Optimizing the Salt Filter Test to Monitor Spotted Wing Drosophila Larval Infestation Levels in Blueberries
Davis, Amelia R.
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Spotted wing drosophila (SWD), or Drosophila suzukii, is an invasive pest that has cost the United States millions of dollars in crop losses since its first detection in the country in 2008. SWD develops through three larval instar stages between egg and adult and its short generational turnover and unique morphology makes it a serious threat to soft-skinned fruit agriculture. The salt filter test monitoring method described in this study offers accurate quantification of larvae in all instar stages. However, until the present study, variables such as incubation time, fruit crushing, and solution type had not yet been optimized for the salt filter test method. This study found that salt filter testing was significantly more accurate than unfiltered assessment methods for quantifying SWD larvae of all instar stages in blueberries. Additionally, for detecting first instar larvae, allowing at least 30 minutes for incubation is recommended, but for second and third instar larvae, incubation times higher than 15 minutes did not significantly increase larval yield. Similarly, fruit crushing is critical for first instar detection, but not for second and third instar detection. Solution type did not have a significant effect on total larval yield at any instar stage, but did affect activity levels, suggesting that motionless larvae killed by salt water are better for salt filter testing whereas active larvae in distilled water may be better for unfiltered assessment. This optimized technique offers growers accurate information regarding SWD infestation levels in their farms, allowing them to increase the sustainability, effectiveness, efficiency, and affordability of their pest management programs. Future studies should investigate whether larval movement aids in unfiltered assessment. Additionally, researchers should utilize low-level infestation to test for a difference between squished and firm berries for detecting large larvae, as fruit decomposition from heavy infestation in this study may have masked a difference.