d.) University of Wisconsin

What are farmers doing?

Farmers and researchers alike are currently working to identify the most effective methods for SWD control. The current most prominent strategy in the US is insecticide application, which has shown to be effective and applicable for both small and large farms [2,5]. However, organic farmers have found other methods to be effective. Exclusion netting surrounding crops [9] has been found to keep SWD populations at bay, and refrigeration of harvested fruit can stop the development of larvae [3] and make fruit viable for sale. Sanitation and tillage to bury infested fruit, irradiation, and biological control are a few of the organic many practices being trialed on farms and research labs to assess efficacy for wider application [1].

nets.png

Greg Loeb. (n.d.). Cornell University-Geneva.

Apples in a Crate
Image by Alla Cheers

SWD trapping as research 

Because employment of SWD management practices in the US are based primarily on fruit ripeness levels and adult trap catches, population estimates derived from adult trapping are important to indicate pest pressure [10]. SWD capture allows for scientists to not only research the species and learn more about its behavior and biological makeup (including its genetics), it also is integral to reporting pest pressure to farmers whose livelihood relies on understanding pest behavior and population growth patterns. 

traps.jpg

Jar traps used for SWD collection. from Washington State University Extension (https://treefruit.wsu.edu/article/spotted-wing-drosophila-monitoring-for-2017/)

Our approach: using genetics to uncover the genes that underpin SWD's invasive edge

We are using tools from genomic sequencing to crack the genetic code of SWD. In particular we seek identify the genes that are changing across the growing season and how changes in those genes have impacts for our management preactices.

seasonality.png

An example of how gene frequencies change across seasons (from Bergland et al. 2014, PLOS Gen). In this plot each line is a gene, the vertical axis shows frequencies of those genes, and the horizontal axis shows different seasons across 3 years.

Basket of Strawberries
Image by Eric Chen

What can you do?

Community enhanced monitoring is one of the most effective ways that we can understand and keep track of SWD populations. If you are visiting a farm and notice berries that are very soft, collapsing on themselves, or watery near the cap of the fruit, report this to the farmers present. With the help of this place-based research, mitigation strategies can be optimized for farmers local to Vermont, and results can be distributed for future study globally.


Home gardeners can avoid pressure by planting fruits that ripen earlier in the season when the SWD populations are not as high. To minimize damage, gardeners should pick ripe fruit daily and chill immediately. Berries left unharvested or allowed to drop allow the development of larvae, increasing the adult population.

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  • For help identifying SWD, reference this guide. 

  • For help identifying SWD infested fruit, reference this guide. (Note that this Oregon-based resource is generalizable to infested East Coast fruits)

  • For questions or further information, you can call the Master Gardener Helpline at 802-656-5421 (Chittenden County residents).

References:

  1. Asplen, M. K., Anfora, G., Biondi, A., Choi, D. S., Chu, D., Daane, K. M., ... & Desneux, N. (2015). Invasion biology of spotted wing Drosophila (Drosophila suzukii): a global perspective and future priorities. Journal of Pest Science, 88, 469-494.

  2. Beers, E. H., Van Steenwyk, R. A., Shearer, P. W., Coates, W. W., & Grant, J. A. (2011). Developing Drosophila suzukii management programs for sweet cherry in the western United States. Pest management science, 67(11), 1386-1395.

  3. Bessin, J. & Bessin, R. (2022). Spotted Wing Drosophila Management. University of Kentucky Department of Entomology. 

  4. Bessin, J., Bessin, R., & Lucas, P. (2017). Spotted Wing Drosophila and Backyard Small Fruit Plantings. University of Kentucky Department of Entomology. 

  5. Bruck, D. J., Bolda, M., Tanigoshi, L., Klick, J., Kleiber, J., DeFrancesco, J., ... & Spitler, H. (2011). Laboratory and field comparisons of insecticides to reduce infestation of Drosophila suzukii in berry crops. Pest management science, 67(11), 1375-1385.

  6. Burrack, HJ (2014) SWD impacts 2013. http://swd.ces.ncsu.edu/ working-group-activities/swd-impacts-2013/. Accessed 12 July 2014 

  7. Goodhue, R. E., Bolda, M., Farnsworth, D., Williams, J. C., & Zalom, F. G. (2011). Spotted wing drosophila infestation of California strawberries and raspberries: economic analysis of potential revenue losses and control costs. Pest management science, 67(11), 1396-1402.

  8. Lee, J. C., Bruck, D. J., Curry, H., Edwards, D., Haviland, D. R., Van Steenwyk, R. A., & Yorgey, B. M. (2011). The susceptibility of small fruits and cherries to the spotted‐wing drosophila, Drosophila suzukii. Pest management science, 67(11), 1358-1367.

  9. McDermott, L., & Nickerson, L. (2014). Evaluation of insect exclusion and mass trapping as cultural controls of spotted wing Drosophila in organic blueberry production. NY Fruit Q, 22, 25-28.

  10. Tochen S, Dalton DT, Wiman NG, Hamm C, Shearer PW, Walton VM (2014) Temperature-related development and population parameters for Drosophila suzukii (Diptera: Drosophilidae) on cherry and blueberry. Environ Entomol 43:501–510

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